We analyse the spatially-resolved stellar populations of 9 local ($z<0.1$) Brightest Cluster Galaxies (BCGs) observed with VIMOS in IFU mode. Our sample is composed of 7 slow-rotating and 2 fast-rotating BCGs. We do not find a connection between stellar kinematics and stellar populations in this small sample. The BCGs have shallow metallicity gradients (median $Δ$[Fe/H] $= -0.11\pm0.1$), high central metallicities (median $[$Fe/H]$_{[α/Fe]=0} = 0.13\pm0.07$), and a wide range of central ages (from 5 to 15 Gyr). We propose that the reason for this is diverse evolutionary paths in BCGs. 67 per cent of the sample (6/9) show $\sim 7$ Gyr old central ages, which reflects an active accretion history, and 33 per cent of the sample (3/9) have central ages older than 11 Gyr, which suggest no star formation since $z=2$. The BCGs show similar central stellar populations and stellar population gradients to early-type galaxies of similar mass (M$_{dyn}> 10^{11.3}$M$_{\odot}$) from the ATLAS$^{3D}$ survey (median [Z/H] $= 0.04\pm0.07$, $Δ$[Z/H] $= -0.19\pm0.1$). However, massive early-type galaxies from ATLAS$^{3D}$ have consistently old ages (median Age $=12.0\pm3.8$Gyr). We also analyse the close massive companion galaxies of two of the BCGs. These galaxies have similar stellar populations to their respective BCGs.
Using Multi-Unit Spectroscopic Explorer (MUSE) spectroscopy, we analyse the stellar kinematics of 18 brightest group early-type (BGEs) galaxies, selected from the Complete Local-Volume Groups Sample (CLoGS). We analyse the kinematic maps for distinct features, and measure specific stellar angular momentum within one effective radius ($λ_{e}$). We classify the BGEs as fast (10/18) or slow (8/18) rotators, suggesting at least two different evolution paths. We quantify the anti-correlation between higher-order kinematic moment $h_{3}$ and V/$σ$ (using the $ξ_{3}$ parameter), and the kinematic mis…
Long dynamical timescales in the outskirts of galaxies preserve the information content of their accretion histories, for example in the form of stellar population gradients. We present a detailed analysis of the stellar halo properties of a statistically representative sample of early-type galaxies from the Illustris simulation and show that stellar population gradients at large radii can indeed be used to infer basic properties of galactic accretion histories. We measure metallicity, age, and surface-brightness profiles in quiescent Illustris galaxies ranging from $\mathrm{M}_\star = 10^{10}…
We apply our recently proposed "quadratic genetic modification" approach to generating and testing the effects of alternative mass accretion histories for a single $Λ$CDM halo. The goal of the technique is to construct different formation histories, varying the overall contribution of mergers to the fixed final mass. This enables targeted studies of galaxy and dark matter halo formation's sensitivity to the smoothness of mass accretion. Here, we focus on two dark matter haloes, each with four different mass accretion histories. We find that the concentration of both haloes systematically decre…
According to the current galaxy formation paradigm, mergers and interactions play an important role in shaping present-day galaxies. The remnants of this merger activity can be used to constrain galaxy formation models. In this work we use a sample of thirty hydrodynamical simulations of Milky Way-mass halos, from the AURIGA project, to generate surface brightness maps and search for the brightest stream in each halo as a function of varying limiting magnitude. We find that none of the models shows signatures of stellar streams at $μ_{r}^{lim} \leq 25$ mag arcsec$^{-2}$. The stream detection i…
It is generally recognized that massive galaxies form through a combination of in-situ collapse and ex-situ accretion. The in-situ component forms early, where gas collapse and compaction leads to the formation of massive compact systems (blue and red "nuggets") seen at $z>1$. The subsequent accretion of satellites brings in ex-situ material, growing these nuggets in size and mass to appear as the massive early-type galaxies (ETGs) we see locally. Due to stochasticity in the accretion process, in a few rare cases a red nugget will evolve to the present day having undergone little ex-situ mass …
I use a library of controlled minor merger N-body simulations, a particle tagging technique and Monte Carlo generated $Λ$CDM accretion histories to study the highly stochastic process of stellar deposition onto the accreted stellar halos (ASHs) of $L_*$ galaxies. I explore the main physical mechanisms that drive the connection between the accretion history and the density profile of the ASH. I find that: i) through dynamical friction, more massive satellites are more effective at delivering their stars deeper into the host; ii) as a consequence, ASHs feature a negative gradient between radius …
