Nikhil Arora
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Nikhil Arora
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Iurii Babyk
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Dilyar Barat
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Claude Carignan
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Priscilla Chauke
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Keir Darling
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Simón Díaz-García
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Andrej Dvornik
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Jayanne English
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Hua Gao
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Kimberly Herrmann
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Berta Margalef Bentabol
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Kevin McKinnon
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Bogdan Adrian Pastrav
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Jose Manuel Perez Martinez
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Christoph Saulder
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Amidou Sorgho
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Robert Verbeke
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Bodo Ziegler
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Quenching of Star Formation in Massive Galaxies
The effects of star formation quenching on galaxy structure and dynamical properties are an integral part of galaxy evolution studies. For instance, feedback heating from a supermassive black hole can offset the cooling of central gas and quench star formation in massive galaxies. We combine information from a version of the Munich semi-analytic model of galaxy formation and the SDSS DR8 over a representative range of stellar mass - local density. In this parameter space, the models show that the passive fraction of galaxies correlates strongly with the AGN-suppressed cooling rate and hence the mass of the BH or, equivalently, the halo mass. In that same parameter space, the quenched fraction of observed galaxies correlates strongly with the mass of the bulge, though the scatter of that relation is large. For the models to match observations, the observed large scatter in the bulge mass-BH mass relation must be fully constrained, leading to a better understanding of quenching in massive galaxies.
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The effects of star formation quenching on galaxy structure and dynamical properties are an integral part of galaxy evolution studies. For instance, feedback heating from a supermassive black hole can offset the cooling of central gas and quench star formation in massive galaxies. We combine information from a version of the Munich semi-analytic model of galaxy formation and the SDSS DR8 over a representative range of stellar mass - local density. In this parameter space, the models show that the passive fraction of galaxies correlates strongly with the AGN-suppressed cooling rate and hence the mass of the BH or, equivalently, the halo mass. In that same parameter space, the quenched fraction of observed galaxies correlates strongly with the mass of the bulge, though the scatter of that relation is large. For the models to match observations, the observed large scatter in the bulge mass-BH mass relation must be fully constrained, leading to a better understanding of quenching in massive galaxies.
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The SAMI Galaxy Survey: Gravitational Potential and Surface Density Drive Stellar Populations in Early-type Galaxies
The well-established correlations between the mass of a galaxy and the properties of its stars are considered evidence for mass driving the evolution of the stellar population. However, for our sample of 625 early-type galaxies (ETGs) with integral-field spectroscopy from the SAMI Galaxy Survey, compared to correlations with mass, the color—gravitational potential ($\Phi$), [Z/H]--$\Phi$, and age—surface density ($\Sigma$) relations show both smaller scatter and less residual trend with galaxy size. These results lead us to the following inferences: (1) the color--$\Phi$ diagram is a more precise tool for determining the developmental stage of the stellar population than the conventional color--$M$ diagram; and (2) gravitational potential is the primary regulator of global stellar metallicity, via its relation to the gas escape velocity.
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The well-established correlations between the mass of a galaxy and the properties of its stars are considered evidence for mass driving the evolution of the stellar population. However, for our sample of 625 early-type galaxies (ETGs) with integral-field spectroscopy from the SAMI Galaxy Survey, compared to correlations with mass, the color—gravitational potential ($\Phi$), [Z/H]--$\Phi$, and age—surface density ($\Sigma$) relations show both smaller scatter and less residual trend with galaxy size. These results lead us to the following inferences: (1) the color--$\Phi$ diagram is a more precise tool for determining the developmental stage of the stellar population than the conventional color--$M$ diagram; and (2) gravitational potential is the primary regulator of global stellar metallicity, via its relation to the gas escape velocity.
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Extending Scaling Relations to High Redshift with Intensity Mapping
Galaxy scaling relations have proved to be quite valuable tools in understanding galaxy structure and evolution in the relatively nearby universe. However, at very high redshifts, it is difficult and expensive to measure scalings for any but the very brightest galaxies. Line intensity mapping surveys in the next several years will provide a means of directly observing the population of faint galaxies which are undetected in traditional surveys. I will discuss how galaxy scaling relations have been critical in the development of the intensity mapping field as one of the only ways to make forecasts when designing instruments. As many of these experiments are beginning to take data, I will then discuss how intensity maps can be used both alone and in cross-correlation to probe scaling relations in galaxies extending all the way back to the Epoch of Reionization.
Galaxy scaling relations have proved to be quite valuable tools in understanding galaxy structure and evolution in the relatively nearby universe. However, at very high redshifts, it is difficult and expensive to measure scalings for any but the very brightest galaxies. Line intensity mapping surveys in the next several years will provide a means of directly observing the population of faint galaxies which are undetected in traditional surveys. I will discuss how galaxy scaling relations have been critical in the development of the intensity mapping field as one of the only ways to make forecasts when designing instruments. As many of these experiments are beginning to take data, I will then discuss how intensity maps can be used both alone and in cross-correlation to probe scaling relations in galaxies extending all the way back to the Epoch of Reionization.
Looking for low column density gas with MeerKAT & FAST
The SKA precursor MeerKAT is starting his operation as we speak and will start the Large Survey Programmes at the end of 2018. FAST has started his observations in “drift scan” mode with CRAFTS (Commensal Radio Astronomy Fast Survey) and should be able to start pointed observations in 2019. In the near future (2018-19), the best combination to study low column density HI will be to combine the sensitivity of FAST with the spatial resolution of MeerKAT. The combination of the data from those two telescopes will allow, 4-5 years before SKA1-MID, to do "cosmic web" research to levels < 5 X 10**17 cm**-2, close to 10**16 cm**-2, densities that would normally only be accessible to the full SKA around 2030. It is at those densities that we expect the galaxies to connect with the surrounding cosmic web.
For a copy of the poster, please click here
The SKA precursor MeerKAT is starting his operation as we speak and will start the Large Survey Programmes at the end of 2018. FAST has started his observations in “drift scan” mode with CRAFTS (Commensal Radio Astronomy Fast Survey) and should be able to start pointed observations in 2019. In the near future (2018-19), the best combination to study low column density HI will be to combine the sensitivity of FAST with the spatial resolution of MeerKAT. The combination of the data from those two telescopes will allow, 4-5 years before SKA1-MID, to do "cosmic web" research to levels < 5 X 10**17 cm**-2, close to 10**16 cm**-2, densities that would normally only be accessible to the full SKA around 2030. It is at those densities that we expect the galaxies to connect with the surrounding cosmic web.
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Machine Learning, Gaia, and Galactoseismology
Recently, Antoja et al discovered striking spiral patterns in various phase space projections of Solar Neighbourhood stars. Faint spirals appear in $z-v_z$ density, which can be explained by simple phase wrapping. Clearer spirals are seen when the $z-v_z$ bins are coloured in $v_R$ or $v_\phi$. We use toy model and fully self-consistent simulations to show that the spirals develop naturally from vertical bending oscillations of the disc. Performing a series expansion of the effective potential, cubic and quartic coupling terms arise, and may be crucial for understanding the morphology of the spirals. This suggests that phase space spirals might be a powerful probe of the Galactic potential. We consider that the features in the $v_R$ and $v_{\phi}$ spirals may be a result of these coupling terms. We evolve perturbed distributions of stars for 300 Myr in a simple separable model potential, and a potential with an $R-z$ coupling term. We see that features in $ v_R $ and $ v_{\phi} $ are lost in the separable case, and preserved in the coupled case. We perform similar simulations with a self consistent N-body code to observe the effects of self gravity on the spirals, in which we see similar results to those of the coupled potential simulations.
For a copy of the poster, please click here
Recently, Antoja et al discovered striking spiral patterns in various phase space projections of Solar Neighbourhood stars. Faint spirals appear in $z-v_z$ density, which can be explained by simple phase wrapping. Clearer spirals are seen when the $z-v_z$ bins are coloured in $v_R$ or $v_\phi$. We use toy model and fully self-consistent simulations to show that the spirals develop naturally from vertical bending oscillations of the disc. Performing a series expansion of the effective potential, cubic and quartic coupling terms arise, and may be crucial for understanding the morphology of the spirals. This suggests that phase space spirals might be a powerful probe of the Galactic potential. We consider that the features in the $v_R$ and $v_{\phi}$ spirals may be a result of these coupling terms. We evolve perturbed distributions of stars for 300 Myr in a simple separable model potential, and a potential with an $R-z$ coupling term. We see that features in $ v_R $ and $ v_{\phi} $ are lost in the separable case, and preserved in the coupled case. We perform similar simulations with a self consistent N-body code to observe the effects of self gravity on the spirals, in which we see similar results to those of the coupled potential simulations.
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Constraining the galaxy--halo connection with dynamical scaling relations
We use the Tully-Fisher (TFR), Faber-Jackson (FJR) and Mass Discrepancy-Acceleration (MDAR) relations, and Fundamental Plane (FP), to test a general empirical framework for the galaxy-halo connection based on abundance matching. We apply Approximate Bayesian Computation to evaluate models by comparing the predicted and observed values of summary statistics describing the relations' important features. We find some to be naturally accounted for by abundance matching, including the slope and normalisation of the TFR, the tilt of the FP and the "acceleration scale" of the MDAR. Others impose constraints on galaxy formation: haloes expand in response to disc formation, galaxy and halo specific angular momenta are similar and spirals occupy less massive haloes than ellipticals at fixed stellar mass. A few features, however, are challenging to account for with this framework; these include the correlation of velocity and size residuals in spirals and the intrinsic scatter of the MDAR and FP.
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We use the Tully-Fisher (TFR), Faber-Jackson (FJR) and Mass Discrepancy-Acceleration (MDAR) relations, and Fundamental Plane (FP), to test a general empirical framework for the galaxy-halo connection based on abundance matching. We apply Approximate Bayesian Computation to evaluate models by comparing the predicted and observed values of summary statistics describing the relations' important features. We find some to be naturally accounted for by abundance matching, including the slope and normalisation of the TFR, the tilt of the FP and the "acceleration scale" of the MDAR. Others impose constraints on galaxy formation: haloes expand in response to disc formation, galaxy and halo specific angular momenta are similar and spirals occupy less massive haloes than ellipticals at fixed stellar mass. A few features, however, are challenging to account for with this framework; these include the correlation of velocity and size residuals in spirals and the intrinsic scatter of the MDAR and FP.
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Major mergers not a viable mechanism to decrease halo concentration?
Cosmological simulations predict concentration evolves as 1/(1+z); considering background density evolution, this implies the central density of a halo must decrease as it grows. An obvious mechanism for this is through major mergers, though previous studies have shown conflicting results. We have performed over a hundred isolated binary mergers to investigate this; overall, we find that halo profiles evolve in a predictable way that is determined by the energies of the system. In general, mass is pushed into the centre of halo, as well has being ejected to large radii, resulting in halos having a higher central density, and a slightly larger concentration. Surprisingly, these results suggest that concentration is not decreased in major mergers, except in very specific cases. This could be because in cosmological conditions, equal-mass mergers as well as isolated merger events are rare. Nonetheless, this should be investigated further to fully understand the origin of the mean mass-concentration-redshift relation.
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Cosmological simulations predict concentration evolves as 1/(1+z); considering background density evolution, this implies the central density of a halo must decrease as it grows. An obvious mechanism for this is through major mergers, though previous studies have shown conflicting results. We have performed over a hundred isolated binary mergers to investigate this; overall, we find that halo profiles evolve in a predictable way that is determined by the energies of the system. In general, mass is pushed into the centre of halo, as well has being ejected to large radii, resulting in halos having a higher central density, and a slightly larger concentration. Surprisingly, these results suggest that concentration is not decreased in major mergers, except in very specific cases. This could be because in cosmological conditions, equal-mass mergers as well as isolated merger events are rare. Nonetheless, this should be investigated further to fully understand the origin of the mean mass-concentration-redshift relation.
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Visualizing Rotation Curves
A fundamental component for assessing Dark Matter content of a disk galaxy is the rotation curve tracing its dynamical mass. We present diverse explorations of galaxy kinematics using both rotation curve modelling and scientific visualization. Our rotation curve models are derived from full 3D HI and CO datasets using GalAPAGOS (Galaxy Astrophysical Parameter Acquisition by Genetic Optimization Software) which also models the gas spatial distribution. GalAPAGOS uses a genetic algorithm (Ferret: J. Fiege; www.nqube.ca) for optimization of fits and produces a family of solutions per galaxy consistent with the uncertainties in the data cube. Also the position-velocity behaviour of the observational data can be explored in 3-D, not by projecting onto 2D monitors, but by using 3D virtual reality. We have produced a preliminary visualization tool for the VIVE headset using the Unity gaming engine. Currently we explore the effect of colour in this 3D environment.
