Rich Clusters Of Galaxies Research Articles

The COld STream finder Algorithm (COSTA)

Context. We present the COld STream finder Algorithm (COSTA), a novel algorithm used to search for cold kinematical substructures in the phase space of planetary nebulae (PNe) and globular clusters (GCs) in the halos of massive galaxies and intracluster regions. Aims. The aim of COSTA is to detect small, low-velocity-dispersion streams, such as the ones produced in recent interactions of dwarf galaxies with the halos of more massive galaxies, including the ones sitting in the central regions of rich galaxy clusters. Methods. We based COSTA on a deep friend-of-friend procedure that isolates groups of N particles with low velocity dispersion (between 10 km s−1 and ∼100 km s−1) using an iterative (n) sigma-clipping on a defined number of (k) neighbor particles. The algorithm has three parameters (k − n − N), plus a velocity dispersion cut-off that defines the “coldness” of the stream, which are set using Monte Carlo realizations of the sample in question. Results. In this paper, we show the ability of COSTA to recover simulated streams on mock datasets of discrete kinematical tracers of different sizes and measurement errors, from publicly available hydrodynamical simulations. We also show the best algorithm setup for realistically locating streams in the core of the Fornax cluster, for future applications of COSTA to real populations of PNe and GCs. Conclusions. Finally, COSTA can be adapted to many situations in finding small substructures in the phase space of a limited sample of discrete tracers, provided that the algorithm is trained on realistic mock observations reproducing the specific dataset under examination.

The results of analysis of Rich Galaxy Clusters from CfA2 Redshift Survey spatial distribution

Preliminary results of the investigation of the properties of 7 galaxy cluster from CfA2 redshift survey are discussed in the presented article. Clusters 933, 142, 1046, and 1652 have several peculiarities of the spatial distributions of galaxies. The distributions on absolute magnitude and luminosity represent two areas for clusters 933, 88, 142, 1046, 1101. The investigation of the spatial distribution and other characteristics of 88, 1101, 1046, 142, 933, 1242 and 1652 galaxy clusters allow concluding gravitational lensing effect. Galaxies from these areas are paired accordingly its spectral characteristics and position. Redshifts of these clusters are in the region 0.002 – 0.022. Preliminary results of analysis allow us concluding compact objects or dark matter blobs as lenses. Moreover, groups #933, #142, #1046 and #1652 reveals high-energy γ-associations on Fermi/LAT 10-Year Point Source Catalog 4FGL-DR2 (4FGL J1144.9 + 1937, 4FGL J0152.2 + 3714, 4FGL J1230.8 + 1223 and 4FGL J1653.8 + 3945); and sources 4FGL J0123.1+3421, 4FGL J1259.5+2332, 4FGL J1353.2+3740 are located inside sizes of clusters #88, #1101 and #1242. Also several anomalies of spatial dynamic of galaxies in these clusters were separated. Joint observations of such clusters by orbital gamma-ray observatories with high angular resolution and ground-based Cherenkov air-shower experiments could possibly clarify the type of gravitational lensing and processes of particle acceleration in these objects especially highest energy of emitted gammas. Thus we propose including these and similar clusters in the programs of observations of the planned experiment GAMMA-400 (Gamma Astronomical Multifunctional Modular Apparatus) with angular resolution ~0.01° at Eγ = 100 GeV. Also now it is discussed coordination of multiwavelength observations program of Cherenkov Telescope Array (CTA) and GAMMA-400 objects list for observations. Moreover, common observations of such clusters by orbital gamma-ray telescopes with high angular resolution and ground-based Cherenkov air-shower experiments could possibly clarify the type of gravitational lenses.

Radio Galaxy Zoo: new giant radio galaxies in the RGZ DR1 catalogue

ABSTRACT In this paper, we present the identification of five previously unknown giant radio galaxies (GRGs) using Data Release 1 of the Radio Galaxy Zoo citizen science project and a selection method appropriate to the training and validation of deep learning algorithms for new radio surveys. We associate one of these new GRGs with the brightest cluster galaxy (BCG) in the galaxy cluster GMBCG J251.67741+36.45295 and use literature data to identify a further 13 previously known GRGs as BCG candidates, increasing the number of known BCG GRGs by $\gt 60$ per cent. By examining local galaxy number densities for the number of all known BCG GRGs, we suggest that the existence of this growing number implies that GRGs are able to reside in the centres of rich (∼1014 M⊙) galaxy clusters and challenges the hypothesis that GRGs grow to such sizes only in locally underdense environments.

