arXiv subjects

Sarah Brough

Publications and source records attributed to Sarah Brough.

At least 55 records · Page 3Linked to original sources

arXiv2022

Galaxy And Mass Assembly (GAMA): Bulge-disk decomposition of KiDS data in the nearby universe

We derive single Sérsic fits and bulge-disk decompositions for 13096 galaxies at redshifts z < 0.08 in the GAMA II equatorial survey regions in the Kilo-Degree Survey (KiDS) g, r and i bands. The surface brightness fitting is performed using the Bayesian two-dimensional profile fitting code ProFit. We fit three models to each galaxy in each band independently with a fully automated Markov-chain Monte Carlo analysis: a single Sérsic model, a Sérsic plus exponential and a point source plus exponential. After fitting the galaxies, we perform model selection and flag galaxies for which none of our models are appropriate (mainly mergers/Irregular galaxies). The fit quality is assessed by visual inspections, comparison to previous works, comparison of independent fits of galaxies in the overlap regions between KiDS tiles and bespoke simulations. The latter two are also used for a detailed investigation of systematic error sources. We find that our fit results are robust across various galaxy types and image qualities with minimal biases. Errors given by the MCMC underestimate the true errors typically by factors 2-3. Automated model selection criteria are accurate to > 90 % as calibrated by visual inspection of a subsample of galaxies. We also present g-r component colours and the corresponding colour-magnitude diagram, consistent with previous works despite our increased fit flexibility. Such reliable structural parameters for the components of a diverse sample of galaxies across multiple bands will be integral to various studies of galaxy properties and evolution. All results are integrated into the GAMA database.

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arXiv2022

The SAMI galaxy survey: galaxy size can explain the offset between star-forming and passive galaxies in the mass-metallicity relationship

In this work, we investigate how the central stellar metallicity ([Z/H]) of 1363 galaxies from the SAMI galaxy survey is related to their stellar mass and a proxy for the gravitational potential, $Φ$ = log10(M/M*) - log10($r_e$/kpc). In agreement with previous studies, we find that passive and star-forming galaxies occupy different areas of the [Z/H]-M* plane, with passive galaxies having higher [Z/H] than star-forming galaxies at fixed mass (a difference of 0.23 dex at log10(M/M*)=10.3). We show for the first time that all galaxies lie on the same relation between [Z/H] and $Φ$, and show that the offset in [Z/H] between passive and star-forming galaxies at fixed $Φ$ is smaller than or equal to the offset in [Z/H] at fixed mass (an average $Δ$[Z/H] of 0.11 dex at fixed $Φ$ compared to 0.21 dex at fixed mass). We then build a simple model of galaxy evolution to explain and understand our results. By assuming that [Z/H] traces $Φ$ over cosmic time and that the probability that a galaxy quenches depends on both its mass and size, we are able to reproduce these offsets in stellar metallicity with a model containing instantaneous quenching. We therefore conclude that an offset in metallicity at fixed mass cannot by itself be used as evidence of slow quenching processes, in contrast to previous studies. Instead, our model implies that metal-rich galaxies have always been the smallest objects for their mass in a population. Our findings reiterate the need to consider galaxy size when studying stellar populations.

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arXiv2022

The SAMI Galaxy Survey: The relationship between galaxy rotation and the motion of neighbours

Using data from the SAMI Galaxy Survey, we investigate the correlation between the projected stellar kinematic spin vector of 1397 SAMI galaxies and the line-of-sight motion of their neighbouring galaxies. We calculate the luminosity-weighted mean velocity difference between SAMI galaxies and their neighbours in the direction perpendicular to the SAMI galaxies angular momentum axes. The luminosity-weighted mean velocity offsets between SAMI and neighbours, which indicates the signal of coherence between the rotation of the SAMI galaxies and the motion of neighbours, is 9.0 $\pm$ 5.4 km s$^{-1}$ (1.7 $σ$) for neighbours within 1 Mpc. In a large-scale analysis, we find that the average velocity offsets increase for neighbours out to 2 Mpc. However, the velocities are consistent with zero or negative for neighbours outside 3 Mpc. The negative signals for neighbours at distance around 10 Mpc are also significant at $\sim 2$ $σ$ level, which indicate that the positive signals within 2 Mpc might come from the variance of large-scale structure. We also calculate average velocities of different subsamples, including galaxies in different regions of the sky, galaxies with different stellar masses, galaxy type, $λ_{Re}$ and inclination. Although low-mass, high-mass, early-type and low-spin galaxies subsamples show 2 - 3 $σ$ signal of coherence for the neighbours within 2 Mpc, the results for different inclination subsamples and large-scale results suggest that the $\sim 2 σ$ signals might result from coincidental scatter or variance of large-scale structure. Overall, the modest evidence of coherence signals for neighbouring galaxies within 2 Mpc needs to be confirmed by larger samples of observations and simulation studies.