(Abridged) We propose a new method to estimate the Bondi (hot gas) accretion rates, \dot M_B, onto the supermassive black holes (SMBHs) at the centres of elliptical galaxies. It can be applied even if the Bondi radius is not well-resolved in X-ray observations. This method is based on two simple assumptions: (1) hot gas outside the Bondi radius is in nearly a hydrostatic equilibrium, and (2) the gas temperature near the galaxy centre is close to the virial temperature. We apply this method to 28 bright elliptical galaxies in nearby galaxy clusters (27 of them are the brightest cluster galaxies…
In the era of large-scale spectroscopic surveys in the Local Group (LG), we can explore using chemical abundances of halo stars to study the star formation and chemical enrichment histories of the dwarf galaxy progenitors of the Milky Way (MW) and M31 stellar halos. In this paper, we investigate using the Chemical Abundance Ratio Distributions (CARDs) of seven stellar halos from the Latte suite of FIRE-2 simulations. We attempt to infer galaxies' assembly histories by modelling the CARDs of the stellar halos of the Latte galaxies as a linear combination of template CARDs from disrupted dwarfs,…
To advance our understanding of the fuelling and feedback processes which power the Universe's most massive black holes, we require a significant increase in our knowledge of the molecular gas which exists in their immediate surroundings. However, the behaviour of this gas is poorly understood due to the difficulties associated with observing it directly. We report on a survey of 18 brightest cluster galaxies lying in cool cores, from which we detect molecular gas in the core regions of eight via carbon monoxide (CO), cyanide (CN) and silicon monoxide (SiO) absorption lines. These absorption l…
Irregular dwarf galaxies of the Local Group have very varied properties and star formation histories. Some of them formed the majority of their stars very late compared to the others. Extreme examples are Leo A and Aquarius which reached the peak of star formation at $z<1$ ( > 6 Gyr after BB). This fact seemingly challenges the LCDM cosmology because the dark matter halos of these galaxies on average should assemble the majority of their masses before z~2 (<3 Gyr after BB). In this work we investigate whether the delayed star formation histories of some irregular dwarf galaxies could be explai…
Explaining the internal distribution and motions of stars and gas in galaxies is a key aspect in understanding their evolution. In previous work we identified five well resolved galaxies with atypical kinematics from a cosmological simulation; two had kinematically distinct cores (KDCs), and three had counter-rotating gas and stars (CRGD). In this paper, we show that i) the KDC galaxies have flattening of stellar [O/Fe] at large galacto-centric radii due to the minor mergers that gave rise to the KDCs, and ii) the CRGD galaxies have an abrupt transition in the gas metallicity maps, from high m…
We present the results of a survey of the brightest UV-selected galaxies in protoclusters. These proto-brightest cluster galaxy (proto-BCG) candidates are drawn from 179 overdense regions of $g$-dropout galaxies at $z\sim4$ from the Hyper Suprime-Cam Subaru Strategic Program identified previously as good protocluster candidates. This study is the first to extend the systematic study of the progenitors of BCGs from $z\sim2$ to $z\sim4$. We carefully remove possible contaminants from foreground galaxies and, for each structure, we select the brightest galaxy that is at least 1 mag brighter than …
We measure the role of major and minor mergers in forming the stellar masses of galaxies over $0<z<3$ using a combination of $\sim 3.25$ deg$^{2}$ of the deepest ground based near-infrared imaging taken to date as part of the REFINE survey. We measure the pair fraction and merger fractions for galaxy mergers of different mass ratios, and quantify the merger rate with newly measured time-scales derived from the Illustris simulation as a function of redshift and merger mass ratio. We find that over $0 < z < 3$ major mergers with mass ratios greater than 1:4 occur $0.85^{+0.19}_{-0.20}$ times on …
A fraction of brightest cluster galaxies (BCGs) shows bright emission in the UV and the blue part of the optical spectrum, which has been interpreted as evidence of recent star formation. Most of these results are based on the analysis of broadband photometric data. Here, we study the optical spectra of a sample of 19 BCGs hosted by X-ray luminous galaxy clusters at 0.15 < z < 0.3, a subset from the Canadian Cluster Comparison Project (CCCP) sample. We identify plausible star formation histories of the galaxies by fitting Simple Stellar Populations (SSPs) as well as composite populations, cons…