A fundamental component for assessing Dark Matter content of a disk galaxy is the rotation curve tracing its dynamical mass. We present diverse explorations of galaxy kinematics using both rotation curve modelling and scientific visualization. Our rotation curve models are derived from full 3D HI and CO datasets using GalAPAGOS (Galaxy Astrophysical Parameter Acquisition by Genetic Optimization Software) which also models the gas spatial distribution. GalAPAGOS uses a genetic algorithm (Ferret: J. Fiege; www.nqube.ca) for optimization of fits and produces a family of solutions per galaxy consistent with the uncertainties in the data cube. Also the position-velocity behaviour of the observational data can be explored in 3-D, not by projecting onto 2D monitors, but by using 3D virtual reality. We have produced a preliminary visualization tool for the VIVE headset using the Unity gaming engine. Currently we explore the effect of colour in this 3D environment.
Core formation in dark matter haloes and Ultra Diffuse Galaxies
While cold dark matter numerical simulations predict 'cuspy' density profiles for dark matter halos, observations favor shallower 'cores'. The introduction of baryonic physics alleviates this discrepancy as feedback-driven episodes of impulsive gas outflow and inflow affect the dark matter distribution. Such episodes also affect the stellar distribution and can explain the formation of Ultra Diffuse Galaxies (UDGs), which are ubiquitous in dense environments and also detected in the field, characterized by stellar masses typical of dwarf galaxies while being as extended as the Milky Way. We present a simple theoretical model for the response of dark matter haloes and UDGs to episodes of gas inflows and outflows, which provides a theoretical framework to understand the transition from dark matter cusps to cores and the formation of UDGs in the field. We further analyze UDGs in cosmological zoom-in simulations both in the field and in galaxies groups. For galaxies in the field, we find that the host haloes of UDGs have typical spin but lower concentration than non-UDGs, and that UDGs are generally more dark-matter dominated inside their effective radius. For UDGs in galaxy groups, we find that the only significant radial gradient is in specific star formation rate, UDGs being more quiescent towards the center. On appropriate orbits, satellite dwarfs can became UDGs after pericenter passage, where they lose most of the cold gas, quench, and get puffed up by tidal shocks. The weak radial trend of stellar mass and size are the outcome of the combined effect of tidal stripping, puffing up, and disruption of low-mass, diffuse systems.
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While cold dark matter numerical simulations predict 'cuspy' density profiles for dark matter halos, observations favor shallower 'cores'. The introduction of baryonic physics alleviates this discrepancy as feedback-driven episodes of impulsive gas outflow and inflow affect the dark matter distribution. Such episodes also affect the stellar distribution and can explain the formation of Ultra Diffuse Galaxies (UDGs), which are ubiquitous in dense environments and also detected in the field, characterized by stellar masses typical of dwarf galaxies while being as extended as the Milky Way. We present a simple theoretical model for the response of dark matter haloes and UDGs to episodes of gas inflows and outflows, which provides a theoretical framework to understand the transition from dark matter cusps to cores and the formation of UDGs in the field. We further analyze UDGs in cosmological zoom-in simulations both in the field and in galaxies groups. For galaxies in the field, we find that the host haloes of UDGs have typical spin but lower concentration than non-UDGs, and that UDGs are generally more dark-matter dominated inside their effective radius. For UDGs in galaxy groups, we find that the only significant radial gradient is in specific star formation rate, UDGs being more quiescent towards the center. On appropriate orbits, satellite dwarfs can became UDGs after pericenter passage, where they lose most of the cold gas, quench, and get puffed up by tidal shocks. The weak radial trend of stellar mass and size are the outcome of the combined effect of tidal stripping, puffing up, and disruption of low-mass, diffuse systems.
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The Ubiquity of Stellar Halos in Virgo Cluster Galaxies
Stellar halos encode important clues about galactic (sub-)structure and the connection between the host galaxy and its ambient intergalactic medium. We have used the deep Next Generation Virgo Survey (NGVS) for the study of these faint stellar halos. The NGVS was designed to sample the light of Virgo cluster galaxies down to faint brightness levels, below 28.8 mag arcsec$^{-2}$ in the g band. We have extracted 1D surface brightness profiles for 415 Virgo cluster galaxies from the deepest available NGVS g and i band images and compared to their SDSS counterparts from the Spectroscopic and H-band Imaging of Virgo (SHIVir) catalogue to validate our methods. Model-independent parameters were derived from our profiles and compared to their model-dependent counterparts from the NGVS team. We classify galaxies based on their 1D and 2D disk surface brightness profiles and find that about 1/3 of our well-behaved systems (those free of nearby contaminating neighbours: 293/415 galaxies) show a brightness upturn indicative of a putative stellar halo. Light profiles of halo-bearing candidate galaxies are then decomposed into bulge, disk, and halo components using various halo models (Sersic, power law, exponential) to find the fraction of light emitted from the halo. The comparison of the observed halo light fraction with previous observations and models sets constraints on galaxy formation models.
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Stellar halos encode important clues about galactic (sub-)structure and the connection between the host galaxy and its ambient intergalactic medium. We have used the deep Next Generation Virgo Survey (NGVS) for the study of these faint stellar halos. The NGVS was designed to sample the light of Virgo cluster galaxies down to faint brightness levels, below 28.8 mag arcsec$^{-2}$ in the g band. We have extracted 1D surface brightness profiles for 415 Virgo cluster galaxies from the deepest available NGVS g and i band images and compared to their SDSS counterparts from the Spectroscopic and H-band Imaging of Virgo (SHIVir) catalogue to validate our methods. Model-independent parameters were derived from our profiles and compared to their model-dependent counterparts from the NGVS team. We classify galaxies based on their 1D and 2D disk surface brightness profiles and find that about 1/3 of our well-behaved systems (those free of nearby contaminating neighbours: 293/415 galaxies) show a brightness upturn indicative of a putative stellar halo. Light profiles of halo-bearing candidate galaxies are then decomposed into bulge, disk, and halo components using various halo models (Sersic, power law, exponential) to find the fraction of light emitted from the halo. The comparison of the observed halo light fraction with previous observations and models sets constraints on galaxy formation models.
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HI observations of Local Group dwarf irregulars with the SKA pathfinders.
We present high sensitivity, intermediate resolution Hi observations of Local Group dwarf irregular galaxies using the SKA pathfinders. The KAT-7 compact baselines and the MeerKAT core configuration make these instruments sensitive to large scale, low surface brightness emission, thus allowing us to probe far out into the dark halo potential and derive the large-scale kinematics of these galaxies. Dark matter components are presented using the pseudo-isothermal and Navarro-Frenk-White prescriptions. Our results suggest that dwarf irregular galaxies are better explained with core-like than cuspy dark matter components. Like most dwarf galaxies, the stellar disk does not contribute significantly to the rotation curve even in the inner regions. The critical densities for gravitational instabilities are calcu- lated using the Toomre-Q and cloud-growth based on shear criteria. We find that in regions of star formation, the cloud growth criteria based on shear explains better the star formation in dwarf irregular galaxies
We present high sensitivity, intermediate resolution Hi observations of Local Group dwarf irregular galaxies using the SKA pathfinders. The KAT-7 compact baselines and the MeerKAT core configuration make these instruments sensitive to large scale, low surface brightness emission, thus allowing us to probe far out into the dark halo potential and derive the large-scale kinematics of these galaxies. Dark matter components are presented using the pseudo-isothermal and Navarro-Frenk-White prescriptions. Our results suggest that dwarf irregular galaxies are better explained with core-like than cuspy dark matter components. Like most dwarf galaxies, the stellar disk does not contribute significantly to the rotation curve even in the inner regions. The critical densities for gravitational instabilities are calcu- lated using the Toomre-Q and cloud-growth based on shear criteria. We find that in regions of star formation, the cloud growth criteria based on shear explains better the star formation in dwarf irregular galaxies
Deep learning of data cubes; from human hearts to galaxies
A three dimensional two-channel convolutional neural network (CNN) has been used to diagnose simulated single-photon emission computed tomography (SPECT) scans of diseased and healthy hearts. The ROC AUC of all healthy vs all unhealthy classes was 0.826, and a diagnostic map if the scans has been generated using the resulting trained CNN model. These SPECT scans share a lot of similarities to astronomical IFU and spectral data cubes. Therefore, the method shown here can be generalised to classification problems in three dimensional astronomical data. For example, automatic classification of dynamical structures and blind source detection could be achieved through a simple replacement of the medical training data with labelled astronomical training data.
A three dimensional two-channel convolutional neural network (CNN) has been used to diagnose simulated single-photon emission computed tomography (SPECT) scans of diseased and healthy hearts. The ROC AUC of all healthy vs all unhealthy classes was 0.826, and a diagnostic map if the scans has been generated using the resulting trained CNN model. These SPECT scans share a lot of similarities to astronomical IFU and spectral data cubes. Therefore, the method shown here can be generalised to classification problems in three dimensional astronomical data. For example, automatic classification of dynamical structures and blind source detection could be achieved through a simple replacement of the medical training data with labelled astronomical training data.
KAT-7 and MeerKAT observations of NGC 3621 & NGC 7424
We present observations of NGC 7424 and NGC 3621, respectively observed with KAT-7 and MeerKAT, for which we derive the rotation curves and mass models to unprecedented extents. As a precursor to the SKA, the MeerKAT telescope combines both a high spatial resolution and a large field of view, necessary to map the extended neutral hydrogen in local galaxies. The mass models were constructed for the pseudo-isothermal and NFW models. Overall, we find no solid argument of discriminating between the two models, although the results provided by the pseudo-isothermal model are the most consistent with observations.
We present observations of NGC 7424 and NGC 3621, respectively observed with KAT-7 and MeerKAT, for which we derive the rotation curves and mass models to unprecedented extents. As a precursor to the SKA, the MeerKAT telescope combines both a high spatial resolution and a large field of view, necessary to map the extended neutral hydrogen in local galaxies. The mass models were constructed for the pseudo-isothermal and NFW models. Overall, we find no solid argument of discriminating between the two models, although the results provided by the pseudo-isothermal model are the most consistent with observations.
Measuring the Scatter of the Radial Acceleration Relation
Of recent interest to galaxy formation studies are local scaling laws. One such local scaling law is the Radial Acceleration Relation (RAR) proposed by Lelli et al. (2017). Claiming that it is “One Law To Rule Them All”, Lelli et al. propose that the measured radial acceleration due to gravity follows that due to the baryonic mass tightly at all galaxy radii. So tightly, in fact, that the relation between them is consistent with zero intrinsic scatter. This RAR study was done with a galaxy sample of 175 selected spiral galaxies. I will present a RAR investigation which takes advantage of roughly 1000 spiral galaxies. While Lelli et al. have established the existence of the RAR, I am testing the zero intrinsic scatter claim. In this poster, I demonstrate the techniques used to extract the RAR for each galaxy and how the scatter is measured.
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Of recent interest to galaxy formation studies are local scaling laws. One such local scaling law is the Radial Acceleration Relation (RAR) proposed by Lelli et al. (2017). Claiming that it is “One Law To Rule Them All”, Lelli et al. propose that the measured radial acceleration due to gravity follows that due to the baryonic mass tightly at all galaxy radii. So tightly, in fact, that the relation between them is consistent with zero intrinsic scatter. This RAR study was done with a galaxy sample of 175 selected spiral galaxies. I will present a RAR investigation which takes advantage of roughly 1000 spiral galaxies. While Lelli et al. have established the existence of the RAR, I am testing the zero intrinsic scatter claim. In this poster, I demonstrate the techniques used to extract the RAR for each galaxy and how the scatter is measured.