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arXiv2022

The SAMI Galaxy Survey: The Link Between [$α$/Fe] and Kinematic Morphology

We explore a sample of 1492 galaxies with measurements of the mean stellar population properties and the spin parameter proxy, $λ_{R_{\rm{e}}}$, drawn from the SAMI Galaxy Survey. We fit a global $\left[α/\rm{Fe}\right]$-$σ$ relation, finding that $\left[α/\rm{Fe}\right]=(0.395\pm0.010)\rm{log}_{10}\left(σ\right)-(0.627\pm0.002)$. We observe an anti-correlation between the residuals $Δ\left[α/\rm{Fe}\right]$ and the inclination-corrected $λ_{\,R_{\rm{e}}}^{\rm{\,eo}}$, which can be expressed as $Δ\left[α/\rm{Fe}\right]=(-0.057\pm0.008)λ_{\,R_{\rm{e}}}^{\rm{\,eo}}+(0.020\pm0.003)$. The anti-correlation appears to be driven by star-forming galaxies, with a gradient of $Δ\left[α/\rm{Fe}\right]\sim(-0.121\pm0.015)λ_{\,R_{\rm{e}}}^{\rm{\,eo}}$, although a weak relationship persists for the subsample of galaxies for which star formation has been quenched. We take this to be confirmation that disk-dominated galaxies have an extended duration of star formation. At a reference velocity dispersion of 200 km s$^{-1}$, we estimate an increase in half-mass formation time from $\sim$0.5 Gyr to $\sim$1.2 Gyr from low- to high-$λ_{\,R_{\rm{e}}}^{\rm{\,eo}}$ galaxies. Slow rotators do not appear to fit these trends. Their residual $α$-enhancement is indistinguishable from other galaxies with $λ_{\,R_{\rm{e}}}^{\rm{\,eo}}\lessapprox0.4$, despite being both larger and more massive. This result shows that galaxies with $λ_{\,R_{\rm{e}}}^{\rm{\,eo}}\lessapprox0.4$ experience a similar range of star formation histories, despite their different physical structure and angular momentum.

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arXiv2022

Galapagos-2/Galfitm/GAMA -- multi-wavelength measurement of galaxy structure: separating the properties of spheroid and disk components in modern surveys

We present the capabilities of Galapagos--2 and Galfitm in the context of fitting 2-component profiles to galaxies, on the way to providing complete multi-band, multi-component fitting of large samples of galaxies in future surveys. We release both the code and the fit results to 234,239 objects from the DR3 of the Gama survey, a sample significantly deeper than previous works. We use stringent tests on both simulated and real data, as well as comparison to public catalogues to evaluate the advantages of using multi-band over single-band data. We show that multi-band fitting using Galfitm provides significant advantages when trying to decompose galaxies into their individual constituents, as more data are being used, by effectively being able to use the colour information buried in the individual exposures to its advantage. Using simulated data, we find that multi-band fitting significantly reduces the deviations from real parameter values, allows component sizes and Sérsic indices to be recovered more accurately, and, by design, constrains the band-to-band variations of these parameters to more physical values. On both simulated and real data, we confirm that the SEDs of the 2 main components can be recovered to fainter magnitudes compared to using single-band fitting, which tends to recover disks and bulges to - on average - have identical SEDs when the galaxies become too faint, instead of the different SEDs they truly have. By comparing our results to those provided by other fitting codes, we confirm that they agree in general, but measurement errors can be significantly reduced by using the multi-band tools developed by the MegaMorph project. We conclude that the multi-band fitting employed by Galapagos-2 and Galfitm significantly improves the accuracy of structural galaxy parameters and enables much larger samples to be be used in a scientific analysis.

