Brightest Member Galaxies Research Articles

The Emergence of a Brightest Cluster Galaxy in a Protocluster Core at z = 2.24

We report the detection of a pair of massive quiescent galaxies likely in the process of merging at the center of the spectroscopically confirmed, extremely massive protocluster BOSS1244 at z = 2.24 ± 0.02. These galaxies, BOSS1244-QG1 and BOSS1244-QG2, were detected with Hubble Space Telescope grism slitless spectroscopic observations. These two quiescent galaxies are among the brightest member galaxies, with z = 2.223–2.255 in BOSS1244, and reside at redshifts z = 2.244 and z = 2.242, with a half-light radius of 6.76 ± 0.50 kpc and 2.72 ± 0.16 kpc, respectively. BOSS1244-QG1 and BOSS1244-QG2 are separated by a projected distance of about 70 physical kpc, implying that the two galaxies likely merge to form a massive brightest cluster galaxy (BCG) with size and mass similar to the most massive BCGs in the local Universe. We thus infer that BCG formation through dry major mergers may happen earlier than the full assembly of a cluster core, which broadens our previous understanding of the coevolution of mature galaxy clusters and BCGs in the nearby Universe. Moreover, we find a strong density–star formation relation over a scale of ∼18 comoving Mpc in BOSS1244, i.e., star formation activity decreases as density increases, implying that the quenching of star formation in BCGs and their progenitors is likely governed by environment-related processes before the virialization of the cluster core.

Identification of clusters of galaxies and physical properties of clusters and their member galaxies

Clusters of galaxies are the largest gravitationally bound systems in the Universe and are located at the knots of cosmic web. They provide powerful constraints on galaxy evolution, the formation of large scale structure of the Universe and many astrophysical processes. This paper summarizes the results we obtained in the last decade on identification of galaxy clusters, studies of the properties of clusters and cluster member galaxies. We developed a method to identify galaxy clusters by using photometric redshifts of galaxies. The method was applied to the survey data of Sloan Digital Sky Survey (SDSS), and we identified 39668 clusters from the sixth data release of SDSS, and later identified 158103 clusters from the twelfth data release of SDSS, which doubles the number of known clusters and extends the redshift range of clusters from 0.3 to 0.8. Recently, we identified 47600 clusters from all sky data of Two Micron All-Sky Survey (2MASS), Wide-field Infrared Survey Explorer (WISE) and SuperCOSMOS, which significantly enlarge the number of clusters outside of the SDSS sky region. More high-redshift clusters were also recently identified from SDSS×WISE and the deep survey data, which significantly enlarge the number of cluster at high redshift. By inspecting the SDSS color images, we found many clusters showing giant arcs, acting as the lensed system for background galaxies. Many following-up studies have been done to understand the properties of galaxy clusters, including their spatial distribution in the Universe, the dynamical state and diffuse radio emission. The two point correlation function of 79091 clusters was calculated to detect the Baryon Acoustic Oscillations (BAO) signal with 3.7σ confidence, which is the first significant detection of the BAO signal by using galaxy clusters as tracers. Based on optical photometric data, we developed a method to quantify the dynamical state of clusters and calculated the relaxation parameter for 2092 rich clusters. We found that the cluster dynamical state is significantly correlated with the absolute magnitude of Brightest Cluster Galaxy (BCG) and also depends on the magnitude difference between the first BCG and the second BCG. The diffuse radio emission of galaxy clsuters detected in merging clusters is related to dynamical state, so that the radio power of diffuse radio emission, cluster mass proxy and dynamical parameters form a fundamental plane. The properties of cluster member galaxies have been investigated in several aspects. By using 2092 clusters with dynamical states, we calculated the composite luminosity function of member galaxies. We found that more relaxed clusters have fewer bright member galaxies, but host a brighter BCG. By cross-matching the largest optical cluster sample with radio data obtained by the Very Large Array (VLA) of National Radio Astronomy Observatory (NRAO) through the NRAO VLA Sky Survey (NVSS) and Faint Images of the Radio Sky at Twenty-centimeters (FIRST), we got the largest complete sample of radio loud BCG. We obtained the radio luminosity function of BCGs, and found that it is related to the optical luminosity of BCG and dynamical state of clusters. BCGs with larger optical luminosity have higher fraction of radio loud. BCGs in more relaxed clusters have higher radio power. It is gareat era now as more deeper sky surveys on many bands are going on. We expect many breakthroughs in the research areas related to galaxy clusters.