Active gas features in three HSC-SSP CAMIRA clusters revealed by high angular resolution analysis of MUSTANG-2 SZE and XXL X-ray observations

ABSTRACT We present results from simultaneous modelling of high angular resolution GBT/MUSTANG-2 90 GHz Sunyaev–Zel’dovich effect (SZE) measurements and XMM-XXL X-ray images of three rich galaxy clusters selected from the HSC-SSP Survey. The combination of high angular resolution SZE and X-ray imaging enables a spatially resolved multicomponent analysis, which is crucial to understand complex distributions of cluster gas properties. The targeted clusters have similar optical richnesses and redshifts, but exhibit different dynamical states in their member galaxy distributions: a single-peaked cluster, a double-peaked cluster, and a cluster belonging to a supercluster. A large-scale residual pattern in both regular Compton-parameter y and X-ray surface brightness distributions is found in the single-peaked cluster, indicating a sloshing mode. The double-peaked cluster shows an X-ray remnant cool core between two SZE peaks associated with galaxy concentrations. The temperatures of the two peaks reach ∼20–30 keV in contrast to the cool core component of ∼2 keV, indicating a violent merger. The main SZE signal for the supercluster is elongated along a direction perpendicular to the major axis of the X-ray core, suggesting a minor merger before core passage. The SX and y distributions are thus perturbed at some level, regardless of the optical properties. We find that the integrated Compton y parameter and the temperature for the major merger are boosted from those expected by the weak-lensing mass and those for the other two clusters show no significant deviations, which is consistent with predictions of numerical simulations.

Universal structure of dark matter haloes over a mass range of 20 orders of magnitude.

Cosmological models in which dark matter consists of cold elementary particles predict that the dark halo population should extend to masses many orders of magnitude below those at which galaxies can form1-3. Here we report a cosmological simulation of the formation of present-day haloes over the full range of observed halo masses (20 orders of magnitude) when dark matter is assumed to be in the form of weakly interacting massive particles of mass approximately 100gigaelectronvolts. The simulation has a full dynamic range of 30 orders of magnitude in mass and resolves the internal structure of hundreds of Earth-mass haloes in as much detail as it does for hundreds of rich galaxy clusters. We find that halo density profiles are universal over the entire mass range and are well described by simple two-parameter fitting formulae4,5. Halo mass and concentration are tightly related in a way that depends on cosmology and on the nature of the dark matter. For a fixed mass, the concentration is independent of the local environment for haloes less massive than those of typical galaxies. Haloes over the mass range of 10-3 to 1011 solar masses contribute about equally (per logarithmic interval) to the luminosity produced by dark matter annihilation, which we find to be smaller than all previous estimates by factors ranging up to one thousand3.

X-ray properties of high-richness CAMIRA clusters in the Hyper Suprime-Cam Subaru Strategic Program field

Abstract We present the first results of a pilot X-ray study of 37 rich galaxy clusters at 0.1 < z < 1.1 in the Hyper Suprime-Cam Subaru Strategic Program field. Diffuse X-ray emissions from these clusters were serendipitously detected in the XMM-Newton fields of view. We systematically analyze X-ray images of 37 clusters and emission spectra of a subsample of 17 clusters with high photon statistics by using the XMM-Newton archive data. The frequency distribution of the offset between the X-ray centroid or peak and the position of the brightest cluster galaxy was derived for the optical cluster sample. The fraction of relaxed clusters estimated from the X-ray peak offsets in 17 clusters is 29 ± 11(±13)%, which is smaller than that of the X-ray cluster samples such as HIFLUGCS. Since the optical cluster search is immune to the physical state of X-ray-emitting gas, it is likely to cover a larger range of the cluster morphology. We also derive the luminosity–temperature relation and found that the slope is marginally shallower than those of X-ray-selected samples and consistent with the self-similar model prediction of 2. Accordingly, our results show that the X-ray properties of the optical clusters are marginally different from those observed in the X-ray samples. The implication of the results and future prospects are briefly discussed.

