Central Stellar Velocity Dispersion Research Articles

The Velocity Dispersion Function for Quiescent Galaxies in Massive Clusters from IllustrisTNG

We derive the central stellar velocity dispersion function (VDF) for quiescent galaxies in 280 massive clusters with log(M200/M⊙)>14 in IllustrisTNG300. The VDF is an independent tracer of the dark matter mass distribution of subhalos in galaxy clusters. Based on the IllustrisTNG cluster catalog, we select quiescent member subhalos with a specific star formation rate <2 × 10−11 yr−1 and stellar mass log(M*/M⊙)>9 . We then simulate fiber spectroscopy to measure the stellar velocity dispersion of the simulated galaxies; we compute the line-of-sight velocity dispersions of star particles within a cylindrical volume that penetrates the core of each subhalo. We construct the VDFs for quiescent subhalos within R 200. The simulated cluster VDF exceeds the simulated field VDF for logσ*>2.2 , indicating the preferential formation of large velocity dispersion galaxies in dense environments. The excess is similar in simulations and in the observations. We also compare the simulated VDF for the three most massive clusters with log(M200/M⊙)>15 with the observed VDF for the two most massive clusters in the local Universe, Coma and A2029. Intriguingly, the simulated VDFs are significantly lower for logσ*>2.0 . This discrepancy results from (1) a smaller number of subhalos with log(M*/M⊙)>10 in TNG300 compared to the observed clusters, and (2) a significant offset between the observed and simulated M *–σ * relations. The consistency in the overall shape of the observed and simulated VDFs offers a unique window into galaxy and structure formation in simulations.

Galaxies’ properties in the Fundamental Plane across time

Context. Using the Illustris-1 and IllustrisTNG-100 simulations, we investigate the properties of the Fundamental Plane (FP), which is the correlation between the effective radius Re, the effective surface intensity Ie, and the central stellar velocity dispersion σ of galaxies, at different cosmic epochs. Aims. Our aim is to study the properties of galaxies in the FP and its projections across time, adopting samples covering different intervals of mass. We would like to demonstrate that the position of a galaxy in the FP space strongly depends on its degree of evolution, which might be represented by the β and $ L^\prime_0 $ parameters entering the L = $ L^\prime_0 $ (t)σβ(t) law. Methods. Starting from the comparison of the basic relations among the structural parameters of artificial and real galaxies at low redshift, we obtain the fit of the FP and its coefficients at different cosmic epochs for samples of different mass limits. Then, we analyze the dependence of the galaxy position in the FP space as a function of the β parameter and the star formation rate (SFR). Results. We find that: (1) the coefficients of the FP change with the mass range of the galaxy sample; (2) the low luminous and less massive galaxies do not share the same FP of the bright massive galaxies; (3) the scatter around the fitted FP is quite small at any epoch and increases when the mass interval increases; (4) the distribution of galaxies in the FP space strongly depends on the β values (i.e., on the degree of virialization and the star formation rate). Conclusions. The FP is a complex surface that is well approximated by a plane only when galaxies share similar masses and condition of virialization.

Velocity Dispersions of Quiescent Galaxies in IllustrisTNG

We examine the central stellar velocity dispersion of subhalos based on IllustrisTNG cosmological hydrodynamic simulations. The central velocity dispersion is a fundamental observable that links galaxies with their dark matter subhalos. We carefully explore simulated stellar velocity dispersions derived with different definitions to assess possible systematics. We explore the impact of variation in the identification of member stellar particles, the viewing axes, the velocity dispersion computation technique, and simulation resolution. None of these issues impact the velocity dispersion significantly; any systematic uncertainties are smaller than the random error. We examine the stellar mass–velocity dispersion relation as an observational test of the simulations. At fixed stellar mass, the observed velocity dispersions significantly exceed the simulation results. This discrepancy is an interesting benchmark for the IllustrisTNG simulations because the simulations are not explicitly tuned to match this relation. We demonstrate that the stellar velocity dispersion provides measures of the dark matter velocity dispersion and the dark matter subhalo mass.