Testing redMaPPer centring probabilities using galaxy clustering and galaxy–galaxy lensing

Galaxy cluster centring is a key issue for precision cosmology studies using galaxy surveys. Mis-identification of central galaxies causes systematics in various studies such as cluster lensing, satellite kinematics, and galaxy clustering. The red-sequence Matched-filter Probabilistic Percolation (redMaPPer) estimates the probability that each member galaxy is central from photometric information rather than specifying one central galaxy. The redMaPPer estimates can be used for calibrating the off-centring effect, however, the centring algorithm has not previously been well-tested. We test the centring probabilities of redMaPPer cluster catalog using the projected cross correlation between redMaPPer clusters with photometric red galaxies and galaxy-galaxy lensing. We focus on the subsample of redMaPPer clusters in which the redMaPPer central galaxies (RMCGs) are not the brightest member galaxies (BMEM) and both of them have spectroscopic redshift. This subsample represents nearly 10% of the whole cluster sample. We find a clear difference in the cross-correlation measurements between RMCGs and BMEMs, and the estimated centring probability is 74$\pm$10% for RMCGs and 13$\pm$4% for BMEMs in the Gaussian offset model and 78$\pm$9% for RMCGs and 5$\pm$5% for BMEMs in the NFW offset model. These values are in agreement with the centring probability values reported by redMaPPer (75% for RMCG and 10% for BMEMs) within 1$\sigma$. Our analysis provides a strong consistency test of the redMaPPer centring probabilities. Our results suggest that redMaPPer centring probabilities are reliably estimated. We confirm that the brightest galaxy in the cluster is not always the central galaxy as has been shown in previous works.

Brightest galaxies as halo centre tracers in SDSS DR7

Abstract Determining the positions of halo centres in large-scale structure surveys is crucial for many cosmological studies. A common assumption is that halo centres correspond to the location of their brightest member galaxies. In this paper, we study the dynamics of brightest galaxies with respect to other halo members in the Sloan Digital Sky Survey DR7. Specifically, we look at the line-of-sight velocity and spatial offsets between brightest galaxies and their neighbours. We compare those to detailed mock catalogues, constructed from high-resolution, dark-matter-only N-body simulations, in which it is assumed that satellite galaxies trace dark matter subhaloes. This allows us to place constraints on the fraction fBNC of haloes in which the brightest galaxy is not the central. Compared to previous studies, we explicitly take into account the unrelaxed state of the host haloes, velocity offsets of halo cores and correlations between fBNC and the satellite occupation. We find that fBNC strongly decreases with the luminosity of the brightest galaxy and increases with the mass of the host halo. Overall, in the halo mass range 1013–1014.5 h− 1M⊙ we find fBNC ∼ 30 per cent, in good agreement with a previous study by Skibba et al. We discuss the implications of these findings for studies inferring the galaxy–halo connection from satellite kinematics, models of the conditional luminosity function and galaxy formation in general.

Properties of Brightest Cluster Galaxies as a Function of Cluster Classification Type

We classified Abell clusters using the magnitude differences between two or three bright member galaxies and investigated how such classification was correlated with the properties of brightest cluster galaxies (BCGs). S-type BCGs being clearly brighter than the rest of the member galaxies were likely to be red, luminous, and evolved as early type galaxies. On the other hand, T-type BCGs being not dominant at all were less luminous than early type galaxies. A small fraction of BCGs was currently forming stars, and all of the star-forming BCGs were T-type BCGs. Active galactic nuclei were most frequent for S-type BCGs. Through these quantitative analyses of the BCG properties, we discussed the possible scenario of BCG formation and the differences between S-type and T-type of BCGs.