There is increasing observational and theoretical evidence for a correlation between the metallicity and the mass of the stellar halo for galaxies with Milky Way-like stellar masses. Using the Illustris cosmological hydrodynamical simulations, we find that this relationship arises because a single massive massive progenitor contributes the bulk of the mass to the accreted stellar component as well as sets its metallicity. Moreover, in the Illustris simulations, this relationship extends over 3 orders of magnitude in accreted stellar mass for central galaxies. We show that for Milky Way-like ma…
Active galactic nuclei play a crucial role in the accretion and ejection of gas in galaxies. Although their outflows are well studied, finding direct evidence of accretion has proved very difficult and has so far been done for very few sources. A promising way to study the significance of cold accretion is by observing the absorption of an active galactic nucleus's extremely bright radio emission by the cold gas lying along the line-of-sight. As such, we present ALMA CO(1-0) and CO(2-1) observations of the Hydra-A brightest cluster galaxy (z=0.054) which reveal the existence of cold, molecular…
X-ray and microwave cluster scaling relations are immensely valuable for cosmological analysis. However, their power is limited by astrophysical systematics that bias mass estimates and introduce additional scatter. Turbulence injected into the intracluster medium via mass assembly contributes substantially to cluster non-thermal pressure support, a significant source of such uncertainties. We use an analytical model to compute the assembly-driven non-thermal pressure profiles of haloes based on Monte Carlo-generated accretion histories. We introduce a fitting function for the average non-ther…
We present constraints on the timescale of star formation variability and the correlation between star formation and host halo accretion histories of star-forming (SF) central galaxies from the scatter of the stellar-to-halo mass relation (SHMR). SF galaxies are found to have a tight relationship between their star formation rates and stellar masses on the so-called "star-forming sequence" (SFS), which characterizes their SF histories and $M_*$ growths. Meanwhile, observed SHMR constraints connect $M_*$ growth to halo accretion history. Combining these observed trends with a cosmological $N$-b…
On dwarf galaxy scales, the different shapes of the galaxy stellar mass function and the dark halo mass function require a star-formation efficiency (SFE) in these systems that is currently more than 1 dex lower than that of Milky Way-size halos. Here, we argue that this trend may actually be reversed at high redshift. Specifically, by combining the resolved star-formation histories of nearby isolated dwarfs with the simulated mass-growth rates of dark matter halos, we show that the assembly of these systems occurs in two phases: (1) an early, fast halo accretion phase with a rapidly deepening…
We study the dependence of the properties of group galaxies on the surrounding large-scale environment, using SDSS-DR7 data. Galaxies are ranked according to their luminosity within each group and classified morphologically by the Sérsic index. We have considered samples of the host groups in superstructures of galaxies, and elsewhere. We find a significant dependence of the properties of late-type brightest group galaxies on the large-scale environment: they show statistically significant higher luminosities and stellar masses, redder u-r colours, lower star formation activity and longer star…
Active galactic nucleus activity in brightest cluster galaxies at intermediate redshifts in Sunyaev-Zel'dovich--selected clusters
South African Astronomical Observatory（南非天文台）；Department of Astronomy, University of Cape Town（开普敦大学天文学系）；Wits Centre for Astrophysics, School of Physics, University of the Witwatersrand（威特沃特斯兰德大学物理学院天体物理中心）；School of Mathematics, Statistics & Computer Science, University of KwaZulu-Natal（夸祖鲁-纳塔尔大学数学、统计与计算机科学学院）；Centre for Space Research, North-West University（西北大学空间研究中心）；National Institute for Theoretical and Computational Sciences (NITheCS)（国家理论与计算科学研究所）；Inter-University Centre for Astronomy and Astrophysics（大学间天文学与天体物理学中心）