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Probing the Hierarchical Assembly of the Virgo Cluster
The SHIVir survey has recently determined dark matter mass within the outer radius of close to 200 galaxies in the Virgo cluster. We consider theoretical predictions for the dark matter density on these scales in galaxy halos, and show that, through a combination of empirical scaling relations, it is expected to depend only weakly on stellar or halo mass, but strongly on the formation redshift of the halo. In cosmological simulations, we find this inner density is generally conserved as galaxy halos merge into clusters, and thus provides a potential tracer of the age. Plotting the dark matter density as a function of position on the sky for the entire SHIVir sample, we find that densest galaxy halos are strongly clustered around the 2-3 most massive galaxies in the cluster. Thus, it seems we may be tracing the assembly of the Virgo cluster through the properties of its galaxy halos.
The SHIVir survey has recently determined dark matter mass within the outer radius of close to 200 galaxies in the Virgo cluster. We consider theoretical predictions for the dark matter density on these scales in galaxy halos, and show that, through a combination of empirical scaling relations, it is expected to depend only weakly on stellar or halo mass, but strongly on the formation redshift of the halo. In cosmological simulations, we find this inner density is generally conserved as galaxy halos merge into clusters, and thus provides a potential tracer of the age. Plotting the dark matter density as a function of position on the sky for the entire SHIVir sample, we find that densest galaxy halos are strongly clustered around the 2-3 most massive galaxies in the cluster. Thus, it seems we may be tracing the assembly of the Virgo cluster through the properties of its galaxy halos.
Unveiling Galaxy Bias via the Halo Model, KiDS and GAMA
We have measured the projected galaxy clustering and galaxy-galaxy lensing signals using the GAMA and KiDS with the aim to study galaxy bias. Modelling our results via the halo occupation statistics allowed us to investigate the origin of the scale dependence of galaxy bias, connecting it to non-linearity and stochasticity in the models. Our study revealed that central galaxies drive non-linearities, while satellites are responsible for stochasticity. Our results are further confirmed by our analysis of the EAGLE simulations, where we find similar trends. From the observations, we also find that more massive galaxies reveal a stronger scale dependence in their bias, and out to a larger radius.
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We have measured the projected galaxy clustering and galaxy-galaxy lensing signals using the GAMA and KiDS with the aim to study galaxy bias. Modelling our results via the halo occupation statistics allowed us to investigate the origin of the scale dependence of galaxy bias, connecting it to non-linearity and stochasticity in the models. Our study revealed that central galaxies drive non-linearities, while satellites are responsible for stochasticity. Our results are further confirmed by our analysis of the EAGLE simulations, where we find similar trends. From the observations, we also find that more massive galaxies reveal a stronger scale dependence in their bias, and out to a larger radius.
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Is the scatter in the star formation main sequence globally or locally driven?
With current observations constantly improving in resolution and probing increasingly smaller sub-galactic scales, it has been found that fundamental relationship between star formation rates and accumulated stellar mass persists across all scales. However, at what point do these measurements, and ultimately the Kennicutt-Schmidt law breakdown? Furthermore, do the physics of this relation emerge from such small local scales, or are they driven by large scale, global phenomena. Here we discover three distinct behaviours by individual galaxies in the spatially-resolved star formation main sequence and a critical scale at log(M*)~8.5 which divides behaviours that are locally vs. globally dominated. We suggest that these behaviours are likely constrained by their unique mass accretion histories, age, and galactic structure.
With current observations constantly improving in resolution and probing increasingly smaller sub-galactic scales, it has been found that fundamental relationship between star formation rates and accumulated stellar mass persists across all scales. However, at what point do these measurements, and ultimately the Kennicutt-Schmidt law breakdown? Furthermore, do the physics of this relation emerge from such small local scales, or are they driven by large scale, global phenomena. Here we discover three distinct behaviours by individual galaxies in the spatially-resolved star formation main sequence and a critical scale at log(M*)~8.5 which divides behaviours that are locally vs. globally dominated. We suggest that these behaviours are likely constrained by their unique mass accretion histories, age, and galactic structure.
Environment- versus Mass-driven Quenching: Tracing Galaxy Evolution on Different Scales in the NUVrK diagram
The fact that galaxies can be classified according to their star-formation activity between "star-forming" and "quiescent" populations is now well established and this bimodality, clearly observed to redshift z~4, is the statistical expression of a (rapid) phenomenon called “quenching”. The process that is involved in the quenching of low-mass galaxies may, however, be quite different from what is involved in the quenching of massive galaxies after billion years of star formation on the Main sequence. I will discuss the existence of two quenching channels that can be identified in the NUVrK rest-frame colour diagram: one slow quenching channel followed by fairly massive galaxies, typically when reaching stellar masses of logM* ~10.64 M?, consistent with mass quenching within dark-matter halos of logMh ~12 M?, and a fast quenching channel required to explain the presence of low-mass quiescent galaxies, which we recently found to be consistent with environmental quenching of satellite galaxies.
The fact that galaxies can be classified according to their star-formation activity between "star-forming" and "quiescent" populations is now well established and this bimodality, clearly observed to redshift z~4, is the statistical expression of a (rapid) phenomenon called “quenching”. The process that is involved in the quenching of low-mass galaxies may, however, be quite different from what is involved in the quenching of massive galaxies after billion years of star formation on the Main sequence. I will discuss the existence of two quenching channels that can be identified in the NUVrK rest-frame colour diagram: one slow quenching channel followed by fairly massive galaxies, typically when reaching stellar masses of logM* ~10.64 M?, consistent with mass quenching within dark-matter halos of logMh ~12 M?, and a fast quenching channel required to explain the presence of low-mass quiescent galaxies, which we recently found to be consistent with environmental quenching of satellite galaxies.
A General Dynamical Scaling Relation Explored with CALIFA: Towards Constraining MS-MH Relation with Nearby Galaxies.
We used gas and stellar kinematics for 667 spatially resolved galaxies from CALIFA survey with the aim of studying dynamical scaling relations as the Tully&Fisher, Faber&Jackson and also a combination of them through the SK parameter defined as SK^2=KVrot^2+disp^2. TF and FJ generalized relations (early+late types) present larger dispersions and deviations from the classical ones. When we use the SK parameter all galaxies, regardless of the morphology, lie in the same scaling relation with the scatter smaller or equal to the TF and FJ ones. We interpret this relation as a consequence of the relation between dynamical mass and stellar mass in central regions of galaxies, what implies that the SK parameter is a better proxy of this dynamical mass. We compared our estimations of the dynamical mass based on the SK parameter with results based on more complex dynamical models, finding a good agreement within 0.14dex between both quantities.
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We used gas and stellar kinematics for 667 spatially resolved galaxies from CALIFA survey with the aim of studying dynamical scaling relations as the Tully&Fisher, Faber&Jackson and also a combination of them through the SK parameter defined as SK^2=KVrot^2+disp^2. TF and FJ generalized relations (early+late types) present larger dispersions and deviations from the classical ones. When we use the SK parameter all galaxies, regardless of the morphology, lie in the same scaling relation with the scatter smaller or equal to the TF and FJ ones. We interpret this relation as a consequence of the relation between dynamical mass and stellar mass in central regions of galaxies, what implies that the SK parameter is a better proxy of this dynamical mass. We compared our estimations of the dynamical mass based on the SK parameter with results based on more complex dynamical models, finding a good agreement within 0.14dex between both quantities.
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X-ray scaling relations of early-type galaxies
We present the X-ray scaling relations obtained for 94 early-type galaxies, including ellipticals, BCGs, and spirals, using archival Chandra observations. The scaling relations, L_X \propto T^{4.5\pm0.2}, M \propto T^{2.4\pm0.2}, and L_X \propto M^{2.8\pm0.3}, are significantly steeper than expected from self similarity. This steepening indicates that their atmospheres are heated above the level expected from gravitational infall alone. Energetic feedback from nuclear black holes and supernova explosions are likely heating agents. We also explore the gas mass to the total mass fraction in early-type galaxies, finding a range of 0.1-1.0%. We find no correlation between the gas-to-total mass fraction with temperature or total mass. Higher stellar velocity dispersions and higher metallicities are found in hotter, brighter, and more massive atmospheres. X-ray core radii derived from beta-model fitting are used to characterize the degree of core and cuspiness of hot atmospheres.
We present the X-ray scaling relations obtained for 94 early-type galaxies, including ellipticals, BCGs, and spirals, using archival Chandra observations. The scaling relations, L_X \propto T^{4.5\pm0.2}, M \propto T^{2.4\pm0.2}, and L_X \propto M^{2.8\pm0.3}, are significantly steeper than expected from self similarity. This steepening indicates that their atmospheres are heated above the level expected from gravitational infall alone. Energetic feedback from nuclear black holes and supernova explosions are likely heating agents. We also explore the gas mass to the total mass fraction in early-type galaxies, finding a range of 0.1-1.0%. We find no correlation between the gas-to-total mass fraction with temperature or total mass. Higher stellar velocity dispersions and higher metallicities are found in hotter, brighter, and more massive atmospheres. X-ray core radii derived from beta-model fitting are used to characterize the degree of core and cuspiness of hot atmospheres.
On the Unified Galaxy Kinematic Scaling Relation
We use data from the Sydney-AAO Multi-object Integral-field spectroscopy (SAMI) survey to study the dynamical scaling relation between galaxy stellar mass $M_*$ and the general kinematic parameter $S_K = \sqrt{K V_{rot}^2 + \sigma^2}$, combining rotation velocity $V_{rot}$ and velocity dispersion $\sigma$. We show that $K = 0.3 $ for gas component and 0.7 for stellar component return the minimum scatter for the scaling relation, and these optimal values are the same for both early-type and late-type galaxies. We also show that in the baryonic version of the scaling relation, there is an increase in the slope (~ 0.5) for both gas and stellar components of the scaling relation.
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We use data from the Sydney-AAO Multi-object Integral-field spectroscopy (SAMI) survey to study the dynamical scaling relation between galaxy stellar mass $M_*$ and the general kinematic parameter $S_K = \sqrt{K V_{rot}^2 + \sigma^2}$, combining rotation velocity $V_{rot}$ and velocity dispersion $\sigma$. We show that $K = 0.3 $ for gas component and 0.7 for stellar component return the minimum scatter for the scaling relation, and these optimal values are the same for both early-type and late-type galaxies. We also show that in the baryonic version of the scaling relation, there is an increase in the slope (~ 0.5) for both gas and stellar components of the scaling relation.
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(Mock-)observed structures of simulated galaxies
The most recent generations of cosmological hydrodynamical simulations are valuable tools for understanding the formation and evolution of galaxies. However, the interpretive power for such simulations relies fundamentally in whether they can reproduce the observed properties of galaxies. But first, it is crucial that any comparison between simulated and real galaxies is fair. To make an even-handed comparison, I put galaxies from the Illustris simulation directly in the context of observational galaxy astronomy using an unprecedentedly rigorous suite of observational realism in the Sloan Digital Sky Survey (SDSS). Parametric photometry and structural analysis of simulated galaxies with observational realism are performed using the same pipeline that was used in the analysis of 1.12 million real galaxies in the SDSS — which collectively forms the comparison sample. Comparing the size-luminosity relations and morphologies of simulated and observed galaxies reveals promising similarities and intriguing contrasts between model and observations.
The most recent generations of cosmological hydrodynamical simulations are valuable tools for understanding the formation and evolution of galaxies. However, the interpretive power for such simulations relies fundamentally in whether they can reproduce the observed properties of galaxies. But first, it is crucial that any comparison between simulated and real galaxies is fair. To make an even-handed comparison, I put galaxies from the Illustris simulation directly in the context of observational galaxy astronomy using an unprecedentedly rigorous suite of observational realism in the Sloan Digital Sky Survey (SDSS). Parametric photometry and structural analysis of simulated galaxies with observational realism are performed using the same pipeline that was used in the analysis of 1.12 million real galaxies in the SDSS — which collectively forms the comparison sample. Comparing the size-luminosity relations and morphologies of simulated and observed galaxies reveals promising similarities and intriguing contrasts between model and observations.
The dark halo-to-stellar mass ratio in S4G galaxies
We use 3.6 µm photometry for 1154 disk galaxies (i<65?) in the Spitzer Survey of Stellar Structure in Galaxies (S4G) to obtain the stellar component of the circular velocity (constant M/L). By combining the disk+bulge rotation curves with HI line width measurements, we estimate the ratio of halo-to-stellar mass (Mhalo/M*) within the optical disk. We explore how the fraction of dark matter varies with galaxy properties including morphological type and total stellar mass (M*). We confirm that faint late-type systems are more dark matter dominated. We also assess the Mhalo/M*-M* relation (and its scatter) within different disk radii using available rotation curves and optical/near-IR photometry. We find that the Mhalo/M*-M* relation is in good agreement with the best-fit models at z˜0 in ?CDM cosmological simulations (e.g. Moster et al. 2010), assuming that the dark matter halo within the optical radius comprises a constant fraction (~ 4%) of its total mass.