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arXiv2022

Galaxy And Mass Assembly (GAMA): Data Release 4 and the z < 0.1 total and z < 0.08 morphological galaxy stellar mass functions

In Galaxy And Mass Assembly Data Release 4 (GAMA DR4), we make available our full spectroscopic redshift sample. This includes 248682 galaxy spectra, and, in combination with earlier surveys, results in 330542 redshifts across five sky regions covering ~250deg^2. The redshift density, is the highest available over such a sustained area, has exceptionally high completeness (95 per cent to r_KIDS=19.65mag), and is well suited for the study of galaxy mergers, galaxy groups, and the low redshift (z<0.25) galaxy population. DR4 includes 32 value-added tables or Data Management Units (DMUs) that provide a number of measured and derived data products including GALEX, ESO KiDS, ESO VIKING, WISE and Herschel Space Observatory imaging. Within this release, we provide visual morphologies for 15330 galaxies to z<0.08, photometric redshift estimates for all 18million objects to r_KIDS~25mag, and stellar velocity dispersions for 111830 galaxies. We conclude by deriving the total galaxy stellar mass function (GSMF) and its sub-division by morphological class (elliptical, compact-bulge and disc, diffuse-bulge and disc, and disc only). This extends our previous measurement of the total GSMF down to 10^6.75 M_sol h^-2_70 and we find a total stellar mass density of rho_*=(2.97+/-0.04)x10^8 M_sol h_70 Mpc^-3 or Omega_*=(2.17+/-0.03)x10^-3 h^-1_70. We conclude that at z<0.1, the Universe has converted 4.9+/-0.1 per cent of the baryonic mass implied by Big Bang Nucleosynthesis into stars that are gravitationally bound within the galaxy population.

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arXiv2022

An empirical measurement of the Halo Mass Function from the combination of GAMA DR4, SDSS DR12, and REFLEX II data

We construct the halo mass function (HMF) from the GAMA galaxy group catalogue over the mass range 10^12.7M_sol to 10^15.5M_sol, and find good agreement with the expectation from LambdaCDM. In comparison to previous studies, this result extends the mass range over which the HMF has now been measured over by an order of magnitude. We combine the GAMA DR4 HMF with similar data from the SDSS DR12 and REFLEX II surveys, and fit a four-parameter Murray-Robotham-Power (MRP) function, valid at z~0.1, yielding: a density normalisation of: log10 (phi Mpc^3)=-3.96[+0.55,-0.82], a high mass turn-over of: log10(M/M_sol)=14.13[+0.43,-0.40], a low mass power law slope of: alpha=-1.68[+0.21,-0.24] , and a high mass softening parameter of: beta= 0.63[+0.25,-0.11]. If we fold in the constraint on Omega_M from Planck 2018 Cosmology, we are able to reduce these uncertainties further, but this relies on the assumption that the power-law trend can be extrapolated from 10^12.7M_sol to zero mass. Throughout, we highlight the effort needed to improve on our HMF measurement: improved halo mass estimates that do not rely on calibration to simulations; reduced halo mass uncertainties needed to mitigate the strong Eddington Bias that arises from the steepness of the HMF low mass slope; and deeper wider area spectroscopic surveys. To our halo mass limit of 10^12.7 M_sol, we are directly resolving (`seeing') 41+/-5 per cent of the total mass density, i.e. Omega_[M>12.7]=0.128+/-0.016, opening the door for the direct construction of 3D dark matter mass maps at Mpc resolution.

astro-ph.CO↗

arXiv2022

The LEGA-C and SAMI Galaxy Surveys: Quiescent Stellar Populations and the Mass-Size Plane across 6 Gyr