We use very high-S/N stacked spectra of $\sim$29,000 nearby quiescent early-type galaxies (ETGs) from the Sloan Digital Sky Survey (SDSS) to investigate variations in their star formation histories (SFHs) with environment at fixed position along and perpendicular to the Fundamental Plane (FP). We define three classifications of local group environment based on the `identities' of galaxies within their dark matter halos: central `Brightest Group Galaxies' (BGGs); Satellites; and Isolateds (those `most massive' in a dark matter halo with no Satellites). We find that the SFHs of quiescent ETGs ar…
We analyze a suite of 33 cosmological simulations of the evolution of Milky Way-mass galaxies in low-density environments. Our sample spans a broad range of Hubble types at z=0, from nearly bulgeless disks to bulge-dominated galaxies. Despite the fact that a large fraction of the bulge is typically in place by z=1, we find no significant correlation between the morphology at z=1 and at z=0. The z=1 progenitors of disk galaxies span a range of morphologies, including smooth disks, unstable disks, interacting galaxies and bulge-dominated systems. By z=0.5, spiral arms and bars are largely in pla…
We combine IR, optical and X-ray data from the overlapping, 9.3 square degree NOAO Deep Wide-Field Survey (NDWFS), AGN and Galaxy Evolution Survey (AGES), and XBootes Survey to measure the X-ray evolution of 6146 normal galaxies as a function of absolute optical luminosity, redshift, and spectral type over the largely unexplored redshift range 0.1 < z < 0.5. Because only the closest or brightest of the galaxies are individually detected in X-rays, we use a stacking analysis to determine the mean properties of the sample. Our results suggest that X-ray emission from spectroscopically late-type …
We present new deep photometry of the rich globular cluster (GC) systems around the Brightest Cluster Galaxies UGC 9799 (Abell 2052) and UGC 10143 (Abell 2147), obtained with the HST ACS and WFC3 cameras. For comparison, we also present new reductions of similar HST/ACS data for the Coma supergiants NGC 4874 and 4889. All four of these galaxies have huge cluster populations (to the radial limits of our data, comprising from 12000 to 23000 clusters per galaxy). The metallicity distribution functions (MDFs) of the GCs can still be matched by a bimodal-Gaussian form where the metal-rich and metal…
Early-type (E and S0) galaxies may have assembled via a variety of different evolutionary pathways. Here we investigate these pathways by comparing the stellar kinematic properties of 24 early-type galaxies from the SLUGGS survey with the hydrodynamical simulations of Naab et al. (2014). In particular, we use the kinematics of starlight up to 4 effective radii (R$_e$) as diagnostics of galaxy inner and outer regions, and assign each galaxy to one of six Naab et al. assembly classes. The majority of our galaxies (14/24) have kinematic characteristics that indicate an assembly history dominated …
Using a sample of 425 nearby Brightest Cluster Galaxies (BCGs) from von der Linden et al. (2007), we study the relationship between their internal properties (stellar masses, structural parameters and morphologies) and their environment. More massive BCGs tend to inhabit denser regions and more massive clusters than lower mass BCGs. Furthermore, cDs, which are BCGs with particularly extended envelopes, seem to prefer marginally denser regions and tend to be hosted by more massive halos than elliptical BCGs. cD and elliptical BCGs show parallel positive correlations between their stellar masses…
BAQARO: Tracing Stochastic Black Hole Growth Histories and Quasar Lightcurves in a Cosmological Context
Center for Astrophysics | Harvard & Smithsonian（天体物理中心 | 哈佛与史密森尼学会）；Leiden Observatory, Leiden University（莱顿天文台，莱顿大学）；Department of Physics, University of California, Santa Barbara（加州大学圣塔芭芭拉分校物理系）
Observations of 170 local ($z\lesssim0.08$) galaxy clusters in the northern hemisphere have been obtained with the Wendelstein Telescope Wide Field Imager (WWFI). We correct for systematic effects such as point-spread function broadening, foreground star contamination, relative bias offsets, and charge persistence. Background inhomogeneities induced by scattered light are reduced down to $Δ{\rm SB} > 31~g'$ mag arcsec$^{-2}$ by large dithering and subtraction of night-sky flats. Residual background inhomogeneities brighter than ${\rm SB}_σ< 27.6~g'$ mag arcsec$^{-2}$ caused by galactic cirrus …
Observational systematics complicate comparisons with theoretical models limiting understanding of galaxy evolution. In particular, different empirical determinations of the stellar mass function imply distinct mappings between the galaxy and halo masses, leading to diverse galaxy evolutionary tracks. Using our state-of-the-art STatistical sEmi-Empirical modeL, STEEL, we show fully self-consistent models capable of generating galaxy growth histories that simultaneously and closely agree with the latest data on satellite richness and star-formation rates at multiple redshifts and environments. …