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We use 3.6 µm photometry for 1154 disk galaxies (i<65?) in the Spitzer Survey of Stellar Structure in Galaxies (S4G) to obtain the stellar component of the circular velocity (constant M/L). By combining the disk+bulge rotation curves with HI line width measurements, we estimate the ratio of halo-to-stellar mass (Mhalo/M*) within the optical disk. We explore how the fraction of dark matter varies with galaxy properties including morphological type and total stellar mass (M*). We confirm that faint late-type systems are more dark matter dominated. We also assess the Mhalo/M*-M* relation (and its scatter) within different disk radii using available rotation curves and optical/near-IR photometry. We find that the Mhalo/M*-M* relation is in good agreement with the best-fit models at z˜0 in ?CDM cosmological simulations (e.g. Moster et al. 2010), assuming that the dark matter halo within the optical radius comprises a constant fraction (~ 4%) of its total mass.
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Is the Local Group velocity dispersion too cold?
Satellite galaxies are commonly used as tracers to measure the line-of-sight (LOS) velocity dispersion of the dark matter halo associated with their central galaxy, and thereby to estimate the halo's mass. Observations of the local Local Group, the Milky Way and M31, give dispersions of 50 km/s, surprisingly low when compared to the 100s km/s ?CDM expectation for these systems. We show that the satellite selection gives a biased result and also present an optimal observational window that minimises the scatter LOS dispersion - halo mass relation using numerical simulations. The resulting LOS dispersions are ~1/2 the true dispersion with minimal 20% scatter. We argue that this window should be used to estimate halo masses. We conclude that the Local Group is not too cold, and has a mass of log M/Msun=12.0^{+0.8}_{-2.0}.
Satellite galaxies are commonly used as tracers to measure the line-of-sight (LOS) velocity dispersion of the dark matter halo associated with their central galaxy, and thereby to estimate the halo's mass. Observations of the local Local Group, the Milky Way and M31, give dispersions of 50 km/s, surprisingly low when compared to the 100s km/s ?CDM expectation for these systems. We show that the satellite selection gives a biased result and also present an optimal observational window that minimises the scatter LOS dispersion - halo mass relation using numerical simulations. The resulting LOS dispersions are ~1/2 the true dispersion with minimal 20% scatter. We argue that this window should be used to estimate halo masses. We conclude that the Local Group is not too cold, and has a mass of log M/Msun=12.0^{+0.8}_{-2.0}.
On the tidal stripping of Local Group dwarfs and the origin of their stellar mass-velocity dispersion relation
I use APOSTLE cosmological hydrodynamical simulations of Local Groups combined with tidal stripping models to discuss the origin and shape of the stellar mass-velocity dispersion relation observed for Local Group dwarf galaxies. I show that the tidal stripping of dwarfs embedded in cuspy dark matter halos, combined with the steep stellar mass-halo mass relation in Lambda-CDM can naturally explain the observed Mstar-Sigma relation. On the other hand, tidal stripping of dwarfs embedded in cored dark matter halos would face challenges to explain the shape of the Mstar-sigma relation. Based on our prediction, the existence of low surface brightness, low mass satellites of the Milky Way or Andromeda (e.g. Crater 2) can only be reconciled with LCDM models if they are the remnants of once massive objects heavily affected by tidal stripping. I infer their progenitor masses, radii, and velocity dispersions, and find them in remarkable agreement with scaling relations of isolated dwarfs.
I use APOSTLE cosmological hydrodynamical simulations of Local Groups combined with tidal stripping models to discuss the origin and shape of the stellar mass-velocity dispersion relation observed for Local Group dwarf galaxies. I show that the tidal stripping of dwarfs embedded in cuspy dark matter halos, combined with the steep stellar mass-halo mass relation in Lambda-CDM can naturally explain the observed Mstar-Sigma relation. On the other hand, tidal stripping of dwarfs embedded in cored dark matter halos would face challenges to explain the shape of the Mstar-sigma relation. Based on our prediction, the existence of low surface brightness, low mass satellites of the Milky Way or Andromeda (e.g. Crater 2) can only be reconciled with LCDM models if they are the remnants of once massive objects heavily affected by tidal stripping. I infer their progenitor masses, radii, and velocity dispersions, and find them in remarkable agreement with scaling relations of isolated dwarfs.
The Fundamental Plane of Bulges
We present detailed multi-component decompositions of high-quality R-band images of nearby disk galaxies selected from the Carnegie-Irvine Galaxy Survey. Much effort is invested to investigate uncertainties of bulge structural parameters introduced by various model assumptions and sky subtraction. Using robust structural parameters of the bulges, we measure their Kormendy relation and fundamental plane. We find that bulges of S0 galaxies form a surprisingly uniform population in both scaling relations, despite their wide range of prominence. And all bulges of spiral galaxies that have central stellar velocity measurements from HyperLeda follow the fundamental plane defined by S0 bulges in a tight manner. On the other hand, some small bulges (bulge-to-total ratios smaller than ~0.1) of spiral galaxies appear as 3-sigma outliers in the Kormendy relation. The outliers have low Sérsic indices (n \la 2), faint surface brightness (\mu_e > 19 mag arcsec^-2), and small sizes (\r_e \la 1 kpc), which is consistent with the previous perception of pseudobulges. As the small bulges in late-type spirals are intrinsically different from those of S0s, and environmental effects that may account for such evolution appear to be minimal, we suggest that these late-type spirals are not plausible progenitors of S0s.
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We present detailed multi-component decompositions of high-quality R-band images of nearby disk galaxies selected from the Carnegie-Irvine Galaxy Survey. Much effort is invested to investigate uncertainties of bulge structural parameters introduced by various model assumptions and sky subtraction. Using robust structural parameters of the bulges, we measure their Kormendy relation and fundamental plane. We find that bulges of S0 galaxies form a surprisingly uniform population in both scaling relations, despite their wide range of prominence. And all bulges of spiral galaxies that have central stellar velocity measurements from HyperLeda follow the fundamental plane defined by S0 bulges in a tight manner. On the other hand, some small bulges (bulge-to-total ratios smaller than ~0.1) of spiral galaxies appear as 3-sigma outliers in the Kormendy relation. The outliers have low Sérsic indices (n \la 2), faint surface brightness (\mu_e > 19 mag arcsec^-2), and small sizes (\r_e \la 1 kpc), which is consistent with the previous perception of pseudobulges. As the small bulges in late-type spirals are intrinsically different from those of S0s, and environmental effects that may account for such evolution appear to be minimal, we suggest that these late-type spirals are not plausible progenitors of S0s.
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Stellar Surface Brightness Profiles: Dwarfs to Spirals
Radial stellar surface brightness profiles of spirals are classified into three types: (I) single exponential, or the light falls off with one exponential to a break radius and then falls off (II) more steeply, or (III) less steeply. Why there are three types is still a mystery, including why light falls off as an exponential at all. Profile breaks are also found in simpler dwarf irregulars. I will highlight results from a semi-automatic fitting of a multi-wavelength data set of 141 dwarfs (Hunter & Elmegreen, 2004, 2006) including: (1) statistics of break locations and other properties as a function of wavelength and profile type that reveal strong trends from tiny dwarfs through spirals, (2) color trends and radial mass distribution as a function of profile type, and (3) the relationship of the break radius to the kinematics and density profiles of atomic hydrogen gas in the 40 LITTLE THINGS dwarfs.
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Radial stellar surface brightness profiles of spirals are classified into three types: (I) single exponential, or the light falls off with one exponential to a break radius and then falls off (II) more steeply, or (III) less steeply. Why there are three types is still a mystery, including why light falls off as an exponential at all. Profile breaks are also found in simpler dwarf irregulars. I will highlight results from a semi-automatic fitting of a multi-wavelength data set of 141 dwarfs (Hunter & Elmegreen, 2004, 2006) including: (1) statistics of break locations and other properties as a function of wavelength and profile type that reveal strong trends from tiny dwarfs through spirals, (2) color trends and radial mass distribution as a function of profile type, and (3) the relationship of the break radius to the kinematics and density profiles of atomic hydrogen gas in the 40 LITTLE THINGS dwarfs.
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Distribution of baryonic and dark matter in spiral and irregular nearby galaxies
Understanding the formation and evolution of galaxies requires a fine knowledge of the nowadays luminous and dark matter distribution within local galaxies. We present the mass distribution of a sample of 121 nearby galaxies with high quality optical velocity fields and available infra-red WISE 3.4µm data. These galaxies are part of the Fabry-Perot kinematical GHASP survey of spirals and irregular nearby galaxies. Combining the kinematical data to the WISE surface brightness data probing the emission from the old stellar population, we derive mass models allowing us to compare the luminous to the dark matter halo mass distribution in the optical regions of those galaxies. Dark matter (DM) models are constructed using the isothermal core profile and the Navarro-Frenk-White cuspy profile, as well as no-DM models following the MOND prescription. We allow the mass-to-light ratio of the baryonic disk to vary or we keep it fixed, constrained by stellar evolutionary models (WISE W1 - W2 colour) and we carry out best fit and pseudo-isothermal maximum disk models. For the DM models, the main results are: (i) the rotation curves of most galaxies are better fitted with core rather than cuspy profiles; (ii) the relation between the parameters of the dark matter and of the luminous matter components mostly depends on morphological types: e.g. different relations are found for bulgeless and bulgy systems.
Understanding the formation and evolution of galaxies requires a fine knowledge of the nowadays luminous and dark matter distribution within local galaxies. We present the mass distribution of a sample of 121 nearby galaxies with high quality optical velocity fields and available infra-red WISE 3.4µm data. These galaxies are part of the Fabry-Perot kinematical GHASP survey of spirals and irregular nearby galaxies. Combining the kinematical data to the WISE surface brightness data probing the emission from the old stellar population, we derive mass models allowing us to compare the luminous to the dark matter halo mass distribution in the optical regions of those galaxies. Dark matter (DM) models are constructed using the isothermal core profile and the Navarro-Frenk-White cuspy profile, as well as no-DM models following the MOND prescription. We allow the mass-to-light ratio of the baryonic disk to vary or we keep it fixed, constrained by stellar evolutionary models (WISE W1 - W2 colour) and we carry out best fit and pseudo-isothermal maximum disk models. For the DM models, the main results are: (i) the rotation curves of most galaxies are better fitted with core rather than cuspy profiles; (ii) the relation between the parameters of the dark matter and of the luminous matter components mostly depends on morphological types: e.g. different relations are found for bulgeless and bulgy systems.
Testing dynamical models for mass measurements in scaling relations
Estimating accurate galaxy dynamical masses is crucial to understand the intrinsic shape and scatter in a wide variety of scaling relations; e.g. the Tully-Fisher relation, stellar-to-halo-mass relation. For dynamically hot kinematic tracers with low V/s, such as stars or ionized gas, dynamical models are required to estimate the circular velocity from the observed rotation velocity and dispersion. Common models such as the Asymmetric Drift Correction, Jeans, and Schwarzschild models each have assumptions and free-parameters that limit our understanding of their accuracy. Here we systematically test these three stellar dynamical models, by comparing their mass estimates to independent estimates from concurrent cold CO gas kinematics. Over a homogeneous sample of 54 galaxies from the EDGE and CALIFA surveys, we find that all three can reproduce the CO circular velocity at the effective radius to within 10% - thereby validating these models' use for accurate dynamical mass measurements in galaxy scaling relations.
Estimating accurate galaxy dynamical masses is crucial to understand the intrinsic shape and scatter in a wide variety of scaling relations; e.g. the Tully-Fisher relation, stellar-to-halo-mass relation. For dynamically hot kinematic tracers with low V/s, such as stars or ionized gas, dynamical models are required to estimate the circular velocity from the observed rotation velocity and dispersion. Common models such as the Asymmetric Drift Correction, Jeans, and Schwarzschild models each have assumptions and free-parameters that limit our understanding of their accuracy. Here we systematically test these three stellar dynamical models, by comparing their mass estimates to independent estimates from concurrent cold CO gas kinematics. Over a homogeneous sample of 54 galaxies from the EDGE and CALIFA surveys, we find that all three can reproduce the CO circular velocity at the effective radius to within 10% - thereby validating these models' use for accurate dynamical mass measurements in galaxy scaling relations.