We investigate the change in mean stellar population age and metallicity ([Z/H]) scaling relations for quiescent galaxies from intermediate redshift ($0.60\leq z\leq0.76$) using the LEGA-C Survey, to low redshift ($0.014\leq z\leq0.10$) using the SAMI Galaxy Survey. We find that, similarly to their low-redshift counterparts, the stellar metallicity of quiescent galaxies at $0.60\leq z\leq 0.76$ closely correlates with $M_*/R_\mathrm{e}$ (a proxy for the gravitational potential or escape velocity), in that galaxies with deeper potential wells are more metal-rich. This supports the hypothesis that the relation arises due to the gravitational potential regulating the retention of metals, by determining the escape velocity required by metal-rich stellar and supernova ejecta to escape the system and avoid being recycled into later stellar generations. On the other hand, we find no correlation between stellar age and $M_*/R_\mathrm{e}^2$ (stellar mass surface density $Σ$) in the LEGA-C sample, despite this being a strong relation at low redshift. We consider this change in the age--$Σ$ relation in the context of the redshift evolution of the star-forming and quiescent populations in the mass--size plane, and find our results can be explained as a consequence of galaxies forming more compactly at higher redshifts, and remaining compact throughout their evolution. Furthermore, galaxies appear to quench at a characteristic surface density that decreases with decreasing redshift. The $z\sim 0$ age--$Σ$ relation is therefore a result of building up the quiescent and star-forming populations with galaxies that formed at a range of redshifts and so a range of surface densities.

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arXiv2022

The SAMI Galaxy Survey: The internal orbital structure and mass distribution of passive galaxies from triaxial orbit-superposition Schwarzschild models

Dynamical models are crucial for uncovering the internal dynamics of galaxies, however, most of the results to date assume axisymmetry, which is not representative for a significant fraction of massive galaxies. Here, we build triaxial Schwarschild orbit-superposition models of galaxies taken from the SAMI Galaxy Survey, in order to reconstruct their inner orbital structure and mass distribution. The sample consists of 161 passive galaxies with total stellar masses in the range $10^{9.5}$ to $10^{12} M_{\odot}$. We find that the changes in internal structures within 1$R_{\rm e}$ are correlated with the total stellar mass of the individual galaxies. The majority of the galaxies in the sample ($73\% \pm 3\%$) are oblate, while $19\% \pm 3\%$ are mildly triaxial and $8\% \pm 2\%$ have triaxial/prolate shape. Galaxies with $\log M_{\star}/M_{\odot} > 10.50$ are more likely to be non-oblate. We find a mean dark matter fraction of $f_{\rm{DM}} = 0.28 \pm 0.20$, within 1$R_{\rm e}$. Galaxies with higher intrinsic ellipticity (flatter) are found to have more negative velocity anisotropy $β_r$ (tangential anisotropy). $β_r$ also shows an anti-correlation with the edge-on spin parameter \lam, so that $β_r$ decreases with increasing \lam. We see evidence of an increasing fraction of hot orbits with increasing stellar mass, while warm and cold orbits show a decreasing trend. We also find that galaxies with different ($V/σ$ - $h_3$) kinematic signatures have distinct combinations of orbits. These results are in agreement with a formation scenario in which slow- and fast-rotating galaxies form through two main channels.

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arXiv2022

The SAMI Galaxy Survey: the difference between ionised gas and stellar velocity dispersions

We investigate the mean locally-measured velocity dispersions of ionised gas ($σ_{\rm gas}$) and stars ($σ_*$) for 1090 galaxies with stellar masses $\log\,(M_*/M_{\odot}) \geq 9.5$ from the SAMI Galaxy Survey. For star-forming galaxies, $σ_*$ tends to be larger than $σ_{\rm gas}$, suggesting that stars are in general dynamically hotter than the ionised gas (asymmetric drift). The difference between $σ_{\rm gas}$ and $σ_*$ ($Δσ$) correlates with various galaxy properties. We establish that the strongest correlation of $Δσ$ is with beam smearing, which inflates $σ_{\rm gas}$ more than $σ_*$, introducing a dependence of $Δσ$ on both the effective radius relative to the point spread function and velocity gradients. The second-strongest correlation is with the contribution of active galactic nuclei (AGN) (or evolved stars) to the ionised gas emission, implying the gas velocity dispersion is strongly affected by the power source. In contrast, using the velocity dispersion measured from integrated spectra ($σ_{\rm aper}$) results in less correlation between the aperture-based $Δσ$ ($Δσ_{\rm aper}$) and the power source. This suggests that the AGN (or old stars) dynamically heat the gas without causing significant deviations from dynamical equilibrium. Although the variation of $Δσ_{\rm aper}$ is much smaller than that of $Δσ$, a correlation between $Δσ_{\rm aper}$ and gas velocity gradient is still detected, implying there is a small bias in dynamical masses derived from stellar and ionised gas velocity dispersions.