The SAMI galaxy survey: impact of black hole activity on galaxy spin–filament alignments

ABSTRACT The activity of central supermassive black holes might affect the alignment of galaxy spin axes with respect to the closest cosmic filaments. We exploit the Sydney–AAO Multi-object Integral-field Galaxy Survey to study possible relations between black hole activity and the spin–filament alignments of stars and ionized gas separately. To explore the impact of instantaneous black hole activity, active galaxies are selected according to emission-line diagnostics. Central stellar velocity dispersion (σc) is used as a proxy for black hole mass and its integrated activity. We find evidence for the gas spin–filament alignments to be influenced by AGN, with Seyfert galaxies showing a stronger perpendicular alignment at fixed bulge mass with respect to galaxies, where ionization is consequence of low-ionization nuclear emission-line regions (LINERs) or old stellar populations (retired galaxies). On the other hand, the greater perpendicular tendency for the stellar spin–filament alignments of high-bulge mass galaxies is dominated by retired galaxies. Stellar alignments show a stronger correlation with σc compared to the gas alignments. We confirm that bulge mass (Mbulge) is the primary parameter of correlation for both stellar and gas spin–filament alignments (with no residual dependency left for σc), while σc is the most important property for secular star formation quenching (with no residual dependency left for Mbulge). These findings indicate that Mbulge and σc are the most predictive parameters of two different galaxy evolution processes, suggesting mergers trigger spin–filament alignment flips and integrated black hole activity drives star formation quenching.

Dissect two-halo galactic conformity effect for central galaxies: the dependence of star formation activities on the large-scale environment

ABSTRACT We investigate the two-halo galactic conformity effect for central galaxies, which is the spatial correlation of the star formation activities for central galaxies to several Mpcs, by studying the dependence of the star formation activities of central galaxies on their large-scale structure in our local Universe using the SDSS data. Here we adopt a novel environment metric using only central galaxies quantified by the distance to the nth nearest central galaxy. This metric measures the environment within an aperture from ∼1 to ≳ 10 Mpc, with a median value of ∼4 Mpc. We found that two kinds of conformity effects in our local Universe. The first one is that low-mass central galaxies are more quenched in high-density regions, and we found that this effect mainly comes from low-mass centrals that are close to a more massive halo. A similar trend is also found in the IllustrisTNG simulation, which can be entirely explained by backsplash galaxies. The second conformity effect is that massive central galaxies in low-density regions are more star-forming. This population of galaxies also possesses a higher fraction of spiral morphology and lower central stellar velocity dispersion, suggesting that their low quiescent fraction is due to less-frequent major merger events experienced in the low-density regions and, as a consequence, less-massive bulges and central black holes.

BASS. XXVI. DR2 Host Galaxy Stellar Velocity Dispersions

We present new central stellar velocity dispersions for 484 Sy 1.9 and Sy 2 from the second data release of the Swift/BAT AGN Spectroscopic Survey (BASS DR2). This constitutes the largest study of velocity dispersion measurements in X-ray-selected obscured active galactic nuclei (AGN) with 956 independent measurements of the Ca ii H and K λ3969, 3934 and Mg I λ5175 region (3880–5550 Å) and the calcium triplet region (8350–8730 Å) from 642 spectra mainly from VLT/X-Shooter or Palomar/DoubleSpec. Our sample spans velocity dispersions of 40–360 km s1, corresponding to 4–5 orders of magnitude in black hole mass (M BH = 105.5−9.6 M ⊙), bolometric luminosity (L bol ∼ 1042–46 erg s−1), and Eddington ratio (L/L Edd ∼ 10−5 to 2). For 281 AGN, our data and analysis provide the first published central velocity dispersions, including six AGN with low-mass black holes (M BH = 105.5−6.5 M ⊙), discovered thanks to high spectral resolution observations (σ inst ∼ 25 km s−1). The survey represents a significant advance with a nearly complete census of velocity dispersions of hard X-ray–selected obscured AGN with measurements for 99% of nearby AGN (z < 0.1) outside the Galactic plane (∣b∣ > 10°). The BASS AGN have much higher velocity dispersions than the more numerous optically selected narrow-line AGN (i.e., ∼150 versus ∼100 km s−1) but are not biased toward the highest velocity dispersions of massive ellipticals (i.e., >250 km s−1). Despite sufficient spectral resolution to resolve the velocity dispersions associated with the bulges of small black holes (∼104–5 M ⊙), we do not find a significant population of super-Eddington AGN. Using estimates of the black hole sphere of influence from velocity dispersion, direct stellar and gas black hole mass measurements could be obtained with existing facilities for more than ∼100 BASS AGN.

