The Phase Space and Stellar Populations of Cluster Galaxies at z ~ 1: Simultaneous Constraints on the Location and Timescale of Satellite Quenching

We investigate the velocity vs. position phase space of z ~ 1 cluster galaxies using a set of 424 spectroscopic redshifts in 9 clusters drawn from the GCLASS survey. Dividing the galaxy population into three categories: quiescent, star-forming, and poststarburst, we find that these populations have distinct distributions in phase space. Most striking are the poststarburst galaxies, which are commonly found at small clustercentric radii with high clustercentric velocities, and appear to trace a coherent ``ring" in phase space. Using several zoom simulations of clusters we show that the coherent distribution of the poststarbursts can be reasonably well-reproduced using a simple quenching scenario. Specifically, the phase space is best reproduced if satellite quenching occurs on a rapid timescale (0.1 < tau_{Q} < 0.5 Gyr) after galaxies make their first passage of R ~ 0.5R_{200}, a process that takes a total time of ~ 1 Gyr after first infall. We compare this quenching timescale to the timescale implied by the stellar populations of the poststarburst galaxies and find that the poststarburst spectra are well-fit by a rapid quenching (tau_{Q} = 0.4^{+0.3}_{-0.4} Gyr) of a typical star-forming galaxy. The similarity between the quenching timescales derived from these independent indicators is a strong consistency check of the quenching model. Given that the model implies satellite quenching is rapid, and occurs well within R_{200}, this would suggest that ram-pressure stripping of either the hot or cold gas component of galaxies are the most plausible candidates for the physical mechanism. The high cold gas consumption rates at z ~ 1 make it difficult to determine if hot or cold gas stripping is dominant; however, measurements of the redshift evolution of the satellite quenching timescale and location may be capable of distinguishing between the two.Comment: 10 pages, 4 figures, submitted to the Ap

Galaxy And Mass Assembly (GAMA): bulge-disc decomposition of KiDS data in the nearby Universe

We derive single Sérsic fits and bulge-disc decompositions for 13 096 galaxies at redshifts z \u3c 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 \u3e90 per cent role= presentation style= box-sizing: border-box; margin: 0px; padding: 0px; border: 0px; font-variant: inherit; font-stretch: inherit; line-height: normal; font-family: inherit; vertical-align: baseline; display: inline; word-spacing: normal; overflow-wrap: normal; white-space: nowrap; float: none; direction: ltr; max-width: none; max-height: none; min-width: 0px; min-height: 0px; position: relative; \u3e\u3e90 per cent\u3e90 per cent 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

The SAMI Galaxy Survey: The link between angular momentum and optical morphology

We investigate the relationship between stellar and gas specific angular momentum j, stellar massM* and optical morphology for a sample of 488 galaxies extracted from the Sydney-AAO Multi-object Integral field Galaxy Survey.We find that j, measured within one effective radius, monotonically increases with M* and that, for M* > 109.5 M⊙, the scatter in this relation strongly correlates with optical morphology (i.e. visual classification and Sérsic index). These findings confirm that massive galaxies of all types lie on a plane relating mass, angular momentum and stellar-light distribution, and suggest that the large-scale morphology of a galaxy is regulated by its mass and dynamical state. We show that the significant scatter in the M*-j relation is accounted for by the fact that, at fixed stellar mass, the contribution of ordered motions to the dynamical support of galaxies varies by at least a factor of 3. Indeed, the stellar spin parameter (quantified via λR) correlates strongly with Sérsic and concentration indices. This correlation is particularly strong once slow rotators are removed from the sample, showing that late-type galaxies and early-type fast rotators form a continuous class of objects in terms of their kinematic properties

The SAMI Galaxy Survey: Quenching of Star Formation in Clusters I. Transition Galaxies