Role of environment on AGN activity

AbstractMotivated by the apparently conflicting results reported in the literature on the effect of environment on nuclear activity, we have carried out a new analysis by comparing the fraction of galaxies hosting active galactic nuclei (AGNs) in the most overdense regions (rich galaxy clusters) and the most underdense ones (voids) in the local universe. Exploiting the classical BPT diagnostics, we have extracted volume limited samples of star forming and AGN galaxies. We find that, at variance with star-forming galaxies, AGN galaxies have similar distributions of specific star formation rates and of galactic ages (as indicated by the Dn4000 parameter) both in clusters and in voids. In both environments galaxies hosting AGNs are generally old, with low star formation activity. The AGN fraction increases faster with stellar mass in clusters than in voids, especially above 1010.2 M⊙. Our results indicate that, in the local universe, the nuclear activity correlates with stellar mass and galaxy morphology and is weakly, if at all, affected by the local galaxy density.

Role of Environment on Nuclear Activity

Abstract Motivated by the apparently conflicting results reported in the literature on the effect of environment on nuclear activity, we have carried out a new analysis by comparing the fraction of galaxies hosting active galactic nuclei (AGNs) in the most overdense regions (rich galaxy clusters) and the most underdense ones (voids) in the local universe. Exploiting the classical BPT diagnostics, we have extracted volume-limited samples of star-forming and AGN galaxies. We find that, at variance with star-forming galaxies, AGN galaxies have similar distributions of specific star formation rates and of galactic ages (as indicated by the D n 4000 parameter) both in clusters and in voids. In both environments galaxies hosting AGNs are generally old, with low star formation activity. The AGN fraction increases faster with stellar mass in clusters than in voids, especially above 1010.2 M ⊙. Our results indicate that, in the local universe, the nuclear activity correlates with stellar mass and galaxy morphology and is weakly, if at all, affected by the local galaxy density.

Investigation of the orientation of galaxies in clusters: the importance, methods and results of research

Various models of structure formation can account for various aspects of the galaxy formation process on different scales, as well as for various observational features of structures. Thus, the investigation of galaxies orientation constitute a standard test of galaxies formation scenarios since observed variations in angular momentum represent fundamental constraints for any model of galaxy formation. We have improved the method of analysis of the alignment of galaxies in clusters. Now, the method allows to analyze both position angles of galaxy major axes and two angles describing the spatial orientation of galaxies. The distributions of analyzed angles were tested for isotropy by applying different statistical tests. For sample of analyzed clusters we have computed the mean values of analyzed statistics, checking whether they are the same as expected ones in the case of random distribution of analyzed angles. The detailed discussion of this method has been performed. We have shown how to proceed in many particular cases in order to improve the statistical reasoning when analyzing the distribution of the angles in the observational data. Separately, we have compared these new results with those obtained from numerical simulations. We show how powerful is our method on the example of galaxy orientation analysis in 247 Abell rich galaxy clusters. We have found that the orientations of galaxies in analyzed clusters are not random. It means that we genuinely confirmed an existence of the alignment of galaxies in rich Abells' galaxy clusters. This result is independent from the clusters of Bautz-Morgan types.

High Confidence Optical Confirmations among the High Signal-to-noise Planck Cluster Candidates

Abstract We report on newly identified galaxy clusters from the high signal-to-noise (>5σ) end of the second all-sky Planck Sunyaev–Zel’dovich (SZ) catalog (PSZ2). The clusters are identified in deep, optical imaging from the Kitt Peak National Observatory 4 m Mayall telescope taken between 2014 and 2017. Here we focus on the highest richness systems, and identify galaxy clusters through a combination of the maxBCG algorithm and visual image inspection. Galaxy clusters are considered to be confirmed if they are both rich and spatially coincident (≲6′) with the reported PSZ2 position. Of the 85 fields containing unconfirmed PSZ2 candidates observed, we find 15 (17.6% of the observed sample) corresponding galaxy clusters (0.13 < z < 0.78), 12 of which are previously unrecognized as counterparts. To explain this low identification fraction, we consider three possible scenarios: that clusters are (1) mostly at low-z, (2) mostly at high-z, or (3) located in fields with high object density. None of these scenarios alone can account for the low purity of rich galaxy clusters among the high signal-to-noise PSZ2 unconfirmed candidates.