Star-forming S0 Galaxies in SDSS-MaNGA: fading spirals or rejuvenated S0s?

ABSTRACTWe investigate the origin of rare star formation in an otherwise red-and-dead population of S0 galaxies, using spatially resolved spectroscopy. Our sample consists of 120 low redshift (z &amp;lt; 0.1) star-forming S0 (SF-S0) galaxies from the SDSS-IV MaNGA DR15. We have selected this sample after a visual inspection of deep images from the DESI Legacy Imaging Surveys DR9 and the Subaru/HSC-SSP survey PDR3 to remove contamination from spiral galaxies. We also construct two control samples of star-forming spirals (SF-Sps) and quenched S0s (Q-S0s) to explore their evolutionary link with the star-forming S0s. To study star formation at resolved scales, we use dust-corrected H α luminosity and stellar density (Σ⋆) maps to construct radial profiles of star formation rate (SFR) surface density (ΣSFR) and specific SFR (sSFR). Examining these radial profiles, we find that star formation in SF-S0s is centrally dominated as opposed to disc-dominated star formation in spirals. We also compared various global (size–mass relation, bulge-to-total luminosity ratio) and local (central stellar velocity dispersion) properties of SF-S0s to those of the control sample galaxies. We find that SF-S0s are structurally similar to the quenched S0s and are different from star-forming spirals. We infer that SF-S0s are unlikely to be fading spirals. Inspecting stellar and gas velocity maps, we find that more than $50{{\ \rm per\ cent}}$ of the SF-S0 sample shows signs of recent galaxy interactions such as kinematic misalignment, counter-rotation, and unsettled kinematics. Based on these results, we conclude that in our sample of SF-S0s, star formation has been rejuvenated, with minor mergers likely to be a major driver.

Tomography of the Ie-Re and L-Sigma Planes

We have analyzed the distribution of early-type galaxies (ETGs) in the effective surface intensity vs. effective radius (Ie−Re) plane and in the total luminosity vs. central stellar velocity dispersion (L−σ) diagram, with the aim of studying the physical variables that allow the transformation of one space-parameter into the other. We find that the classical Faber–Jackson relation L=L0σα, in which the parameters L0 and α are confined in a small range of possible values, is incompatible with the distribution observed in the Ie−Re plane. The two distributions become mutually consistent only if luminosity is not considered a pure proxy of mass but a variable tightly dependent on the past history of mass assembling and star formation and on the present evolutionary state of the stellar content of a galaxy. The solution comes by considering the L=L0′σβ law proposed by D’Onofrio et al. in 2020, in which both L0′ and β can vary considerably from galaxy to galaxy. We will also show that the data of the Illustris numerical simulation prove the physical foundation of the L=L0′σβ law and confirm the prediction of the Zone of Exclusion (ZoE) originating from the intersection of the virial law with the L=L0′σβ relation. The ZoE is the region in the Ie−Re and Re−Ms diagrams avoided by real galaxies, and the border of which marks the condition of ‘full’ virial equilibrium with no recent significant merger events and no undergoing star formation.

A photometric and kinematic analysis of UDG1137+16 (dw1137+16): Probing ultradiffuse galaxy formation in a group environment