Galaxy structure in the big data era
Galaxy structure is one of the fundamental ways by which we can infer galaxy evolution. And with the rise of large photometric surveys, the need for faster and automatic techniques from which to determine galaxy structure has become more important. Deep learning can be the answer to such task, and have already proven to be successful in several astrophysical problems with large amounts of data, such as galaxy classification. However, in order to have an efficient deep learning algorithm able to determine with high accuracy the structural properties of galaxies, it is of most importance to train such algorithm with a large sample of galaxy images for which the structural properties are known. I will show how we can obtain such sample thanks to deep learning generative networks and simulated galaxies, and how this will help us exploit the data from large photometric surveys such as HST or JWST.
Galaxy structure is one of the fundamental ways by which we can infer galaxy evolution. And with the rise of large photometric surveys, the need for faster and automatic techniques from which to determine galaxy structure has become more important. Deep learning can be the answer to such task, and have already proven to be successful in several astrophysical problems with large amounts of data, such as galaxy classification. However, in order to have an efficient deep learning algorithm able to determine with high accuracy the structural properties of galaxies, it is of most importance to train such algorithm with a large sample of galaxy images for which the structural properties are known. I will show how we can obtain such sample thanks to deep learning generative networks and simulated galaxies, and how this will help us exploit the data from large photometric surveys such as HST or JWST.
Size evolution of the most massive galaxies since z~3
Galaxy size is an observational property which has been found to vary with galaxy mass, color and redshift and a physical property that reflects the evolutionary history of galaxies and their relationship with their dark matter halos. We present results on the size evolution of the most massive galaxies, with log(Mstar)>11.3, from the new COSMOS-Drift And SHift (DASH) survey. COSMOS-DASH provides 0.6 square degrees of HST/WFC3 F160W imaging in the COSMOS field. Separating the galaxies into star-forming and quiescent galaxies using their UVJ color, we find no statistical difference between their median sizes at z>2. The star-forming galaxies have a more rapid evolution with lookback time than quiescent galaxies, which is opposite to the effect observed in intermediate mass galaxies. We also find that at z>2.0 most massive galaxies are forming stars even though their inferred velocity dispersion are above the quenching threshold.
Galaxy size is an observational property which has been found to vary with galaxy mass, color and redshift and a physical property that reflects the evolutionary history of galaxies and their relationship with their dark matter halos. We present results on the size evolution of the most massive galaxies, with log(Mstar)>11.3, from the new COSMOS-Drift And SHift (DASH) survey. COSMOS-DASH provides 0.6 square degrees of HST/WFC3 F160W imaging in the COSMOS field. Separating the galaxies into star-forming and quiescent galaxies using their UVJ color, we find no statistical difference between their median sizes at z>2. The star-forming galaxies have a more rapid evolution with lookback time than quiescent galaxies, which is opposite to the effect observed in intermediate mass galaxies. We also find that at z>2.0 most massive galaxies are forming stars even though their inferred velocity dispersion are above the quenching threshold.
Size luminosity and size-mass relation of early type galaxies in the Frontier and COSMOS fields
Recent studies in the local universe have found that the size-luminosity relationship of elliptical galaxies shows no dependence on environment with negligible intrinsic scatter in the relation, i.e it is a 'Fundamental Line'. This poses a problem for hierarchical simulations of galaxy formation which predict an environment dependent scatter related to a galaxy's merger history. Current studies of the size-mass relations at z>1 exacerbate the problem as a much larger scatter is observed, with compact passive galaxies being a factor of 5 smaller in size at the same mass than local galaxies. If the scatter at high-redshifts is truly greater than in the local Universe, what process leads to this decrease in entropy? A key issue in probing the role of environment (halo-mass) has been studying a statistically significant sample of the cluster and field population consistently at all redshifts. We present the size-luminosity and size-mass relation of bulges, S0 and elliptical galaxies in clusters in the frontier fields and compare it to those for galaxies in COSMOS and discuss possible methods for the observed size growth.
Recent studies in the local universe have found that the size-luminosity relationship of elliptical galaxies shows no dependence on environment with negligible intrinsic scatter in the relation, i.e it is a 'Fundamental Line'. This poses a problem for hierarchical simulations of galaxy formation which predict an environment dependent scatter related to a galaxy's merger history. Current studies of the size-mass relations at z>1 exacerbate the problem as a much larger scatter is observed, with compact passive galaxies being a factor of 5 smaller in size at the same mass than local galaxies. If the scatter at high-redshifts is truly greater than in the local Universe, what process leads to this decrease in entropy? A key issue in probing the role of environment (halo-mass) has been studying a statistically significant sample of the cluster and field population consistently at all redshifts. We present the size-luminosity and size-mass relation of bulges, S0 and elliptical galaxies in clusters in the frontier fields and compare it to those for galaxies in COSMOS and discuss possible methods for the observed size growth.
Kinematic decomposition of bulges and disks for an unified understanding of scaling relation
Scaling relations are useful tools for understanding the formation and evolution of galaxies. Although galaxy dynamics can be scaled, as shown by the Fundamental Plane and the Tully-Fisher relation, these scaling relations are not applicable to all types of galaxies. We aim to quantitatively understand the distribution of angular momentum and scaling relations from the decomposition of (pressure-supported) bulge and (rotationally-supported) disk components. For the SAMI integral field spectroscopy (IFS) data, we untangle bulge and disk kinematics using pPXF with the predefined weights of components from photometric bulge/disk decomposition. Based on the 2-d kinematic maps of bulges and disks, we investigate the distribution of V/s (or ?_R) for galaxies, bulges, and disks. Looking further ahead, we explore the Tully-Fisher relation and Fundamental Plane for disk and bulge components, respectively, and seek to develop a unified understanding of galaxy dynamics and scaling relations.
Scaling relations are useful tools for understanding the formation and evolution of galaxies. Although galaxy dynamics can be scaled, as shown by the Fundamental Plane and the Tully-Fisher relation, these scaling relations are not applicable to all types of galaxies. We aim to quantitatively understand the distribution of angular momentum and scaling relations from the decomposition of (pressure-supported) bulge and (rotationally-supported) disk components. For the SAMI integral field spectroscopy (IFS) data, we untangle bulge and disk kinematics using pPXF with the predefined weights of components from photometric bulge/disk decomposition. Based on the 2-d kinematic maps of bulges and disks, we investigate the distribution of V/s (or ?_R) for galaxies, bulges, and disks. Looking further ahead, we explore the Tully-Fisher relation and Fundamental Plane for disk and bulge components, respectively, and seek to develop a unified understanding of galaxy dynamics and scaling relations.
The Fundamental Plane and large-scale Surveys
Using the huge amount of data collected by large-scale surveys and a statistical trick, we present significantly improved calibrations of the fundamental plane for 280 000 early-type galaxies. We discuss the impact of evolution, environment, and morphology on the parameters of this scaling relation. Additionally, we will illustrate, how one can use the fundamental plane data to derive peculiar motions and thereby study the large-scale distribution of dark matter.
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Using the huge amount of data collected by large-scale surveys and a statistical trick, we present significantly improved calibrations of the fundamental plane for 280 000 early-type galaxies. We discuss the impact of evolution, environment, and morphology on the parameters of this scaling relation. Additionally, we will illustrate, how one can use the fundamental plane data to derive peculiar motions and thereby study the large-scale distribution of dark matter.
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Setting the Benchmark in Dynamical Scaling Relations via Dynamical Modeling of Coma Cluster Galaxies
In this talk we present a new benchmark for the dynamical scaling relations of galaxies. Using data observed by the SAURON IFU for 42 galaxies in the Coma cluster, including the two brightest cluster galaxies, and photometric and spectral data taken from SDSS we have created detailed dynamical models for the galaxies. In addition to this we have also created simple dynamical models for a larger sample of 148 galaxies in the Coma cluster using the SDSS data, and modeled the stellar populations of these galaxies with a model independent approach. The results of these analyses have placed stringent limits on the the intrinsic scatter of dynamical scaling relations due to our negligible uncertainty in the relative distance errors in our galaxies which has been the main source of uncertainty in previous similar studies, and our ability to robustly account for the effects of dark matter and IMF variations using dynamical modelling.
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In this talk we present a new benchmark for the dynamical scaling relations of galaxies. Using data observed by the SAURON IFU for 42 galaxies in the Coma cluster, including the two brightest cluster galaxies, and photometric and spectral data taken from SDSS we have created detailed dynamical models for the galaxies. In addition to this we have also created simple dynamical models for a larger sample of 148 galaxies in the Coma cluster using the SDSS data, and modeled the stellar populations of these galaxies with a model independent approach. The results of these analyses have placed stringent limits on the the intrinsic scatter of dynamical scaling relations due to our negligible uncertainty in the relative distance errors in our galaxies which has been the main source of uncertainty in previous similar studies, and our ability to robustly account for the effects of dark matter and IMF variations using dynamical modelling.
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Dissecting the mass-size relation: comparing half-mass radii across stellar mass, spectral type, and redshift
The mass-size relation and how it changes with redshift sheds light on how galaxies and their dark matter halos evolve. Galaxy sizes are typically measured from light profiles, but mass-to-light ratio gradients can cause half-mass and half-light radii to differ. Here, we present a new method for calculating the half-mass radii of distant galaxies. We calculate the half-mass radii of ~5,000 galaxies at 1<z<2.5 in the CANDELS footprint. The galaxies span a wide range of masses and star-formation rates, and allow us to investigate how galaxy sizes evolve over mass and redshift. Furthermore, we examine the physical origins of the galaxy mass-size relation by subdividing the blue and red galaxy populations into distinct subgroups based on their spectral shape.
The mass-size relation and how it changes with redshift sheds light on how galaxies and their dark matter halos evolve. Galaxy sizes are typically measured from light profiles, but mass-to-light ratio gradients can cause half-mass and half-light radii to differ. Here, we present a new method for calculating the half-mass radii of distant galaxies. We calculate the half-mass radii of ~5,000 galaxies at 1<z<2.5 in the CANDELS footprint. The galaxies span a wide range of masses and star-formation rates, and allow us to investigate how galaxy sizes evolve over mass and redshift. Furthermore, we examine the physical origins of the galaxy mass-size relation by subdividing the blue and red galaxy populations into distinct subgroups based on their spectral shape.
How to properly point your telescope to simulations
I will present the CosMoRIA simulations, a new suite of dwarf galaxy models that continue in the spirit of the MoRIA simulations (Verbeke+ 2015). I will show that to properly derive galaxy properties, it is crucial to follow the same techniques as observers do. When realistically "observing" our simulated galaxies, they follow a broad range of observed scaling relations. I will show the rotation curves of the CosMoRIA dwarfs, obtained using observational software (e.g. Gipsy or GalAPAGOS) and discuss the baryonic Tully-Fisher relation and the Radial Acceleration Relation (McGaugh+ 2016).
I will present the CosMoRIA simulations, a new suite of dwarf galaxy models that continue in the spirit of the MoRIA simulations (Verbeke+ 2015). I will show that to properly derive galaxy properties, it is crucial to follow the same techniques as observers do. When realistically "observing" our simulated galaxies, they follow a broad range of observed scaling relations. I will show the rotation curves of the CosMoRIA dwarfs, obtained using observational software (e.g. Gipsy or GalAPAGOS) and discuss the baryonic Tully-Fisher relation and the Radial Acceleration Relation (McGaugh+ 2016).
No Title
The amount and distribution of dark matter in galaxy halos as derived from mass modelling of rotation curves, depends critically on the mass assigned to the baryonic components, in particular the stellar populations that constitute the disc and bulge. Stellar masses can be accurately derived with stellar population synthesis modelling for passively evolving populations but this is more challenging for actively star forming galaxies. An alternative to the maximum-disc hypothesis and stellar population synthesis modeling are dynamical measurements of the mass surface density of galaxy discs, which suggest sub-maximal disc situations. In this presentation I will illustrate how the inferred mass of the stellar disc affects the NFW dark matter halo parameters and demonstrate that sub-maximal discs are consistent with NFW density profiles, contrary to maximal disc situations.