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arXiv2021

Galaxy and Mass Assembly (GAMA): The Weak Environmental Dependence of Quasar Activity at 0.1<z<0.35

Understanding the connection between nuclear activity and galaxy environment remains critical in constraining models of galaxy evolution. By exploiting extensive catalogued data from the Galaxy and Mass Assembly (GAMA) survey, we identify a representative sample of 205 quasars at 0.1 < z < 0.35 and establish a comparison sample of galaxies, closely matched to the quasar sample in terms of both stellar mass and redshift. On scales <1 Mpc, the galaxy number counts and group membership of quasars appear entirely consistent with those of the matched galaxy sample. Despite this, we find that quasars are ~1.5 times more likely to be classified as the group center, indicating a potential link between quasar activity and cold gas flows or galaxy interactions associated with rich group environments. On scales of ~a few Mpc, the clustering strength of both samples are statistically consistent and beyond 10 Mpc we find no evidence that quasars trace large scale structures any more than the galaxy control sample. Both populations are found to prefer intermediate-density sheets and filaments to either very high- or very low- density environments. This weak dependence of quasar activity on galaxy environment supports a paradigm in which quasars represent a phase in the lifetime of all massive galaxies and in which secular processes and a group-centric location are the dominant trigger of quasars at low redshift.

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arXiv2021

The SAMI Galaxy Survey: Mass and Environment as Independent Drivers of Galaxy Dynamics

The kinematic morphology-density relation of galaxies is normally attributed to a changing distribution of galaxy stellar masses with the local environment. However, earlier studies were largely focused on slow rotators; the dynamical properties of the overall population in relation to environment have received less attention. We use the SAMI Galaxy Survey to investigate the dynamical properties of $\sim$1800 early and late-type galaxies with $\log(M_*/M_{\odot})>9.5$ as a function of mean environmental overdensity ($Σ_{5}$) and their rank within a group or cluster. By classifying galaxies into fast and slow rotators, at fixed stellar mass above $\log(M_*/M_{\odot})>10.5$, we detect a higher fraction ($\sim3.4σ$) of slow rotators for group and cluster centrals and satellites as compared to isolated-central galaxies. Focusing on the fast-rotator population, we also detect a significant correlation between galaxy kinematics and their stellar mass as well as the environment they are in. Specifically, by using inclination-corrected or intrinsic $λ_{R_e}$ values, we find that, at fixed mass, satellite galaxies on average have the lowest $λ_{\,R_e,intr}$, isolated-central galaxies have the highest $λ_{\,R_e,intr}$, and group and cluster centrals lie in between. Similarly, galaxies in high-density environments have lower mean $λ_{\,R_e,intr}$ values as compared to galaxies at low environmental density. However, at fixed $Σ_{5}$, the mean $λ_{\,R_e,intr}$ differences for low and high-mass galaxies are of similar magnitude as when varying $Σ_{5}$ {($Δλ_{\,R_e,intr} \sim 0.05$. Our results demonstrate that after stellar mass, environment plays a significant role in the creation of slow rotators, while for fast rotators we also detect an independent, albeit smaller, impact of mass and environment on their kinematic properties.