ABSTRACT The dominant physical formation mechanism(s) for ultradiffuse galaxies (UDGs) is still poorly understood. Here, we combine new, deep imaging from the Jeanne Rich Telescope with deep integral field spectroscopy from the Keck II telescope to investigate the formation of UDG1137+16 (dw1137+16). Our new analyses confirm both its environmental association with the low density UGC 6594 group, along with its large size of 3.3 kpc and status as a UDG. The new imaging reveals two distinct stellar components for UDG1137+16, indicating that a central stellar body is surrounded by an outer stellar envelope undergoing tidal interaction. Both the components have approximately similar stellar masses. From our integral field spectroscopy, we measure a stellar velocity dispersion within the half-light radius (15 ± 4 km s−1) and find that UDG1137+16 is similar to some other UDGs in that it is likely dark matter dominated. Incorporating literature measurements, we also examine the current state of UDG observational kinematics. Placing these data on the central stellar velocity dispersion–stellar mass relation, we suggest there is little evidence for UDG1137+16 being created through a strong tidal interaction. Finally, we investigate the constraining power current dynamical mass estimates (from stellar and globular cluster velocity dispersions) have on the total halo mass of UDGs. As most are measured within the half-light radius, they are unable to accurately constrain UDG total halo masses.

Tracing Dark Matter Halos with Satellite Kinematics and the Central Stellar Velocity Dispersion of Galaxies

Abstract It has been suggested that the central stellar velocity dispersion of galaxies can trace dark matter halo mass directly. We test this hypothesis using a complete spectroscopic sample of isolated galaxies surrounded by faint satellite galaxies from the Sloan Digital Sky Survey Data Release 12. We apply a friends-of-friends algorithm with projected linking length and radial velocity linking length km s−1 to construct our sample. Our sample includes 2807 isolated galaxies with 3417 satellite galaxies at . We divide the sample into two groups based on the primary galaxy color: red and blue primary galaxies separated at . The central stellar velocity dispersions of the primary galaxies are proportional to the luminosities and stellar masses of the same galaxies. Stacking the sample based on the central velocity dispersion of the primary galaxies, we derive the velocity dispersions of their satellite galaxies, which trace the dark matter halo mass of the primary galaxies. The system velocity dispersion of the satellite galaxies shows a remarkably tight correlation with the central velocity dispersion of the primary galaxies for both red and blue samples. In particular, the slope of the relation is identical to 1 for red primary systems. This tight relation suggests that the central stellar velocity dispersion of galaxies is indeed an efficient and robust tracer for dark matter halo mass. We provide empirical relations between the central stellar velocity dispersion and the dark matter halo mass.

The Velocity Dispersion Function for Quiescent Galaxies in Nine Strong-lensing Clusters

Abstract We measure the central stellar velocity dispersion function for quiescent galaxies in a set of nine northern clusters in the redshift range 0.18 &lt; z &lt; 0.29 and with strong lensing arcs in Hubble Space Telescope images. The velocity dispersion function links galaxies directly to their dark matter halos. From dense SDSS and MMT/Hectospec spectroscopy, we identify 222–463 spectroscopic members in each cluster. We derive physical properties of cluster members including redshift, , and central stellar velocity dispersion and we include a table of these measurements for 3419 cluster members. We construct the velocity dispersion functions for quiescent galaxies with &gt; 1.5 and within R 200. The cluster velocity dispersion functions all show excesses at σ ≳ 250 km s−1 compared to the field velocity dispersion function. The velocity dispersion function slope at large velocity dispersion (σ &gt; 160 km s−1) is steeper for more massive clusters, consistent with the trend observed for cluster luminosity functions. The spatial distribution of galaxies with large velocity dispersion at radii larger than R 200 further underscores the probable major role of dry mergers in the growth of massive cluster galaxies during cluster assembly.