Regular Substructures in the Rich Open Galaxy Clusters

We present the results of study the 2D distribution of galaxies in 254 rich open galaxy clusters. The clusters have no concentration to the center, so all kinds of substructures are clearly seen. Regular linear substructures in galaxy clusters were described in Rood & Sastry scheme of morphological types according to positions of 10 brightest galaxies. Another types of regular substructures were missed. Our study fills the lacuna. We have found about 25% of clusters in our data set having four kinds of regular substructures, beyond founded before linear ones. New kinds of regular substructures are: crossing and divaricating filaments or X and Y-type peculiarities, as well as curved strips and short dense chains. We suppose the distribution of dark matter in founded galaxy clusters with substructures have corresponded regular peculiarities. Hot gas distribution in these clusters must be observed distorted X-ray halo. We suppose also the clusters will evolve in the different ways.

DETAILED MORPHOLOGY OF THE RICH CONCENTRATED GALAXY CLUSTERS

The results of the detailed analysis of the 2D distribution of galaxies in 28 rich galaxy clusters with significant concentration to the cluster center are present. The analysis was executed in these directions: the detection of regular substructures and peculiarities in the galaxy distribution. The role of brightest cluster members was taken into account too. The input data were selected from “The Catalogue of Galaxy Clusters and Groups” and list of galaxies of Muenster Red Sky Survey. Concentrated galaxy clusters are evolved, virialized structures. Substructures in this type of clusters must be feeblemarked. Nevertheless we detected ignificant part of concentrated galaxy clusters having different kinds of peculiarities, namely crossing and divaricating filaments or X and Y-type peculiarities, as well as curved strips and short dense chains. 2 clusters having extremely density of galaxies were attributed as superconcentrated/compact type.

Signatures of multiple episodes of AGN activity in the core of Abell 1795

In this paper we analyze AGN activity signatures in the rich nearby galaxy cluster Abell 1795 aiming to confirm and characterize the long-term feedback history in the system. We combine radio observations at 610 and 235 MHz from the Giant Metrewave Radio Telescope (GMRT) with 3.4 Msec X-ray data from the Chandra Observatory. Extracting radial temperature profiles, as well as X-ray and radio surface brightness profiles in three directions showing major morphological disturbances, we highlight the signatures of activity in the system. For the first time we observe radio emission corresponding to the NW X-ray depression, which provides evidence in favor of the classification of the depression as a cavity. We identify two other X-ray cavities situated NW and SW of the AGN. While the central radio emission corresponding to the inner cavities shows a flatter spectral index, the radio extensions associated with the farthest X-ray cavities consist of aged plasma. All observed signatures both in radio and X-ray are consistent with several consecutive episodes of AGN activity, which gave rise to the observed morphology NW and SW from the core. In the southern region, we confirm the cooling wake hypothesis for the origin of the long tail. The deep X-ray data also allows us to distinguish significant distortions in the tail’s inner parts, which we attribute to the activity of the AGN.

Ultra-red Galaxies Signpost Candidate Protoclusters at High Redshift

Abstract We present images obtained with LABOCA of a sample of 22 galaxies selected via their red Herschel SPIRE colors. We aim to see if these luminous, rare, and distant galaxies are signposting dense regions in the early universe. Our 870 μm survey covers an area of ≈1 deg2 down to an average rms of , with our five deepest maps going ≈2× deeper still. We catalog 86 dusty star-forming galaxies (DSFGs) around our “signposts,” detected above a significance of 3.5σ. This implies a overdensity of (or ) DSFGs, excluding our signposts, when comparing our number counts to those in “blank fields.” Thus, we are 99.93% confident that our signposts are pinpointing overdense regions in the universe, and ≈95% [50%] confident that these regions are overdense by a factor of at least ≥1.5 × [2×]. Using template spectral energy distributions (SEDs) and SPIRE/LABOCA photometry, we derive a median photometric redshift of z = 3.2 ± 0.2 for our signposts, with an inter-quartile range of z = 2.8–3.6, somewhat higher than expected for ∼850 μm selected galaxies. We constrain the DSFGs that are likely responsible for this overdensity to within of their respective signposts. These “associated” DSFGs are radially distributed within (physical) distances of 1.6 ± 0.5 Mpc from their signposts, have median star formation rates (SFRs) of (for a Salpeter stellar inital mass function) and median gas reservoirs of . These candidate protoclusters have average total SFRs of at least and space densities of ∼9 × 10−7 Mpc−3, consistent with the idea that their constituents may evolve to become massive early-type galaxies in the centers of the rich galaxy clusters we see today.

