The study of low surface brightness light in large, deep imaging surveys is still uncharted territory as automated data reduction pipelines over-subtract or eliminate this light. Using archival data of the A85 cluster of galaxies taken with the Hyper Suprime-Cam on the Subaru Telescope, we show that using careful data processing can unveil the diffuse light within the cluster, the intracluster light. We reach surface brightness limits of (3σ, 10″ × 10″) = 30.9 and (3σ, 10″ × 10″) = 29.7 mag arcsec−2. We measured the radial surface brightness profiles of the brightest cluster galaxy out to the intracluster light (radius ∼215 kpc) for the g and i bands. We found that both the surface brightness and the color profiles become shallower beyond ∼75 kpc suggesting that a distinct component, the intracluster light, starts to dominate at that radius. The color of the profile at ∼100 kpc suggests that the buildup of the intracluster light of A85 occurs by the stripping of massive (∼1010 M ⊙) satellites. The measured fraction of this light ranges from 8%–30% in g, depending on the definition of intracluster light chosen.

We examine the stellar population radial gradients (age, metallicity, and [α/Fe]) of 96 passive central galaxies up to ∼2 R e in the SAMI Galaxy Survey. The targeted groups have a halo mass range of . The main goal of this work is to determine whether central galaxies have different stellar population properties when compared to similarly massive satellite galaxies. For the whole sample, we find negative metallicity radial gradients, which show evidence of becoming shallower with increasing stellar mass. The age and [α/Fe] gradients are slightly positive and consistent with zero, respectively. The [α/Fe] gradients become more negative with increasing mass, while the age gradients do not show any significant trend with mass. We do not observe a significant difference between the stellar population gradients of central and satellite galaxies at fixed stellar mass. The mean metallicity gradients are for central galaxies and for satellites. The mean age and [α/Fe] gradients are consistent between central and satellite galaxies, within the uncertainties, with a mean value of for centrals and for satellites and for centrals and for satellites. The stellar population gradients of central and satellite galaxies show no difference as a function of halo mass. This evidence suggests that the inner regions of central passive galaxies form in a similar fashion to those of satellite passive galaxies, in agreement with a two-phase formation scenario.

Dynamical models are crucial for uncovering the internal dynamics of galaxies; however, most of the results to date assume axisymmetry, which is not representative of a significant fraction of massive galaxies. Here, we build triaxial Schwarzschild 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 109.5–1012 M ⊙. We find that the changes in internal structures within 1R e are correlated with the total stellar mass of the individual galaxies. The majority of the galaxies in the sample (73% ± 3%) are oblate, while 19% ± 3% are mildly triaxial and 8% ± 2% have triaxial/prolate shape. Galaxies with log M ⋆ / M ⊙ > 10.50 are more likely to be non-oblate. We find a mean dark matter fraction of f DM = 0.28 ± 0.20, within 1R e. Galaxies with higher intrinsic ellipticity (flatter) are found to have more negative velocity anisotropy β r (tangential anisotropy). β r also shows an anticorrelation with the edge-on spin parameter λ Re , EO , so that β r decreases with increasing λ Re , EO , reflecting the contribution from disk-like orbits in flat, fast-rotating galaxies. 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.

In the past 15 years, the triaxial Schwarzschild orbit-superposition code developed by van den Bosch and van de Ven in Leiden has been widely applied to study the dynamics of galaxies. Recently, a bug was reported in the orbit calculation of this code, specifically in the mirroring procedure that is used to speed up the computation. We have fixed the incorrect mirroring in the DYNAMITE code, which is the publicly-released successor of the Leiden triaxial Schwarzschild code. In this study, we provide a thorough quantification of how this bug has affected the results of dynamical analyses performed with this code. We compare results obtained with the original and corrected versions of DYNAMITE, and discuss the differences in the phase-space distribution of a single orbit and in the global stellar orbit distribution, in the mass estimate of the central black hole in the highly triaxial galaxy PGC 46832, and in the measurement of intrinsic shape and enclosed mass for more than 50 galaxies. Focusing on the typical scientific applications of the Schwarzschild method, in all our tests we find that differences are negligible with respect to the statistical and systematic uncertainties. We conclude that previous results with the Leiden triaxial Schwarzschild code are not significantly affected by the incorrect mirroring.

Most dynamical models of galaxies to date assume axisymmetry, which is not representative of a significant fraction of massive galaxies. We have built triaxial orbit-superposition Schwarzschild models of galaxies observed by the SAMI Galaxy Survey, in order to reconstruct their inner orbital structure and mass distribution. The sample consists of 153 passive galaxies with total stellar masses in the range 109.5 to 1012 M⊙. We present an analysis of the internal structures and intrinsic properties of these galaxies as a function of their environment. We measure their environment using three proxies: central or satellite designation, halo mass and local 5th nearest neighbour galaxy density. We find that although these intrinsic properties correlate most strongly with stellar mass, environment does play a secondary role: at fixed stellar mass, galaxies in the densest regions are more radially anisotropic. In addition, central galaxies, and galaxies in high local densities show lower values of edge-on spin parameter proxy λRe, EO. We also find suggestions of a possible trend of the fractions of orbits with environment for lower-mass galaxies (between 109.5 and 1011 M⊙) such that, at fixed stellar mass, galaxies in higher local densities and halo mass have higher fractions of hot orbits and lower fractions of warm orbits. Our results demonstrate that after stellar mass, environment does play a role in shaping present-day passive galaxies.

We study environmental quenching using the spatial distribution of current star-formation and stellar population ages with the full SAMI Galaxy Survey. By using a star-formation concentration index [C-index, defined as log10(r50, Hα/r50, cont)], we separate our sample into regular galaxies (C-index≥−0.2) and galaxies with centrally concentrated star-formation (SF-concentrated; C-index < −0.2). Concentrated star-formation is a potential indicator of galaxies currently undergoing ‘outside-in’ quenching. Our environments cover ungrouped galaxies, low-mass groups (M200 ≤ 1012.5M⊙), high-mass groups (M200 in the range 1012.5 − 14M⊙) and clusters (M200 > 1014M⊙). We find the fraction of SF-concentrated galaxies increases as halo mass increases with 9 ± 2 per cent, 8 ± 3 per cent, 19 ± 4 per cent and 29 ± 4 per cent for ungrouped galaxies, low-mass groups, high-mass groups and clusters, respectively. We interpret these results as evidence for ‘outside-in’ quenching in groups and clusters. To investigate the quenching time-scale in SF-concentrated galaxies, we calculate light-weighted age (AgeL) and mass-weighted age (AgeM) using full spectral fitting, as well as the Dn4000 and HδA indices. We assume that the average galaxy age radial profile before entering a group or cluster is similar to ungrouped regular galaxies. At large radius (1–2 Re), SF-concentrated galaxies in high-mass groups have older ages than ungrouped regular galaxies with an age difference of 1.83 ± 0.38 Gyr for AgeL and 1.34 ± 0.56 Gyr for AgeM. This suggests that while ‘outside-in’ quenching can be effective in groups, the process will not quickly quench the entire galaxy. In contrast, the ages at 1-2 Re of cluster SF-concentrated galaxies and ungrouped regular galaxies are consistent (difference of 0.19 ±0.21 Gyr for AgeL, 0.40 ± 0.61 Gyr for AgeM), suggesting the quenching process must be rapid.

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