A robust two-parameter description of the stellar profile of elliptical galaxies

Context. The stellar density profile of a galaxy is typically summarised with two numbers: the total stellar mass and half-light radius. The total mass of a galaxy, however, is not a well-defined quantity, due to the finite depth of photometric observations and the arbitrariness of the distinction between galaxy and diffuse intra-group light. This limits our ability to make accurate comparisons between models and observations. Aims. I wish to provide a more robust two-parameter description of the stellar density distribution of elliptical galaxies, in terms of quantities that can be measured unambiguously. Methods. I propose using the stellar mass enclosed within 10 kpc in projection, M*,10, and the mass-weighted stellar density slope within the same aperture, Γ*,10, for this purpose. I measured the distribution in M*,10 and Γ*,10 of a sample of elliptical galaxies from the Sloan Digital Sky Survey and the Galaxy And Mass Assembly survey, using photometry from the Hyper Suprime-Cam survey. I measured, at fixed (M*,10, Γ*,10), what the spread is in the galaxy surface brightness profile and central stellar velocity dispersion within the sample. As a first application, I then compared the observed M*,10 − Γ*,10 relation of elliptical galaxies with that of similarly selected galaxies in the EAGLE REFERENCE simulation. Results. The pair of values of (M*,10, Γ*,10) can be used to predict the stellar density profile in the inner 10 kpc of a galaxy with better than 20% accuracy. Similarly, M*,10 and Γ*,10 can be combined to obtain a proxy for stellar velocity dispersion that is at least as good as the stellar mass fundamental plane. The average stellar density slope of EAGLE elliptical galaxies matches that of observed ones at M*,10 = 1011 M⊙ well, but the EAGLE M*,10 − Γ*,10 relation is shallower and has a larger intrinsic scatter compared to observations. Conclusions. This new parameterisation of the stellar density profile of massive elliptical galaxies provides a more robust way of comparing results from different photometric surveys and from hydrodynamical simulations, with respect to a description based on total stellar mass and half-light radius.

Infrared Emission from Cold Gas Dusty Disks in Massive Ellipticals

Abstract What is the expected infrared output of elliptical galaxies? We report the latest findings obtained in this high time resolution (∼10 yr) and high spatial resolution (2.5 pc at center) study. We add a set of grain physics to the Massive active galactic nucleus (AGN) Controlled Ellipticals Resolved code, including (a) dust grains made in passive stellar evolution; (b) dust grain growth due to collision and sticking; (c) grain destruction due to thermal sputtering; (d) dust cooling of hot gas via inelastic collisions; and (e) radiation pressure on dust grains. The code improvements enable us to analyze metal depletion and AGN obscuration due to dust, and to assess its infrared output. We simulate a representative massive elliptical galaxy of a central stellar velocity dispersion ∼260 km s−1 and modest rotation. We find that: (1) the circumnuclear disk (∼1 kpc in diameter) is dusty in its outer region where most of the metals are contained in dust grains, while in the inner disk, dust grains are mostly destroyed by the AGN irradiation; (2) the dusty disk is optically thick to both the starlight within the disk and the radiation from the central AGN; thus the AGN is obscured behind the disk, and the covering factor is ∼0.2; and (3) the duty cycles of the AGN activities, star formation, and the dust infrared luminosity roughly match observations; e.g., in most of its lifetime, the simulated galaxy is a stereotypical “quiescent” elliptical galaxy with , but it can reach ≳1046 erg s−1 during outbursts with a star formation rate .

Velocity Dispersions of Massive Quiescent Galaxies from Weak Lensing and Spectroscopy*

Abstract We use MMT spectroscopy and deep Subaru Hyper Suprime-Cam (HSC) imaging to compare the spectroscopic central stellar velocity dispersion of quiescent galaxies with the effective dispersion of the dark matter halo derived from the stacked lensing signal. The spectroscopic survey (the Smithsonian Hectospec Lensing Survey) provides a sample of 4585 quiescent galaxy lenses with measured line-of-sight central stellar velocity dispersion (σ SHELS) that is more than 85% complete for R &lt; 20.6, D n 4000 &gt; 1.5 and M ⋆ &gt; 109.5 M ⊙. The median redshift of the sample of lenses is 0.32. We measure the stacked lensing signal from the HSC deep imaging. The central stellar velocity dispersion is directly proportional to the velocity dispersion derived from the lensing σ Lens, . The independent spectroscopic and weak lensing velocity dispersions probe different scales, ∼3 kpc and ≳100 kpc, respectively, and strongly indicate that the observable central stellar velocity dispersion for quiescent galaxies is a good proxy for the velocity dispersion of the dark matter halo. We thus demonstrate the power of combining high-quality imaging and spectroscopy to shed light on the connection between galaxies and their dark matter halos.