The amount and distribution of dark matter in galaxy halos as derived from mass modelling of rotation curves, depends critically on the mass assigned to the baryonic components, in particular the stellar populations that constitute the disc and bulge. Stellar masses can be accurately derived with stellar population synthesis modelling for passively evolving populations but this is more challenging for actively star forming galaxies. An alternative to the maximum-disc hypothesis and stellar population synthesis modeling are dynamical measurements of the mass surface density of galaxy discs, which suggest sub-maximal disc situations. In this presentation I will illustrate how the inferred mass of the stellar disc affects the NFW dark matter halo parameters and demonstrate that sub-maximal discs are consistent with NFW density profiles, contrary to maximal disc situations.
Dependence of Spiral Arm Pitch Angle on Galactic Properties
We present detail measurement of the tightness of spiral arms (pitch angle), measured using SDSS images in a sample of 77 galaxies from the CALIFA survey. We aim to systematically establish the dependence of pitch angle on galaxy morphology, mass, and kinematics to reveal the physical origin of spiral arms. Combined with galactic properties derived from previous studies, we find that the measured pitch angle decreases loosely with later Hubble type, increasing stellar mass, increasing bulge mass, and increasing bulge-to-total light ratio. Contrary to previous claims, the pitch angle of arms correlates only weakly with the shear rate of the rotational curve. Instead, the pitch angle correlates most strongly with the central stellar velocity dispersion (sigma_c): galaxies with large sigma_c have small pitch angle, while galaxies with low sigma_c have large pitch angle but with some having small pitch angle. This result can be explained by global modes theory predicting only wave mode with tight arms survive for high mass concentration.
We present detail measurement of the tightness of spiral arms (pitch angle), measured using SDSS images in a sample of 77 galaxies from the CALIFA survey. We aim to systematically establish the dependence of pitch angle on galaxy morphology, mass, and kinematics to reveal the physical origin of spiral arms. Combined with galactic properties derived from previous studies, we find that the measured pitch angle decreases loosely with later Hubble type, increasing stellar mass, increasing bulge mass, and increasing bulge-to-total light ratio. Contrary to previous claims, the pitch angle of arms correlates only weakly with the shear rate of the rotational curve. Instead, the pitch angle correlates most strongly with the central stellar velocity dispersion (sigma_c): galaxies with large sigma_c have small pitch angle, while galaxies with low sigma_c have large pitch angle but with some having small pitch angle. This result can be explained by global modes theory predicting only wave mode with tight arms survive for high mass concentration.
Dynamical Scaling Relations for all Galaxy Types
I suggest to present scaling relations based on dynamically derived total masses for nearby galaxies. Exploiting IFU data from the CALIFA survey we derived dynamical masses with the JAM method for 300 galaxies of all morphological types (s. Leung+18). Due to the homogeneous selection of the CALIFA sample all our results can be corrected for volume and cosmic variance effects. All galaxies lie on the same Virial Plane, i.e. the Fundamental Plane based on total masses. Using stellar masses instead all galaxy types follow still a narrow relation but with a tilt with respect to the virial prediction. Within the small scatter of the Virial Plane we do not find any additional dependence on global galaxy parameters like angular momentum, velocity anisotropy, star formation rate/history, or morphological parameters. In addition, I shall also show the Faber-Jackson, Tully-Fisher, Mass-Size, Mass-SFR, and Mass-Metallicity scaling relations.
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I suggest to present scaling relations based on dynamically derived total masses for nearby galaxies. Exploiting IFU data from the CALIFA survey we derived dynamical masses with the JAM method for 300 galaxies of all morphological types (s. Leung+18). Due to the homogeneous selection of the CALIFA sample all our results can be corrected for volume and cosmic variance effects. All galaxies lie on the same Virial Plane, i.e. the Fundamental Plane based on total masses. Using stellar masses instead all galaxy types follow still a narrow relation but with a tilt with respect to the virial prediction. Within the small scatter of the Virial Plane we do not find any additional dependence on global galaxy parameters like angular momentum, velocity anisotropy, star formation rate/history, or morphological parameters. In addition, I shall also show the Faber-Jackson, Tully-Fisher, Mass-Size, Mass-SFR, and Mass-Metallicity scaling relations.
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Constraints on the low mass end of the Stellar Mass to Halo Mass scaling relation
The Stellar Mass to Halo Mass (SMHM) scaling relation, derived assuming abundance matching, is well constrained for halos of masses > 10^11 solar masses. Below this mass, there is a significant uncertainty, largely due to the lack of observed low-mass galaxies. I will show that the number of predicted dwarf galaxies in the Local Volume is drastically influenced by the various existing SMHM relations in the literature. I will then present our strategy for finding these low-mass field galaxies as part of the Dragonfly Wide-Field Survey and understand the dependence of their properties on the environment. We will use these data to empirically constrain the SMHM relation at the low mass end. Studying low-mass field galaxies, beyond our Local Group is essential for understanding the nature of low-mass dark matter halos (Danieli et al. 2016; Danieli, van Dokkum and Conroy et al. 2017).
The Stellar Mass to Halo Mass (SMHM) scaling relation, derived assuming abundance matching, is well constrained for halos of masses > 10^11 solar masses. Below this mass, there is a significant uncertainty, largely due to the lack of observed low-mass galaxies. I will show that the number of predicted dwarf galaxies in the Local Volume is drastically influenced by the various existing SMHM relations in the literature. I will then present our strategy for finding these low-mass field galaxies as part of the Dragonfly Wide-Field Survey and understand the dependence of their properties on the environment. We will use these data to empirically constrain the SMHM relation at the low mass end. Studying low-mass field galaxies, beyond our Local Group is essential for understanding the nature of low-mass dark matter halos (Danieli et al. 2016; Danieli, van Dokkum and Conroy et al. 2017).
Radio Astronomy and the Search for Cold Dark Matter Axions
A number of laboratory searches are underway for cold dark matter (CDM) axions, relativistic solar axions, and ultra-light axions. The interest in axions as CDM candidates is motivated by their potential to account for all of the inferred value of OmegaDM ~ 0.26 in the standard LambdaCDM model. Indeed, the value of OmegaDM ~ 0.26 could be set by the axion mass. We investigate the possibility of complementing existing axion search experiments with radio telescope observations in an attempt to detect axion conversion in astrophysical magnetic fields. Searching for a CDM axion signal from a large-scale astrophysical environment provides new challenges, with the magnetic field structure playing a crucial role in both the rate of interaction and the properties of the observed photon. With a predicted frequency in the radio band (200 MHz–200 GHz) and a distinguishable spectral profile, next-generation radio telescopes may offer new opportunities for detection.
A number of laboratory searches are underway for cold dark matter (CDM) axions, relativistic solar axions, and ultra-light axions. The interest in axions as CDM candidates is motivated by their potential to account for all of the inferred value of OmegaDM ~ 0.26 in the standard LambdaCDM model. Indeed, the value of OmegaDM ~ 0.26 could be set by the axion mass. We investigate the possibility of complementing existing axion search experiments with radio telescope observations in an attempt to detect axion conversion in astrophysical magnetic fields. Searching for a CDM axion signal from a large-scale astrophysical environment provides new challenges, with the magnetic field structure playing a crucial role in both the rate of interaction and the properties of the observed photon. With a predicted frequency in the radio band (200 MHz–200 GHz) and a distinguishable spectral profile, next-generation radio telescopes may offer new opportunities for detection.
Impact of Dust and Inclinations on Galaxy Sizes
I exploit N-body simulations (Illustris, NIHAO) to study the impact of size measurements and dust geometries on fundamental galaxy structural parameters and dynamical mass profiles. Size measurements are however ill-defined, as they may result from highly subjective model assumptions (e.g. B/D decompositions), or depend strongly, for model-independent sizes such as isophotal and effective radii, on the assumed three-dimensional structure of a system. With the help of radiative transfer codes, we create optical images of galaxies with and without dust and study the variation in size as a function of inclinations. We also study the impact of these variations on the scatter of the size-mass relation and compare with observations. In the dust-free case, sizes derived for edge-on and face-on orientations differ on average by 7% (17%) for the half-light (isophotal) radii in massive galaxies. The next step involves studying, with high-resolution zoom-in simulations, the sizes of galaxies having dust distributed in a clumpy medium. Project galaxies sizes are expected to change significantly.
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I exploit N-body simulations (Illustris, NIHAO) to study the impact of size measurements and dust geometries on fundamental galaxy structural parameters and dynamical mass profiles. Size measurements are however ill-defined, as they may result from highly subjective model assumptions (e.g. B/D decompositions), or depend strongly, for model-independent sizes such as isophotal and effective radii, on the assumed three-dimensional structure of a system. With the help of radiative transfer codes, we create optical images of galaxies with and without dust and study the variation in size as a function of inclinations. We also study the impact of these variations on the scatter of the size-mass relation and compare with observations. In the dust-free case, sizes derived for edge-on and face-on orientations differ on average by 7% (17%) for the half-light (isophotal) radii in massive galaxies. The next step involves studying, with high-resolution zoom-in simulations, the sizes of galaxies having dust distributed in a clumpy medium. Project galaxies sizes are expected to change significantly.
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Stellar Population Properties and Dynamical Modelling of Early-Type Galaxies with MUSE
The initial mass function has recently been discovered to vary systematically between, and also within, galaxies. However at this point, it is not obvious what galaxy property (or properties) the IMF normalisation scales with. We utilise high quality, spatially-resolved MUSE spectroscopy of three nearby early-type galaxies, allowing us to compare the IMF normalisation derived from both stellar population and dynamical modelling approaches, for galaxies spanning a range of velocity dispersion. I will present the results of our stellar population and dynamical modelling analyses, with a particular focus on how the IMF varies as a function of both global and local properties, and what constraints we can place on dark matter within these galaxies.
The initial mass function has recently been discovered to vary systematically between, and also within, galaxies. However at this point, it is not obvious what galaxy property (or properties) the IMF normalisation scales with. We utilise high quality, spatially-resolved MUSE spectroscopy of three nearby early-type galaxies, allowing us to compare the IMF normalisation derived from both stellar population and dynamical modelling approaches, for galaxies spanning a range of velocity dispersion. I will present the results of our stellar population and dynamical modelling analyses, with a particular focus on how the IMF varies as a function of both global and local properties, and what constraints we can place on dark matter within these galaxies.
Clues on the evolution of massive galaxies from the mass - size diagram
The dominant formation process of massive galaxies can be pinpointed by investigating how stellar kinematics and the black hole mass (Mbh) vary as a function of the host galaxy stellar mass and size. I will show the evidence for a change in Mbh above a critical galaxy mass. Next to the dependence on the velocity dispersion, Mbh in massive galaxies depends also on the galaxy stellar mass, which I will argue is an outcome of a sequence of dissipation-less mergers. Drawing on the results of the M3G survey, a campaign to observe massive galaxies with MUSE, I will present a bimodal distribution of kinematic misalignments for galaxies more massive than 10e12 Msun, with prolate-like rotation incidence of almost 50%. The change in the stellar kinematics of galaxies on the mass - size diagram reflects the change of the Mbh dependence, supporting dissipation-less major mergers as the dominant channel of massive galaxy formation.
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The dominant formation process of massive galaxies can be pinpointed by investigating how stellar kinematics and the black hole mass (Mbh) vary as a function of the host galaxy stellar mass and size. I will show the evidence for a change in Mbh above a critical galaxy mass. Next to the dependence on the velocity dispersion, Mbh in massive galaxies depends also on the galaxy stellar mass, which I will argue is an outcome of a sequence of dissipation-less mergers. Drawing on the results of the M3G survey, a campaign to observe massive galaxies with MUSE, I will present a bimodal distribution of kinematic misalignments for galaxies more massive than 10e12 Msun, with prolate-like rotation incidence of almost 50%. The change in the stellar kinematics of galaxies on the mass - size diagram reflects the change of the Mbh dependence, supporting dissipation-less major mergers as the dominant channel of massive galaxy formation.
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Connecting local and global galaxy-halo scaling relations via spatially resolved semi-empirical models
Traditional abundance matching derives empirical relationships between global galaxy properties (such as stellar mass) and halo properties (such as virial mass). This technique has recently been extended (e.g., Somerville et al. 2018) to derive constraints on galaxy structural properties (such as radial size) using halo structural properties (such as spin or concentration). In this talk, I will describe a novel further extension that we term "spatially resolved" abundance matching. Here, we make use of structural abundance matching to predict stellar mass profiles, and combine these with empirical spatially resolved scaling relations between stellar mass surface density, star formation rate surface density, cold gas mass surface density, gas metallicity, and rotation velocity. We then use the predicted distributions of structural properties for cosmological populations of halos from large-volume N-body simulations to explore what these local scaling relations imply for global galaxy scaling relations and their evolution.