Co-evolution of Supermassive Black Holes and their Host L* galaxies: implications for Milky Way and M31
Universidad de Buenos Aires, Facultad de Ciencias Exactas y Naturales（布宜诺斯艾利斯大学，理学院）；CONICET-Universidad de Buenos Aires, Instituto de Astronomía y Física del Espacio (IAFE)（阿根廷国家科学研究委员会-布宜诺斯艾利斯大学，天体物理学与空间物理研究所（IAFE））；Astrophysics Research Institute, Liverpool John Moores University（利物浦约翰摩尔斯大学，天体物理研究所）
Satellites constitute an important fraction of the overall galaxy population and are believed to form in dark matter subhalos. Here we use the cosmological hydrodynamic simulation TNG100 to investigate how the formation histories of subhalos affect the properties and evolution of their host galaxies. We use a scaled formation time ($a_{\rm nf}$) to characterize the mass assembly histories of the subhalos before they are accreted by massive host halos. We find that satellite galaxies in young subhalos (low $a_{\rm nf}$) are less massive and more gas rich, and have stronger star formation and a …
The most evident features of colour-magnitude diagrams of galaxies are the red sequence of quiescent galaxies, extending up to the brightest elliptical galaxies, and the blue cloud of star-forming galaxies, which is truncated at a luminosity L~L*. The truncation of the blue cloud indicates that in the most massive systems star formation must be quenched. For this to happen the virial-temperature galactic gas must be kept hot and any accreted cold gas must be heated. The elimination of accreted cold gas can be due to thermal evaporation by the hot interstellar medium, which in turn is prevented…
Using a new, high-resolution cosmological hydrodynamic simulation of a Milky Way-type (MW-type) galaxy, we explore how a merger-rich assembly history affects the mass budget of the central supermassive black hole (SMBH). We examine a MW-mass halo at the present epoch whose evolution is characterized by several major mergers to isolate the importance of merger history on black hole accretion. This study is an extension of Bellovary et. al. 2013, which analyzed the accretion of high mass, high redshift galaxies and their central black holes, and found that the gas content of the central black ho…
In the context of large scale structure formation, clusters of galaxies are located at the nodes of the cosmic web, and continue to accrete galaxies and groups along filaments. They show sometimes a very large extension and a preferential direction. Brightest cluster galaxies (BCGs) are believed to grow through the accretion of many small galaxies, and their structural properties are expected to vary with redshift. In some cases BCGs show an orientation comparable to that of the cluster to which they belong. We analyse the morphological properties of 38 BCGs from the DAFT/FADA and CLASH survey…
We report the discovery of significant localized structures in the projected two-dimensional (2D) spatial distributions of the Globular Cluster (GC) systems of the ten brightest galaxies in the Virgo Cluster. We use catalogs of GCs extracted from the HST ACS Virgo Cluster Survey (ACSVCS) imaging data, complemented, when available, by additional archival ACS data. These structures have projected sizes ranging from $\sim\!5$ arcsec to few arc-minutes ($\sim\!1$ to $\sim\!25$ kpc). Their morphologies range from localized, circular, to coherent, complex shapes resembling arcs and streams. The larg…
Variability of a galaxy's core radio source can be a significant consequence of AGN accretion. However, this variability has not been well studied, particularly at high radio frequencies. As such, we report on a campaign monitoring the high radio frequency variability of 20 nearby, cool-core brightest cluster galaxies. From our representative sample, we show that most vary significantly over timescales of approximately one year and longer. Our highest cadence observations are at 15 GHz and are from the Owens Valley Radio Observatory (OVRO). They have a median time interval of 7 days and mostly…
We examine the radio properties of the Brightest Cluster Galaxies (BCGs) in a large sample of X-ray selected galaxy clusters comprising the Brightest Cluster Sample (BCS), the extended BCS (eBCS) and ROSAT-ESO Flux Limited X-ray (REFLEX) cluster catalogues. We have multi-frequency radio observations of the BCG using a variety of data from the Australia Telescope Compact Array (ATCA), Jansky Very Large Array (VLA) and Very Long Baseline Array (VLBA) telescopes. The radio spectral energy distributions (SEDs) of these objects are decomposed into a component attributed to on-going accretion by the…