The cosmic evolution of the stellar mass–velocity dispersion relation of early-type galaxies

ABSTRACT We study the evolution of the observed correlation between central stellar velocity dispersion σe and stellar mass M* of massive ($M_*\gtrsim 3\times 10^{10}\, \mathrm{M_\odot}$) early-type galaxies (ETGs) out to redshift z ≈ 2.5, taking advantage of a Bayesian hierarchical inference formalism. Collecting ETGs from state-of-the-art literature samples, we build a fiducial sample (0 ≲ z ≲ 1), which is obtained with homogeneous selection criteria, but also a less homogeneous extended sample (0 ≲ z ≲ 2.5). Based on the fiducial sample, we find that at z ≲ 1 the M*–σe relation is well represented by $\sigma _{\mathrm{e}}\propto M_*^{\beta }(1+z)^{\zeta}$, with β ≃ 0.18 independent of redshift and ζ ≃ 0.4 (at a given M*, σe decreases for decreasing z, for instance by a factor of ≈1.3 from z = 1 to z = 0). When the slope β is allowed to evolve, we find it increasing with redshift: β(z) ≃ 0.16 + 0.26log (1 + z) describes the data as well as constant β ≃ 0.18. The intrinsic scatter of the M*–σe relation is ≃0.08 dex in σe at given M*, independent of redshift. Our results suggest that, on average, the velocity dispersion of individual massive (M* ≳ 3 × 1011M⊙) ETGs decreases with time while they evolve from z ≈ 1 to z ≈ 0. The analysis of the extended sample, over the wider redshift range 0 ≲ z ≲ 2.5, leads to results similar to that of the fiducial sample, with slightly stronger redshift dependence of the normalization (ζ ≃ 0.5) and weaker redshift dependence of the slope (dβ/dlog (1 + z) ≃ 0.18) when β varies with time. At z = 2 ETGs with $M_*\approx 10^{11}\, \mathrm{M_\odot}$ have, on average, ≈1.7 higher σe than ETGs of similar stellar mass at z = 0.

A Black Hole Feedback Valve in Massive Galaxies

Abstract Star formation in the universe’s most massive galaxies proceeds furiously early in time but then nearly ceases. Plenty of hot gas remains available but does not cool and condense into star-forming clouds. Active galactic nuclei (AGNs) release enough energy to inhibit cooling of the hot gas, but energetic arguments alone do not explain why quenching of star formation is most effective in high-mass galaxies. In fact, optical observations show that quenching is more closely related to a galaxy’s central stellar velocity dispersion (σ v ) than to any other characteristic. Here we show that high σ v is critical to quenching because a deep central potential well maximizes the efficacy of AGN feedback. In order to remain quenched, a galaxy must continually sweep out the gas ejected from its aging stars. Supernova heating can accomplish this task as long as the AGN sufficiently reduces the gas pressure of the surrounding circumgalactic medium (CGM). We find that CGM pressure acts as the control knob on a valve that regulates AGN feedback and suggest that feedback power self-adjusts so that it suffices to lift the CGM out of the galaxy’s potential well. Supernova heating then drives a galactic outflow that remains homogeneous if . The AGN feedback can effectively quench galaxies with a comparable velocity dispersion, but feedback in galaxies with a much lower velocity dispersion tends to result in convective circulation and accumulation of multiphase gas within the galaxy.

Lessons on Star-forming Ultra-diffuse Galaxies from the Stacked Spectra of the Sloan Digital Sky Survey

Abstract We investigate the on-average properties for 28 star-forming ultra-diffuse galaxies (UDGs) located in low-density environments, by stacking their spectra from the Sloan Digital Sky Survey. These relatively isolated UDGs, with stellar masses of , have the on-average total stellar metallicity [M/H] ∼ −0.82 ± 0.14, iron metallicity [Fe/H] ∼ −1.00 ± 0.16, stellar age t * ∼ 5.2 ± 0.5 Gyr, α-enhancement [α/Fe] ∼ 0.24 ± 0.10, and oxygen abundance 12+log(O/H) ∼ 8.16 ± 0.06, as well as central stellar velocity dispersion 54 ± 12 km s−1. On the star formation rate versus stellar mass diagram, these UDGs are located lower than the extrapolated star-forming main sequence from the massive spirals, but roughly follow the main sequence of low-surface-brightness dwarf galaxies. We find that these star-forming UDGs are not particularly metal-poor or metal-rich for their stellar masses, as compared with the metallicity–mass relations of the nearby typical dwarfs. With the UDG data of this work and previous studies, we also find a coarse correlation between [Fe/H] and magnesium-element enhancement [Mg/Fe] for UDGs: [Mg/Fe] ≃ −0.43(±0.26) [Fe/H] −0.14(±0.40).