Traditional abundance matching derives empirical relationships between global galaxy properties (such as stellar mass) and halo properties (such as virial mass). This technique has recently been extended (e.g., Somerville et al. 2018) to derive constraints on galaxy structural properties (such as radial size) using halo structural properties (such as spin or concentration). In this talk, I will describe a novel further extension that we term "spatially resolved" abundance matching. Here, we make use of structural abundance matching to predict stellar mass profiles, and combine these with empirical spatially resolved scaling relations between stellar mass surface density, star formation rate surface density, cold gas mass surface density, gas metallicity, and rotation velocity. We then use the predicted distributions of structural properties for cosmological populations of halos from large-volume N-body simulations to explore what these local scaling relations imply for global galaxy scaling relations and their evolution.
Studies of the local dark matter velocity distribution using new cosmological simulations
The annihilation signal of dark matter (DM) relies significantly on its local velocity distribution. An accurate model of the local DM velocity distribution is essential to obtain reliable constraints on DM particle properties, currently a simple Gaussian distribution is used. We investigate the local DM velocity distribution using Milky Way mass-like galaxies generated from new, high-resolution, hydrodynamical cosmological simulations. Accounting for the effects of baryon physics, alignment of the galactic disk and the seasonal velocity variation. We define the local region over a radial distance of 8.5±1 kpc and up to 1 kpc from the galactic plane. Results show the velocity distribution in the local neighbourhood is not a simple Gaussian. We are investigating the effects of the triaxial shape of the DM halo and of the recently disrupted substructures may have in the local neighbourhood. This work aims to improve the constraints for the direct detection of DM.
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The annihilation signal of dark matter (DM) relies significantly on its local velocity distribution. An accurate model of the local DM velocity distribution is essential to obtain reliable constraints on DM particle properties, currently a simple Gaussian distribution is used. We investigate the local DM velocity distribution using Milky Way mass-like galaxies generated from new, high-resolution, hydrodynamical cosmological simulations. Accounting for the effects of baryon physics, alignment of the galactic disk and the seasonal velocity variation. We define the local region over a radial distance of 8.5±1 kpc and up to 1 kpc from the galactic plane. Results show the velocity distribution in the local neighbourhood is not a simple Gaussian. We are investigating the effects of the triaxial shape of the DM halo and of the recently disrupted substructures may have in the local neighbourhood. This work aims to improve the constraints for the direct detection of DM.
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Supermassive black holes as the regulators of star formation in central galaxies
We present a relationship between the black hole (BH) mass, stellar mass, and star formation rate (SFR) of a diverse group of 91 local galaxies with dynamically-measured BH masses. We find that the specific SFR is a smoothly decreasing function of the BH-stellar mass ratio. We propose a physical framework where the amount of heating from low-accretion rate BH feedback suppresses a certain amount of cooling onto the galaxy and results in a corresponding SFR. Our results present a powerful diagnostic with which to test various prescriptions of BH feedback in models. Using the new IllustrisTNG simulation, we compare our observational results with simulation data to test our physical framework. In addition, we use dozens of other TNG runs with varying physics implementations to show how observable galaxy trends and correlations are affected by changes in BH feedback physics, thereby providing a pathway to physically interpret observations.
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We present a relationship between the black hole (BH) mass, stellar mass, and star formation rate (SFR) of a diverse group of 91 local galaxies with dynamically-measured BH masses. We find that the specific SFR is a smoothly decreasing function of the BH-stellar mass ratio. We propose a physical framework where the amount of heating from low-accretion rate BH feedback suppresses a certain amount of cooling onto the galaxy and results in a corresponding SFR. Our results present a powerful diagnostic with which to test various prescriptions of BH feedback in models. Using the new IllustrisTNG simulation, we compare our observational results with simulation data to test our physical framework. In addition, we use dozens of other TNG runs with varying physics implementations to show how observable galaxy trends and correlations are affected by changes in BH feedback physics, thereby providing a pathway to physically interpret observations.
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Galaxy Scaling Relations at Ultra-high Redshift: Predictions from Semi-Analytic Models
We present physical properties for bulk populations of galaxies predicted by the well-established Santa Cruz semi-analytic model with the recently implemented multiphase gas partitioning and molecular hydrogen-based star formation recipes. Our model predicted UV LFs have been shown to match extremely well with existing observations over a wide range of redshifts (z = 4 - 10), and we show examples of scaling relations, such as the m*-SFR relation, m*-M_h relation, m*-size relation, that we predict at z > 4. Taking advantage of our model’s high computational efficiency, we systematically vary relevant model elements to explore how predictions are affected by the uncertainties in poorly constrained subgrid physical processes. With the high dynamic range afforded by our SAM, we are also able to simulate large populations of high-z objects and study how these uncertainties may impact the number density of high-z galaxies, which play an extremely important role in cosmic evolution and may help to indirectly constrain the nature of dark matter.
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We present physical properties for bulk populations of galaxies predicted by the well-established Santa Cruz semi-analytic model with the recently implemented multiphase gas partitioning and molecular hydrogen-based star formation recipes. Our model predicted UV LFs have been shown to match extremely well with existing observations over a wide range of redshifts (z = 4 - 10), and we show examples of scaling relations, such as the m*-SFR relation, m*-M_h relation, m*-size relation, that we predict at z > 4. Taking advantage of our model’s high computational efficiency, we systematically vary relevant model elements to explore how predictions are affected by the uncertainties in poorly constrained subgrid physical processes. With the high dynamic range afforded by our SAM, we are also able to simulate large populations of high-z objects and study how these uncertainties may impact the number density of high-z galaxies, which play an extremely important role in cosmic evolution and may help to indirectly constrain the nature of dark matter.
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Is local mass density the driver of stellar population properties?
The advent of integral field spectroscopy allows studying not only the global scaling relations between stellar population properties and a galaxy's mass, but also the analogous local scaling relations with mass surface density. I will report on two newly discovered aspects of local scaling relations derived from the CALIFA dataset, which uniquely probes local scales of ~1 kpc for a complete sample of nearby galaxies. 1) The emergence of a bimodality in the local stellar age distribution, across all galaxy morphologies, as the result of two distinct scaling relations between age and stellar mass surface density (mu*). I will discuss the implications for the evolution and growth of mu*. 2) For early-type galaxies, the existence of tight and quasi-universal local relations between mu* and the stellar population's age and metallicity. This further highlights the key and universal role of mu* in driving the internal evolution of galaxies.
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The advent of integral field spectroscopy allows studying not only the global scaling relations between stellar population properties and a galaxy's mass, but also the analogous local scaling relations with mass surface density. I will report on two newly discovered aspects of local scaling relations derived from the CALIFA dataset, which uniquely probes local scales of ~1 kpc for a complete sample of nearby galaxies. 1) The emergence of a bimodality in the local stellar age distribution, across all galaxy morphologies, as the result of two distinct scaling relations between age and stellar mass surface density (mu*). I will discuss the implications for the evolution and growth of mu*. 2) For early-type galaxies, the existence of tight and quasi-universal local relations between mu* and the stellar population's age and metallicity. This further highlights the key and universal role of mu* in driving the internal evolution of galaxies.
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Extending Scaling Relations to High Redshift with Intensity Mapping
Galaxy scaling relations have proved to be quite valuable tools in understanding galaxy structure and evolution in the relatively nearby universe. However, at very high redshifts, it is difficult and expensive to measure scalings for any but the very brightest galaxies. Line intensity mapping surveys in the next several years will provide a means of directly observing the population of faint galaxies which are undetected in traditional surveys. I will discuss how galaxy scaling relations have been critical in the development of the intensity mapping field as one of the only ways to make forecasts when designing instruments. As many of these experiments are beginning to take data, I will then discuss how intensity maps can be used both alone and in cross-correlation to probe scaling relations in galaxies extending all the way back to the Epoch of Reionization.
Galaxy scaling relations have proved to be quite valuable tools in understanding galaxy structure and evolution in the relatively nearby universe. However, at very high redshifts, it is difficult and expensive to measure scalings for any but the very brightest galaxies. Line intensity mapping surveys in the next several years will provide a means of directly observing the population of faint galaxies which are undetected in traditional surveys. I will discuss how galaxy scaling relations have been critical in the development of the intensity mapping field as one of the only ways to make forecasts when designing instruments. As many of these experiments are beginning to take data, I will then discuss how intensity maps can be used both alone and in cross-correlation to probe scaling relations in galaxies extending all the way back to the Epoch of Reionization.
Scaling relations for Milky Way satellites - Hints from hydrodynamical simulations
The dwarf galaxies of the Local Group are among the most well studied galaxies we know and several scaling relations like e.g. the mass-metallicity, size-velocity dispersion or stellar mass-dark matter mass relation could be observationally established. Using a new set of high-resolution ($m_{\rm gas}<10^5\Msun$) hydrodynamical simulations of Milky Way like galaxies and their dwarf galaxy populations performed within the NIHAO project we investigate the physics that sets and shapes the scaling relations of Local Group dwarf galaxies. We verify that the dwarf galaxies in our simulations are in very good agreement with observed Local Group scaling relations. For satellite galaxies these relations are already present before infall and are successively shaped by environmental effects. Especially the size-velocity dispersion relation is largely influenced by tidal forces and mass removal: it creates a very flat stellar velocity dispersion profile, and it reduces the dark matter content at all scales (even in the center), which in turn lowers the stellar velocity on scales around the half-light radius even when stellar mass loss is negligible.
The dwarf galaxies of the Local Group are among the most well studied galaxies we know and several scaling relations like e.g. the mass-metallicity, size-velocity dispersion or stellar mass-dark matter mass relation could be observationally established. Using a new set of high-resolution ($m_{\rm gas}<10^5\Msun$) hydrodynamical simulations of Milky Way like galaxies and their dwarf galaxy populations performed within the NIHAO project we investigate the physics that sets and shapes the scaling relations of Local Group dwarf galaxies. We verify that the dwarf galaxies in our simulations are in very good agreement with observed Local Group scaling relations. For satellite galaxies these relations are already present before infall and are successively shaped by environmental effects. Especially the size-velocity dispersion relation is largely influenced by tidal forces and mass removal: it creates a very flat stellar velocity dispersion profile, and it reduces the dark matter content at all scales (even in the center), which in turn lowers the stellar velocity on scales around the half-light radius even when stellar mass loss is negligible.
Star Formation Histories of $Z\sim1$ Galaxies in LEGA-C
Scaling relations between global galaxy properties and star-formation rate (SFR) activity suggest a close link between galaxy mass and dynamics on the one hand, and star-formation history (SFH) on the other. Due to the need for high-S/N, high-resolution continuum spectroscopy, reconstructing SFHs was previously only possible for local galaxies. The VLT LEGA-C Survey has collected high-quality spectra of $\sim3000$ galaxies at redshifts z\,$=0.6-1$, with the aim of revealing the internal dynamics and stellar population content of these galaxies. Based on reconstructed SFHs we show that: 1) the stellar ages of $z\sim1$ galaxies correlate strongly with their stellar velocity dispersions and ongoing SF activity; 2) the SFHs of L$_*$ galaxies with ongoing SF activity, unlike their present-day counterparts, are near their peak in SFR. By combining, for the first time, the lookback approach with the archaeological approach, these results illustrate the potential offered by high-S/N spectroscopy of high-redshift galaxies.
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Scaling relations between global galaxy properties and star-formation rate (SFR) activity suggest a close link between galaxy mass and dynamics on the one hand, and star-formation history (SFH) on the other. Due to the need for high-S/N, high-resolution continuum spectroscopy, reconstructing SFHs was previously only possible for local galaxies. The VLT LEGA-C Survey has collected high-quality spectra of $\sim3000$ galaxies at redshifts z\,$=0.6-1$, with the aim of revealing the internal dynamics and stellar population content of these galaxies. Based on reconstructed SFHs we show that: 1) the stellar ages of $z\sim1$ galaxies correlate strongly with their stellar velocity dispersions and ongoing SF activity; 2) the SFHs of L$_*$ galaxies with ongoing SF activity, unlike their present-day counterparts, are near their peak in SFR. By combining, for the first time, the lookback approach with the archaeological approach, these results illustrate the potential offered by high-S/N spectroscopy of high-redshift galaxies.