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arXiv2021

Optimization of the Observing Cadence for the Rubin Observatory Legacy Survey of Space and Time: a pioneering process of community-focused experimental design

Vera C. Rubin Observatory is a ground-based astronomical facility under construction, a joint project of the National Science Foundation and the U.S. Department of Energy, designed to conduct a multi-purpose 10-year optical survey of the southern hemisphere sky: the Legacy Survey of Space and Time. Significant flexibility in survey strategy remains within the constraints imposed by the core science goals of probing dark energy and dark matter, cataloging the Solar System, exploring the transient optical sky, and mapping the Milky Way. The survey's massive data throughput will be transformational for many other astrophysics domains and Rubin's data access policy sets the stage for a huge potential users' community. To ensure that the survey science potential is maximized while serving as broad a community as possible, Rubin Observatory has involved the scientific community at large in the process of setting and refining the details of the observing strategy. The motivation, history, and decision-making process of this strategy optimization are detailed in this paper, giving context to the science-driven proposals and recommendations for the survey strategy included in this Focus Issue.

astro-ph.IM↗

arXiv2021

The SAMI Galaxy Survey: Trends in [α/Fe] as a Function of Morphology and Environment

We present a new set of index-based measurements of [$α$/Fe] for a sample of 2093 galaxies in the SAMI Galaxy Survey. Following earlier work, we fit a global relation between [$α$/Fe] and the galaxy velocity dispersion $σ$ for red sequence galaxies, [$α$/Fe]=(0.378$\pm$0.009)log($σ$/100)+(0.155$\pm$0.003). We observe a correlation between the residuals and the local environmental surface density, whereas no such relation exists for blue cloud galaxies. In the full sample, we find that elliptical galaxies in high-density environments are $α$-enhanced by up to 0.057$\pm$0.014 dex at velocity dispersions $σ$<100 km/s, compared with those in low-density environments. This $α$-enhancement is morphology-dependent, with the offset decreasing along the Hubble sequence towards spirals, which have an offset of 0.019$\pm$0.014 dex. At low velocity dispersion and controlling for morphology, we estimate that star formation in high-density environments is truncated $\sim1$ Gyr earlier than in low-density environments. For elliptical galaxies only, we find support for a parabolic relationship between [$α$/Fe] and $σ$, with an environmental $α$-enhancement of at least 0.03 dex. This suggests strong contributions from both environment and mass-based quenching mechanisms. However, there is no evidence for this behaviour in later morphological types.

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arXiv2021

Galaxy And Mass Assembly (GAMA) Survey: The Merging Potential of Brightest Group Galaxies

Using a volume-limited sample of 550 groups from the Galaxy And Mass Assembly (GAMA) Galaxy Group Catalogue spanning the halo mass range $12.8 < \log [M_{h}/M] < 14.2$, we investigate the merging potential of central Brightest Group Galaxies (BGGs). We use spectroscopically-confirmed close-companion galaxies as an indication of the potential stellar mass build-up of low-redshift BGGs, $z \leq 0.2$. We identify 17 close-companion galaxies with projected separations $r_{p} < 30$ kpc, relative velocities $Δv \leq 300$ km s$^{-1}$, and stellar-mass ratios $M_{BGG}/M_{CC} \leq 4$ relative to the BGG. These close-companion galaxies yield a total pair fraction of $0.03 \pm 0.01$. Overall, we find that BGGs in our sample have the potential to grow in stellar mass due to mergers by $2.2 \pm 1.5\%$ Gyr$^{-1}$. This is lower than the stellar mass growth predicted by current galaxy evolution models.

astro-ph.GA↗

arXiv2021

The SAMI Galaxy Survey: a statistical approach to an optimal classification of stellar kinematics in galaxy surveys