Velocity Dispersions of Brightest Cluster Galaxies and Their Host Clusters

Abstract We explore connections between brightest cluster galaxies (BCGs) and their host clusters. We first construct a HeCS-omnibus cluster sample including 227 galaxy clusters within 0.02 &lt; z &lt; 0.30; the total number of spectroscopic members from MMT/Hectospec and SDSS observations is 52325. Taking advantage of the large spectroscopic sample, we compute physical properties of the clusters including the dynamical mass and cluster velocity dispersion (σ cl). We also measure the central stellar velocity dispersion of the BCGs ( ) to examine the relation between BCG velocity dispersion and cluster velocity dispersion for the first time. The observed relation between BCG velocity dispersion and the cluster velocity dispersion is remarkably tight. Interestingly, the ratio decreases as a function of σ cl unlike the prediction from the numerical simulation of Dolag et al. The trend in suggests that BCG formation is more efficient in lower mass halos.

Stellar Kinematics and Environment at z ∼ 0.8 in the LEGA-C Survey: Massive Slow Rotators Are Built First in Overdense Environments

Abstract In this Letter, we investigate the impact of environment on integrated and spatially resolved stellar kinematics of a sample of massive, quiescent galaxies at intermediate redshift (0.6 &lt; z &lt; 1.0). For this analysis, we combine photometric and spectroscopic parameters from the UltraVISTA and Large Early Galaxy Astrophysics Census surveys in the COSMOS field and environmental measurements. We analyze the trends with overdensity (1+δ) on the rotational support of quiescent galaxies and find no universal trends at either fixed mass or fixed stellar velocity dispersion. This is consistent with previous studies of the local universe; rotational support of massive galaxies depends primarily on stellar mass. We highlight two populations of massive galaxies ( ) that deviate from the average mass relation. First, the most massive galaxies in the most underdense regions ((1 + δ) ≤ 1) exhibit elevated rotational support. Similarly, at the highest masses ( ) the range in rotational support is significant in all but the densest regions. This corresponds to an increasing slow-rotator fraction such that only galaxies in the densest environments ((1 + δ) ≥ 3.5) are primarily (90% ± 10%) slow rotators. This effect is not seen at fixed velocity dispersion, suggesting minor merging as the driving mechanism: only in the densest regions have the most massive galaxies experienced significant minor merging, building stellar mass and diminishing rotation without significantly affecting the central stellar velocity dispersion. In the local universe, most massive galaxies are slow rotators, regardless of environment, suggesting minor merging occurs at later cosmic times (z ≲ 0.6) in all but the most dense environments.

Stellar population properties of ETGs in compact groups of galaxies

ABSTRACT We present results on the study of the stellar population in early-type galaxies (ETGs) belonging to 151 compact groups (CGs). We also selected a field sample composed of 846 ETGs to investigate environmental effects on galaxy evolution. We find that the dependences of mean stellar ages, [Z/H] and [α/Fe] on central stellar velocity dispersion are similar, regardless where the ETG resides, CGs or field. When compared to the sample of centrals and satellites from the literature, we find that ETGs in CGs behave similarly to centrals, especially those embedded in low-mass haloes ($M_{\mathrm{ h}} \lt 10^ {12.5}\, \mathrm{M}_{\odot }$). Except for the low-mass limit, where field galaxies present a star-forming signature, not seen in CGs, the ionization agent of the gas in CG and field galaxies seem to be similar due to hot, evolved low-mass stars. However, field ETGs present an excess of H α emission relative to ETGs in CGs. Additionally, we performed a dynamical analysis, which shows that CGs present a bimodality in the group velocity dispersion distribution – a high- and low-σ mode. Our results indicate that high-σ groups have a smaller fraction of spirals, shorter crossing times, and a more luminous population of galaxies than the low-σ groups. It is important to emphasize that our findings point to a small environmental impact on galaxies located in CGs. The only evidence we find is the change in gas content, suggesting environmentally driven gas loss.