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Predictably Missing Satellites: Subhalo Abundances in Milky Way-like Halos
On small scales there are discrepancies between the standard Cold Dark Matter (CDM) model and observations. The 'missing satellites problem' infamously describes the overabundance of subhalos from CDM simulations compared to the satellites observed in the Milky Way. There have been numerous proposed solutions to the discrepancy, however none account for the properties of the Milky Way. Motivated by recent studies that show that the Milky Way is more atypical than expected (eg. Licquia et al. 2015) we look at a novel perspective analyzing the Milky Way's host halo properties - concentration, spin, shape, and scale factor of the last major merger - and their correlation with subhalo abundances. We present an N-body investigation of the subhalo-host halo connection by comparing the Mao et al. 2015 zoom-in simulations of Milky Way-mass halos to Milky Way data, concluding that even in dark matter simulations of the same mass the Milky Way is at the edge of host halo property distributions. From our data we determine that host halo properties are indicative of subhalo abundances for at least low mass subhalos. From our simulations and the measured properties of the Milky Way dark matter halo we build a model of Milky Way subhalo abundance based on its halo properties, and conclude that there should be at least 25-40\% fewer subhalos than have previously been predicted for the Milky Way.
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On small scales there are discrepancies between the standard Cold Dark Matter (CDM) model and observations. The 'missing satellites problem' infamously describes the overabundance of subhalos from CDM simulations compared to the satellites observed in the Milky Way. There have been numerous proposed solutions to the discrepancy, however none account for the properties of the Milky Way. Motivated by recent studies that show that the Milky Way is more atypical than expected (eg. Licquia et al. 2015) we look at a novel perspective analyzing the Milky Way's host halo properties - concentration, spin, shape, and scale factor of the last major merger - and their correlation with subhalo abundances. We present an N-body investigation of the subhalo-host halo connection by comparing the Mao et al. 2015 zoom-in simulations of Milky Way-mass halos to Milky Way data, concluding that even in dark matter simulations of the same mass the Milky Way is at the edge of host halo property distributions. From our data we determine that host halo properties are indicative of subhalo abundances for at least low mass subhalos. From our simulations and the measured properties of the Milky Way dark matter halo we build a model of Milky Way subhalo abundance based on its halo properties, and conclude that there should be at least 25-40\% fewer subhalos than have previously been predicted for the Milky Way.
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The Dependence of the Stellar Mass - Halo Mass Relation on Environment and Cosmic Time
The Stellar Mass-Halo Mass (SMHM) relation provides insight into the galaxy-dark matter halo connection. In Golden-Marx & Miller (2018), we incorporate the magnitude gap into the cluster SMHM relation. We observe that at fixed halo mass, clusters with larger magnitude gaps have larger central galaxy stellar masses. We also see this in semi-analytic simulations, which suggests that it can be explained by the hierarchical growth of centrals. Accounting for the magnitude gap significantly reduces the error on the inferred SMHM relation’s slope. It also reduces the inferred intrinsic scatter to below 0.1 dex, thus strictly limiting the model space that can explain the stellar mass growth in centrals. Hierarchical growth also predicts that the central’s stellar mass and magnitude gap decrease with increasing lookback time. To test this prediction, we present our latest results that use SDSS RedMapper to extend our analysis from z = 0.1 to z = 0.3.
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The Stellar Mass-Halo Mass (SMHM) relation provides insight into the galaxy-dark matter halo connection. In Golden-Marx & Miller (2018), we incorporate the magnitude gap into the cluster SMHM relation. We observe that at fixed halo mass, clusters with larger magnitude gaps have larger central galaxy stellar masses. We also see this in semi-analytic simulations, which suggests that it can be explained by the hierarchical growth of centrals. Accounting for the magnitude gap significantly reduces the error on the inferred SMHM relation’s slope. It also reduces the inferred intrinsic scatter to below 0.1 dex, thus strictly limiting the model space that can explain the stellar mass growth in centrals. Hierarchical growth also predicts that the central’s stellar mass and magnitude gap decrease with increasing lookback time. To test this prediction, we present our latest results that use SDSS RedMapper to extend our analysis from z = 0.1 to z = 0.3.
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Time invariance of the stellar mass--halo mass at high halo mass end: implications on the buildup of cluster galaxy population
The scaling between the total stellar mass of galaxies and cluster mass (Mstar--Mcl) is critical in understanding the buildup of the cluster galaxy population: while its amplitude depends on the star formation efficiency averaged over all progenitor halos, its slope is important in evaluating the strength of tidal stripping in dense environments. In addition, the BCG stellar mass--cluster mass correlation constrains the AGN feedback efficiency in cluster centers. We have measured these correlations with a large cluster sample at z=0.3-1 from the Subaru Hyper Suprime-Cam survey. The Mstar--Mcl relation is found to be independent of redshift, with a slope of 0.7 that indicates a large degree of stripping for member galaxies (implying a huge amount of intracluster light). The invariance in time of the scaling is challenging to reproduce by state-of-the-art simulations such as IllustrisTNG. We discuss implications of these scaling relations on the cluster assembly history.
The scaling between the total stellar mass of galaxies and cluster mass (Mstar--Mcl) is critical in understanding the buildup of the cluster galaxy population: while its amplitude depends on the star formation efficiency averaged over all progenitor halos, its slope is important in evaluating the strength of tidal stripping in dense environments. In addition, the BCG stellar mass--cluster mass correlation constrains the AGN feedback efficiency in cluster centers. We have measured these correlations with a large cluster sample at z=0.3-1 from the Subaru Hyper Suprime-Cam survey. The Mstar--Mcl relation is found to be independent of redshift, with a slope of 0.7 that indicates a large degree of stripping for member galaxies (implying a huge amount of intracluster light). The invariance in time of the scaling is challenging to reproduce by state-of-the-art simulations such as IllustrisTNG. We discuss implications of these scaling relations on the cluster assembly history.
The dust effects on galaxy scaling relations
Accurate galaxy scaling relations are essential for a successful model of galaxy formation and evolution as they provide direct information about the physical mechanisms of galaxy assembly over cosmic time. We present here a detailed analysis of a sample of nearby spiral galaxies taken from the KINGFISH survey. The photometric parameters of the morphological components are obtained from bulge-disk decompositions using GALFIT data analysis algorithm, with surface photometry of the sample performed beforehand. The method and the library of numerical results previously obtained in Pastrav et al. (2013a,b) are used to correct the measured photometric parameters for inclination, dust and decomposition effects in order to derive their intrinsic values. Galaxy scaling relations are then presented with and without corrections for these effects, at various wavelengths and specific dust opacities. While our sample is rather small, it is sufficient to emphasize the influence of galaxy environment (dust, in this case) when deriving scaling relations.
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Accurate galaxy scaling relations are essential for a successful model of galaxy formation and evolution as they provide direct information about the physical mechanisms of galaxy assembly over cosmic time. We present here a detailed analysis of a sample of nearby spiral galaxies taken from the KINGFISH survey. The photometric parameters of the morphological components are obtained from bulge-disk decompositions using GALFIT data analysis algorithm, with surface photometry of the sample performed beforehand. The method and the library of numerical results previously obtained in Pastrav et al. (2013a,b) are used to correct the measured photometric parameters for inclination, dust and decomposition effects in order to derive their intrinsic values. Galaxy scaling relations are then presented with and without corrections for these effects, at various wavelengths and specific dust opacities. While our sample is rather small, it is sufficient to emphasize the influence of galaxy environment (dust, in this case) when deriving scaling relations.
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Scaling relations and recent star formation in cluster galaxies
We use different representations of the Tully-Fisher relation (TFR) to investigate quantitatively the evolutionary status of galaxies in two clusters at z~0.5 and 1.4, respectively, using ESO-VIMOS and FORS2 spectra. While the B-band TFR is sensitive to recent star-formation episodes, the stellar-mass TFR tracks the overall evolution of the underlying stellar population. The combination of these two schemes allows us to identify galaxies that might be suffering cluster-specific interactions as outliers in the B-band TFR, while these very same galaxies display no significant offsets in the stellar-mass TFR at both epochs. Furthermore, our intermediate redshift data allows a thorough analysis of subtle kinematical irregularities that trace stripping events, tidal processes, mergers, and their impact on different scaling relations at the epoch when half of the cluster mass has been already accreted. Finally, I will discuss the connection between the kinematic status of cluster galaxies and their recent star formation history.
We use different representations of the Tully-Fisher relation (TFR) to investigate quantitatively the evolutionary status of galaxies in two clusters at z~0.5 and 1.4, respectively, using ESO-VIMOS and FORS2 spectra. While the B-band TFR is sensitive to recent star-formation episodes, the stellar-mass TFR tracks the overall evolution of the underlying stellar population. The combination of these two schemes allows us to identify galaxies that might be suffering cluster-specific interactions as outliers in the B-band TFR, while these very same galaxies display no significant offsets in the stellar-mass TFR at both epochs. Furthermore, our intermediate redshift data allows a thorough analysis of subtle kinematical irregularities that trace stripping events, tidal processes, mergers, and their impact on different scaling relations at the epoch when half of the cluster mass has been already accreted. Finally, I will discuss the connection between the kinematic status of cluster galaxies and their recent star formation history.
Effects of Galaxy Interactions on SFR and AGN Activity out to z ~ 2.8
Interacting galaxies may not follow galaxy scaling relations for a relatively short time-scale. Galaxy interactions act as perturbations to the galaxy system, providing an opportunity to study galaxy evolution under slightly different conditions. By probing the response of the system to these perturbations, i.e. by comparing the evolution of interacting galaxies with that of the non-interacting galaxies, i.e. by quantifying the effects of galaxy interactions, their correlations with one another, their time-scale/merger-stage and redshift dependence, we can have a deeper understanding of the processes taking place during the galaxy evolution. I will present the enhancement in AGN activity and SFR due to galaxy interactions for the largest known sample of spectroscopically confirmed galaxy pairs at 0 < z < 2.8 by using deep multiwavelength observations from the COSMOS and the CANDELS surveys. I will also present how enhancements depend on redshift and relative masses of the galaxies.
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Interacting galaxies may not follow galaxy scaling relations for a relatively short time-scale. Galaxy interactions act as perturbations to the galaxy system, providing an opportunity to study galaxy evolution under slightly different conditions. By probing the response of the system to these perturbations, i.e. by comparing the evolution of interacting galaxies with that of the non-interacting galaxies, i.e. by quantifying the effects of galaxy interactions, their correlations with one another, their time-scale/merger-stage and redshift dependence, we can have a deeper understanding of the processes taking place during the galaxy evolution. I will present the enhancement in AGN activity and SFR due to galaxy interactions for the largest known sample of spectroscopically confirmed galaxy pairs at 0 < z < 2.8 by using deep multiwavelength observations from the COSMOS and the CANDELS surveys. I will also present how enhancements depend on redshift and relative masses of the galaxies.
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Constraining Ultra-Light Axions with Fuzzy Dark Matter Modelling and the Peak Patch Algorithm
Axions are a well-motivated dark matter candidate proposed as a solution to the strong CP-problem of QCD. Ultra-light axions (ULAs) present high energy physics models with a mass $m_a \lesssim 10^{-22}$ eV are studied with large-scale structure simulations based on the Peak Patch algorithm. The suppression of structure resulting from the ULAs' large Compton wavelength is modelled using a quantum potential resulting from a solitonic density profile on small scales. Implementing structure halo formation within Peak Patch will allow for direct comparisons of small-scale structure constraints with observations, like those from the Lyman alpha forest and weak lensing.
Axions are a well-motivated dark matter candidate proposed as a solution to the strong CP-problem of QCD. Ultra-light axions (ULAs) present high energy physics models with a mass $m_a \lesssim 10^{-22}$ eV are studied with large-scale structure simulations based on the Peak Patch algorithm. The suppression of structure resulting from the ULAs' large Compton wavelength is modelled using a quantum potential resulting from a solitonic density profile on small scales. Implementing structure halo formation within Peak Patch will allow for direct comparisons of small-scale structure constraints with observations, like those from the Lyman alpha forest and weak lensing.