Molecular gas filamentary structures in galaxy clusters

AbstractRecent molecular line observations with ALMA and NOEMA in several Brightest Cluster Galaxies (BCG) have revealed the large-scale filamentary structure at the center of cool core clusters. These filaments extend over 20-100kpc, they are tightly correlated with ionized gas (Hα, [NII]) emission, and have characteristic shapes: either radial and straight, or also showing a U-turn, like a horse-shoe structure. The kinematics is quite regular and laminar, and the derived infall time is much longer than the free-fall time. The filaments extend up to the radius where the cooling time becomes larger than the infall time. Filaments can be perturbed by the sloshing of the BCG in its cluster, and spectacular cooling wakes have been observed. Filaments tend to occur at the border of cavities driven in the X-ray gas by the AGN radio jets. Observations of cool core clusters support the thermal instability scenario, which accounts for the multiphase medium in the upper atmospheres of BCG, where the right balance between heating and cooling is reached, and a chaotic cold gas accretion occurs. Molecular filaments are also seen associated to ram-pressure stripped spiral galaxies in rich galaxy clusters, and in jet-induced star formation, suggesting a very efficient molecular cloud formation even in hostile cluster environments.

Infalling groups and galaxy transformations in the cluster A2142

Context. Superclusters of galaxies provide dynamical environments for the study of the formation and evolution of structures in the cosmic web from galaxies, to the richest galaxy clusters, and superclusters themselves. Aims. We study galaxy populations and search for possible merging substructures in the rich galaxy cluster A2142 in the collapsing core of the supercluster SCl A2142, which may give rise to radio and X-ray structures in the cluster, and affect galaxy properties of this cluster. Methods. We used normal mixture modelling to select substructure of the cluster A2142. We compared alignments of the cluster, its brightest galaxies (hereafter BCGs), subclusters, and supercluster axes. The projected phase space (PPS) diagram and clustercentric distributions are used to analyse the dynamics of the cluster and study the distribution of various galaxy populations in the cluster and subclusters. Results. We find several infalling galaxy groups and subclusters. The cluster, supercluster, BCGs, and one infalling subcluster are all aligned. Their orientation is correlated with the alignment of the radio and X-ray haloes of the cluster. Galaxy populations in the main cluster and in the outskirts subclusters are different. Galaxies in the centre of the main cluster at the clustercentric distances 0.5 h−1 Mpc (Dc∕Rvir < 0.5, Rvir = 0.9 h−1 Mpc) have older stellar populations (with the median age of 10−11 Gyr) than galaxies at larger clustercentric distances. Star-forming and recently quenched galaxies are located mostly at the clustercentric distances Dc ≈ 1.8 h−1 Mpc, where subclusters fall into the cluster and the properties of galaxies change rapidly. In this region the median age of stellar populations of galaxies is about 2 Gyr. Galaxies in A2142 on average have higher stellar masses, lower star formation rates, and redder colours than galaxies in rich groups. The total mass in infalling groups and subclusters is M ≈ 6 × 1014 h−1 M⊙, that is approximately half of the mass of the cluster. This mass is sufficient for the mass growth of the cluster from redshift z = 0.5 (half-mass epoch) to the present. Conclusions. Our analysis suggests that the cluster A2142 has formed as a result of past and present mergers and infallen groups, predominantly along the supercluster axis. Mergers cause complex radio and X-ray structure of the cluster and affect the properties of galaxies in the cluster, especially at the boundaries of the cluster in the infall region. Explaining the differences between galaxy populations, mass, and richness of A2142, and other groups and clusters may lead to better insight about the formation and evolution of rich galaxy clusters.

Multiply imaged Transient Events in Cluster Lenses

ARIES had a successful gravitational microlens project during 1998-2002. A similar monitor for Transient Events in galaxies at high redshift lensed by rich galaxy-clusters provides a challenging possibility with important cosmological implications. Rich galaxy-clusters at intermediate redshifts are powerful gravitational lenses which produce multiple images, in the shape of giant arcs of 5-20" extent, of distant background galaxies in their field. Weak lens shear of the background galaxy distribution can reliably trace the lens mass profile. Multiple images of supernovae or GRBs in the background galaxies can be recorded in a systematic monitor of the system. An unlensed high redshift supernova might not be observable, but when lensed by a galaxy-cluster, it will stand out because the point event brightens relative to the host. The color profile of a high redshift lensed point event will be much more reliable than an unlensed one due to much less host contamination. An estimate of the time delay enables observation of the full light curve of the subsequent images of the event. ARIES can have outside collaboration for multiband simultaneous lightcurves of other images. The measured time delay and position of images of the transient event provide better cosmological constraints including distance scale of the Universe. The Devasthal telescope can detect one or more events by monitoring half a dozen cluster fields over three years time.