We use integral-field spectroscopy from the SAMI Galaxy Survey to identify galaxies that show evidence of recent quenching of star formation. The galaxies exhibit strong Balmer absorption in the absence of ongoing star formation in more than 10% of their spectra within the SAMI field of view. These Hd-strong (HDS) galaxies (HDSGs) are rare, making up only similar to 2% (25/1220) of galaxies with stellar mass log(M-*/M-circle dot) &gt; 10. The HDSGs make up a significant fraction of nonpassive cluster galaxies (15%; 17/115) and a smaller fraction (2.0%; 8/387) of the nonpassive population in low-density environments. The majority (9/17) of cluster HDSGs show evidence of star formation at their centers, with the HDS regions found in the outer parts of the galaxy. Conversely, the HDS signal is more evenly spread across the galaxy for the majority (6/8) of HDSGs in low-density environments and is often associated with emission lines that are not due to star formation. We investigate the location of the HDSGs in the clusters, finding that they are exclusively within 0.6R(200) of the cluster center and have a significantly higher velocity dispersion relative to the cluster population. Comparing their distribution in projected phase space to those derived from cosmological simulations indicates that the cluster HDSGs are consistent with an infalling population that has entered the central 0.5r(200,3D) cluster region within the last similar to 1 Gyr. In the eight of nine cluster HDSGs with central star formation, the extent of star formation is consistent with that expected of outside-in quenching by ram pressure stripping. Our results indicate that the cluster HDSGs are currently being quenched by ram pressure stripping on their first passage through the cluster

The SAMI Galaxy Survey : rules of behaviour for spin-ellipticity radial tracks in galaxies

We study the behaviour of the spin-ellipticity radial tracks for 507 galaxies from the Sydney AAO Multiobject Integral Field (SAMI) Galaxy Survey with stellar kinematics out to >= 1.5R(e). We advocate for a morpho-dynamical classification of galaxies, relying on spatially resolved photometric and kinematic data. We find the use of spin-ellipticity radial tracks is valuable in identifying substructures within a galaxy, including embedded and counter-rotating discs, that are easily missed in unilateral studies of the photometry alone. Conversely, bars are rarely apparent in the stellar kinematics but are readily identified on images. Consequently, we distinguish the spin-ellipticity radial tracks of seven morpho-dynamical types: elliptical, lenticular, early spiral, late spiral, barred spiral, embedded disc, and 2 sigma galaxies. The importance of probing beyond the inner radii of galaxies is highlighted by the characteristics of galactic features in the spin-ellipticity radial tracks present at larger radii. The density of information presented through spin-ellipticity radial tracks emphasizes a clear advantage to representing galaxies as a track, rather than a single point, in spin-ellipticity parameter space.Peer reviewe

The SAMI Galaxy Survey: Bayesian Inference for Gas Disk Kinematics using a Hierarchical Gaussian Mixture Model

We present a novel Bayesian method, referred to as Blobby3D, to infer gas kinematics that mitigates the effects of beam smearing for observations using Integral Field Spectroscopy (IFS). The method is robust for regularly rotating galaxies despite substructure in the gas distribution. Modelling the gas substructure within the disk is achieved by using a hierarchical Gaussian mixture model. To account for beam smearing effects, we construct a modelled cube that is then convolved per wavelength slice by the seeing, before calculating the likelihood function. We show that our method can model complex gas substructure including clumps and spiral arms. We also show that kinematic asymmetries can be observed after beam smearing for regularly rotating galaxies with asymmetries only introduced in the spatial distribution of the gas. We present findings for our method applied to a sample of 20 star-forming galaxies from the SAMI Galaxy Survey. We estimate the global H$\alpha$ gas velocity dispersion for our sample to be in the range $\bar{\sigma}_v \sim$[7, 30] km s$^{-1}$. The relative difference between our approach and estimates using the single Gaussian component fits per spaxel is $\Delta \bar{\sigma}_v / \bar{\sigma}_v = - 0.29 \pm 0.18$ for the H$\alpha$ flux-weighted mean velocity dispersion.Comment: 23 pages, 12 figures, accepted for MNRA

The SAMI Galaxy Survey : mass as the driver of the kinematic morphology - density relation in clusters