Large galaxy samples from multi-object IFS surveys now allow for a statistical analysis of the z~0 galaxy population using resolved kinematics. However, the improvement in number statistics comes at a cost, with multi-object IFS survey more severely impacted by the effect of seeing and lower S/N. We present an analysis of ~1800 galaxies from the SAMI Galaxy Survey and investigate the spread and overlap in the kinematic distributions of the spin parameter proxy $λ_{Re}$ as a function of stellar mass and ellipticity. For SAMI data, the distributions of galaxies identified as regular and non-regular rotators with \textsc{kinemetry} show considerable overlap in the $λ_{Re}$-$\varepsilon_e$ diagram. In contrast, visually classified galaxies (obvious and non-obvious rotators) are better separated in $λ_{Re}$ space, with less overlap of both distributions. Then, we use a Bayesian mixture model to analyse the observed $λ_{Re}$-$\log(M_*/M_{\odot})$ distribution. Below $\log(M_{\star}/M_{\odot})\sim10.5$, a single beta distribution is sufficient to fit the complete $λ_{Re}$ distribution, whereas a second beta distribution is required above $\log(M_{\star}/M_{\odot})\sim10.5$ to account for a population of low-$λ_{Re}$ galaxies. While the Bayesian mixture model presents the cleanest separation of the two kinematic populations, we find the unique information provided by visual classification of kinematic maps should not be disregarded in future studies. Applied to mock-observations from different cosmological simulations, the mixture model also predicts bimodal $λ_{Re}$ distributions, albeit with different positions of the $λ_{Re}$ peaks. Our analysis validates the conclusions from previous smaller IFS surveys, but also demonstrates the importance of using kinematic selection criteria that are dictated by the quality of the observed or simulated data.

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arXiv2021

VEGAS: A VST Early-type GAlaxy Survey.VI. The diffuse light in HCG 86 from the ultra-deep VEGAS images

Context. In this paper we present ultra deep images of the compact group of galaxies HCG 86 as part of the VEGAS survey. Aims. Our main goals are to estimate the amount of intragroup light (IGL), to study the light and color distributions in order to address the main formation process of the IGL component in groups of galaxies. Methods. We derived the azimuthally averaged surface brightness profiles in the g,r and i bands with g - r and r - i average colors and color profiles for all group members. By fitting the light distribution, we have extrapolated the contribution of the stellar halos plus the diffuse light from the brightest component of each galaxy. The results are compared with theoretical predictions. Results. The long integration time and wide area covered make our data deeper than previous literature studies of the IGL in compact groups of galaxies and allow us to produce an extended (~160 kpc) map of the IGL, down to a surface brightness level of about 30 mag/arcsec^2 in the g band. The IGL in HCG 86 is mainly in diffuse form and has average colors of g - r ~ 0.8 mag and r - i ~ 0.4 mag. The fraction of IGL in HCG 86 is ~ 16% of the total luminosity of the group, and this is consistent with estimates available for other compact groups and loose groups of galaxies of similar virial masses. A weak trend is present between the amount of IGL and the early-type to late-type galaxy ratio. Conclusions. By comparing the IGL fraction and colors with those predicted by simulations, the amount of IGL in HCG 86 would be the result of the disruption of satellites at an epoch of z ~ 0.4. At this redshift, observed colors are consistent with the scenario where the main contribution to the mass of the IGL comes from the intermediate-massive galaxies.

astro-ph.GA↗

arXiv2021

The SAMI Galaxy Survey: stellar population and structural trends across the Fundamental Plane

We study the Fundamental Plane (FP) for a volume- and luminosity-limited sample of 560 early-type galaxies from the SAMI survey. Using r-band sizes and luminosities from new Multi-Gaussian Expansion (MGE) photometric measurements, and treating luminosity as the dependent variable, the FP has coefficients a=1.294$\pm$0.039, b= 0.912$\pm$0.025, and zero-point c= 7.067$\pm$0.078. We leverage the high signal-to-noise of SAMI integral field spectroscopy, to determine how structural and stellar-population observables affect the scatter about the FP. The FP residuals correlate most strongly (8$σ$ significance) with luminosity-weighted simple-stellar-population (SSP) age. In contrast, the structural observables surface mass density, rotation-to-dispersion ratio, Sérsic index and projected shape all show little or no significant correlation. We connect the FP residuals to the empirical relation between age (or stellar mass-to-light ratio $Υ_\star$) and surface mass density, the best predictor of SSP age amongst parameters based on FP observables. We show that the FP residuals (anti-)correlate with the residuals of the relation between surface density and $Υ_\star$. This correlation implies that part of the FP scatter is due to the broad age and $Υ_\star$ distribution at any given surface mass density. Using virial mass and $Υ_\star$ we construct a simulated FP and compare it to the observed FP. We find that, while the empirical relations between observed stellar population relations and FP observables are responsible for most (75%) of the FP scatter, on their own they do not explain the observed tilt of the FP away from the virial plane.

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