Gravitational Lensing and Microlensing in Clusters: Clusters as Dark Matter Telescopes

Gravitational lensing is brightening of background objects due to deflection of light by foreground sources. Rich clusters of galaxies are very effective lenses because they are centrally concentrated. Such natural Gravitational Telescopes provide us with strongly magnified galaxies at high redshifts otherwise too faint to be detected or analyzed. With a lensing boost, we can study galaxies shining at the end of the “Dark Ages”. We propose to exploit the opportunity provided by the large field of view and depth, to search for sources magnified by foreground clusters in the vicinity of the cluster critical curves, where enhancements can be of several tens in brightness. Another aspect is microlensing (ML), where we would like to continue our survey of a number of Galactic globular clusters over time-scales of weeks to years to search for ML events from planets to hypothesized central intermediate-mass black holes (IMBH).

Luminous quasars do not live in the most overdense regions of galaxies at z ∼ 4

Abstract We present the cross-correlation between 151 luminous quasars (MUV < −26) and 179 protocluster candidates at z ∼ 3.8, extracted from the Wide imaging survey (∼121 deg2) performed as part of the Hyper Suprime-Cam Subaru Strategic Program (HSC-SSP). We find that only two out of 151 quasars reside in regions that are more overdense compared to the average field at >4 σ. The distributions of the distances between quasars and the nearest protoclusters and the significance of the overdensity at the positions of quasars are statistically identical to those found for g-dropout galaxies, suggesting that quasars tend to reside in almost the same environment as star-forming galaxies at this redshift. Using stacking analysis, we find that the average density of g-dropout galaxies around quasars is slightly higher than that around g-dropout galaxies on 1.0–2.5 pMpc scales, while at <0.5 pMpc that around quasars tends to be lower. We also find that quasars with higher UV luminosity or with more massive black holes tend to avoid the most overdense regions, and that the quasar near-zone sizes are anti-correlated with overdensity. These findings are consistent with a scenario in which luminous quasars at z ∼ 4 reside in structures that are less massive than those expected for the progenitors of today’s rich clusters of galaxies, and possibly that luminous quasars may be suppressing star formation in their close vicinity.

MAHALO Deep Cluster Survey I. Accelerated and enhanced galaxy formation in the densest regions of a protocluster at z = 2.5

We carried out deep H$\alpha$ narrowband imaging with 10 hours net integrations towards the young protocluster, USS1558$-$003 at $z=2.53$ with the Subaru Telescope. This system is composed of four dense groups with massive local overdensities, traced by 107 H$\alpha$ emitters (HAEs) with stellar masses and dust-corrected star formation rates down to $1\times10^8$ M$_\odot$ and 3 M$_\odot$yr$^{-1}$, respectively. We have investigated the environmental dependence of various physical properties within the protocluster by comparing distributions of HAEs in higher and lower densities with a standard Kolmogorov--Smirnov test. At 97\% confidence level, we find enhanced star formation across the star-forming main sequence of HAEs living in the most extreme `supergroup', corresponding to the top quartile of overdensities. Furthermore, we derive distribution functions of H$\alpha$ luminosity and stellar mass in group and intergroup regions, approximately corresponding to 30 times and 8 times higher densities than the general field. As a consequence, we identify by 0.7 and 0.9 dex higher cutoffs in H$\alpha$ luminosity and stellar mass functions in the dense groups, respectively. On the other hand, HAEs in the intergroup environment of the protocluster show similar distribution functions to those of field galaxies despite residing in significant overdensities. In the early phase of cluster formation, as inferred from our results, the densest parts in the protocluster have had an accelerated formation of massive galaxies. We expect that these eventually grow and transform into early-type galaxies at the bright end of the red sequence as seen in present-day rich clusters of galaxies.