We use Chandra X-ray observations to look for evidence of a recoiling black hole from the brightest cluster galaxy in Abell 2261 (A2261-BCG). A2261-BCG is a strong candidate for a recoiling black hole because of its large, flat stellar core, revealed by Hubble Space Telescope imaging observations. We took 100-ksec observations with Chandra and combined it with 35 ksec of archival observations to look for low-level accretion onto a black hole of expected mass $M\sim10^{10}\ M_{\scriptscriptstyle \odot}$ that could possibly be located in one of four off-center stellar knots near the galaxy's cen…
IRAC data have long implied that early ($z\gtrsim6$) galaxies often have very high specific star formation rates (sSFR$\gtrsim$30 Gyr$^{-1}$), but JWST data have shown that at least some early galaxies are forming stars far less vigorously. Here, we systematically analyze the recent star formation histories (SFHs) of a large ($N=368$) sample of $z\sim6$ Lyman-break galaxies (LBGs) spanning $-22\lesssim M_\mathrm{UV}\lesssim-16$ assembled from ACS+NIRCam imaging in the GOODS and Abell 2744 fields. We find that very low H$α$-to-UV luminosity ratios ($L_\mathrm{Hα}/L_\mathrm{UV}$) and strong rece…
There have been several recent claims of black hole binaries in globular clusters. I show that these candidate systems could instead be ultracompact X-ray binaries (UCXBs) in which a neutron star accretes from a white dwarf. They would represent a slightly earlier evolutionary stage of known globular cluster UCXBs such as 4U 1820--30, with white dwarf masses $\sim 0.2\msun$, and orbital periods below 5 minutes. Accretion is slightly super--Eddington, and makes these systems ultraluminous sources (ULXs) with rather mild beaming factors $b \sim 0.3$. Their theoretical luminosity function flatten…
We use high-resolution, multi-band imaging of ~16,500 galaxies in the CANDELS fields at 0 < z < 2.5 to study the evolution of color gradients and half-mass radii over cosmic time. We find that galaxy color gradients at fixed mass evolve rapidly between z~2.5 and z~1, but remain roughly constant below z~1. This result implies that the sizes of both star-forming and quiescent galaxies increase much more slowly than previous studies found using half-light radii. The half-mass radius evolution of quiescent galaxies is fully consistent with a model which uses observed minor merger rates to predict …
New deep optical and near-infrared imaging is combined with archival ultraviolet and infrared data for fifteen nearby galaxies mapped in the Spitzer Extended Disk Galaxy Exploration Science survey. These images are particularly deep and thus excellent for studying the low surface brightness outskirts of these disk-dominated galaxies with stellar masses ranging between 10^8 and 10^11 Msun. The spectral energy distributions derived from this dataset are modeled to investigate the radial variations in the galaxy colors and star formation histories. Taken as a whole, the sample shows bluer and you…
We present high-resolution (synthesised beam size 0."088x0."083 or 25x23 pc$^2$) Atacama Large Millimetre/submillimetre Array (ALMA) $^{12}$CO(2-1) line and 236 GHz continuum observations, as well as 5 GHz enhanced Multi-Element Radio Linked Interferometer Network (e-MERLIN) continuum observations, of NGC 0708; the brightest galaxy in the low-mass galaxy cluster Abell 262. The line observations reveal a turbulent, rotating disc of molecular gas in the core of the galaxy, and a high-velocity, blue-shifted feature ~0."4 (~113 pc) from its centre. The sub-millimetre continuum emission peaks at th…
We present eight monitoring seasons of the four brightest images of the gravitational lens SDSS J1004+4112 observed between December 2003 and October 2010. Using measured time delays for the images A, B and C and the model predicted time delay for image D we have removed the intrinsic quasar variability, finding microlensing events of about 0.5 and 0.7 mag of amplitude in the images C and D. From the statistics of microlensing amplitudes in images A, C, and D, we have inferred the half-light radius (at λ rest = 2407 Å) for the accretion disk using two different methods, $R_{1/2}=8.7^{+18.5}_{-…
We study the radio emission of the most massive galaxies in a sample of dynamically relaxed and un-relaxed galaxy groups from Galaxy and Mass Assembly (GAMA). The dynamical state of the group is defined by the stellar dominance of the brightest group galaxy, e.g. the luminosity gap between the two most luminous members, and the offset between the position of the brightest group galaxy and the luminosity centroid of the group. We find that the radio luminosity of the most massive galaxy in the group strongly depends on its environment, such that the brightest group galaxies in dynamically young…