We examine the kinematic morphology of early-type galaxies (ETGs) in eight galaxy clusters in the Sydney-AAO Multi-object Integral-field spectrograph Galaxy Survey. The clusters cover a mass range of 14.2log(M200/M☉) <15.2 and we measure spatially resolved stellar kinematics for 315 member galaxies with stellar masses 10.0 < log(M*/M☉) ≤ 11.7 within 1 R 200 of the cluster centers. We calculate the spin parameter, λ R , and use this to classify the kinematic morphology of the galaxies as fast or slow rotators (SRs). The total fraction of SRs in the ETG population is F SR = 0.14 ± 0.02 and does not depend on host cluster mass. Across the eight clusters, the fraction of SRs increases with increasing local overdensity. We also find that the slow-rotator fraction increases at small clustercentric radii (R cl < 0.3 R 200), and note that there is also an increase in the slow-rotator fraction at R cl ~ 0.6 R 200. The SRs at these larger radii reside in the cluster substructure. We find that the strongest increase in the slow-rotator fraction occurs with increasing stellar mass. After accounting for the strong correlation with stellar mass, we find no significant relationship between spin parameter and local overdensity in the cluster environment. We conclude that the primary driver for the kinematic morphology–density relationship in galaxy clusters is the changing distribution of galaxy stellar mass with the local environment. The presence of SRs in the substructure suggests that the cluster kinematic morphology–density relationship is a result of mass segregation of slow-rotating galaxies forming in groups that later merge with clusters and sink to the cluster center via dynamical friction.Publisher PDFPeer reviewe

The SAMI Galaxy Survey: rules of behaviour for spin-ellipticity radial tracks in galaxies

We study the behaviour of the spin-ellipticity radial tracks for 507 galaxies from the Sydney AAO Multiobject Integral Field (SAMI) Galaxy Survey with stellar kinematics out to ≥1.5Re. We advocate for a morpho-dynamical classification of galaxies, relying on spatially resolved photometric and kinematic data. We find the use of spin-ellipticity radial tracks is valuable in identifying substructures within a galaxy, including embedded and counter-rotating discs, that are easily missed in unilateral studies of the photometry alone. Conversely, bars are rarely apparent in the stellar kinematics but are readily identified on images. Consequently, we distinguish the spin-ellipticity radial tracks of seven morpho-dynamical types: elliptical, lenticular, early spiral, late spiral, barred spiral, embedded disc, and 2σ galaxies. The importance of probing beyond the inner radii of galaxies is highlighted by the characteristics of galactic features in the spin-ellipticity radial tracks present at larger radii. The density of information presented through spin-ellipticity radial tracks emphasizes a clear advantage to representing galaxies as a track, rather than a single point, in spin-ellipticity parameter space.This research was conducted by the Australian Research Council Centre of Excellence for All Sky Astrophysics in 3 Dimensions (ASTRO 3D), through project number CE170100013. The SAMI Galaxy Survey is based on observations made at the AngloAustralian Telescope. The Sydney-AAO Multi-object Integral field spectrograph (SAMI) was developed jointly by the University of Sydney and the Australian Astronomical Observatory. The SAMI input catalogue is based on data taken from the Sloan Digital Sky Survey, the GAMA Survey and the VST ATLAS Survey. The SAMI Galaxy Survey is supported by the Australian Research Council Centre of Excellence for All Sky Astrophysics in 3 Dimensions (ASTRO 3D), through project number CE170100013, the Australian Research Council Centre of Excellence for All-sky Astrophysics (CAASTRO), through project number CE110001020, and other participating institutions. The SAMI Galaxy Survey website is http://sami-survey.org/. JJB acknowledges support of an Australian Research Council Future Fellowship (FT180100231). JBH is supported by an ARC Laureate Fellowship that funds Jesse van de Sande and an ARC Federation Fellowship that funded the SAMI prototype. SKY acknowledges support from the Korean National Research Foundation (2017R1A2A1A05001116). MSO acknowledges the funding support from the Australian Research Council through a Future Fellowship (FT140100255). SB acknowledges the funding support from the Australian Research Council through a Future Fellowship (FT140101166). Support for AMM is provided by NASA through Hubble Fellowship grant #HST-HF2-51377 awarded by the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Inc., for NASA, under contract NAS5-26555