GALAXIES IN X-RAY GROUPS. II. A WEAK LENSING STUDY OF HALO CENTERING

Locating the centers of dark matter halos is critical for understanding the mass profiles of halos as well as the formation and evolution of the massive galaxies that they host. The task is observationally challenging because we cannot observe halos directly, and tracers such as bright galaxies or X-ray emission from hot plasma are imperfect. In this paper we quantify the consequences of miscentering on the weak lensing signal from a sample of 129 X-ray selected galaxy groups in the COSMOS field with redshifts 0<z<1 and halo masses in the range 10^13 - 10^14 M_sun. By measuring the stacked lensing signal around eight different candidate centers (such as the brightest member galaxy, the mean position of all member galaxies, or the X-ray centroid), we determine which candidates best trace the center of mass in halos. In this sample of groups, we find that massive galaxies near the X-ray centroids trace the center of mass to <~75 kpc, while the X-ray position and centroids based on the mean position of member galaxies have larger offsets primarily due to the statistical uncertainties in their positions (typically ~50-150 kpc). Approximately 30% of groups in our sample have ambiguous centers with multiple bright or massive galaxies, and these groups show disturbed mass profiles that are not well fit by standard models, suggesting that they are merging systems. We find that halo mass estimates from stacked weak lensing can be biased low by 5-30% if inaccurate centers are used and the issue of miscentering is not addressed.

Metallicity of the Fossil Group NGC 1550 Observed with Suzaku

Abstract We studied the temperature and metal abundance distributions of the intra-cluster medium (ICM) in a group of galaxies, NGC 1550, observed with Suzaku. NGC 1550 is classified as a fossil group, which has few bright member galaxies, except for the central galaxy. Thus, such a type of galaxy is important to investigate how metals are enriched to the ICM. With the Suzaku XIS instrument, we directly measured not only the Si, S, and Fe lines, but also the O and Mg lines, and obtained those abundances to an outer region of $\sim\ $0.5$r_{180}$ for the first time, and confirmed that the metals in the ICM of such a fossil group are indeed extending to a large radius. We found steeper gradients for the Mg, Si, S, and Fe abundances, while O showed an almost flat abundance distribution. Abundance ratios of $\alpha$-elements to Fe were similar to those of the other groups and poor clusters. We calculated the number ratio of type II to type Ia supernovae for the ICM enrichment to be 2.9$\ \pm\ $0.5 within 0.1$r_{180}$; the value is consistent with those for the other groups and poor clusters observed with Suzaku. We also calculated the metal mass-to-light ratios (MLRs) for Fe, O, and Mg with the $B$-band and $K$-band luminosities of the member galaxies of NGC 1550. The derived MLRs are comparable to those of the NGC 5044 group in the $r$$&amp;lt;$ 0.1$r_{180}$ region, while those of NGC 1550 are slightly higher than those of NGC 5044 in the outer region.

COLORS, AGES, AND METALLICITIES OF GALAXIES IN SIX NEARBY GALAXY CLUSTERS

We present an optical-infrared photometric study of galaxies in six nearby clusters of galaxies at <TEX>$z=0.041{\sim}0.098$</TEX> (A1436, A1773, A1809, A2048, A2142, and A2152). Using BV I photometry obtained at the Bohyunsan Optical Astronomical observatory and <TEX>$JHK_S$</TEX> photometry extracted from the 2-Micron All-Sky Survey catalog, we investigate the colors of galaxies in the clusters. Using the (B - V) versus (<TEX>$I\;-\;K_S$</TEX>) color-color diagrams in comparison with the simple stellar population model, we estimate the ages and metallicities of bright early-type member galaxies. Early-type galaxies in each cluster show the color-magnitude relation. Ages and metallicities of early-type members show little dependence on their velocity dispersions. Mean ages of early-types in the clusters range from 3 Gyr to 20 Gyr, showing a large dispersion, and mean metallicities range from Z = 0.03 to 0.05 above the solar value, showing a negligible dispersion.

The Principal Axis of the Virgo Cluster

Using accurate distances to individual Virgo Cluster galaxies obtained by the method of surface brightness fluctuations, we show that Virgo's brightest elliptical galaxies have a remarkably collinear arrangement in three dimensions. This axis, which is inclined by ~10°-15° from the line of sight, can be traced to even larger scales where it appears to join a filamentary bridge of galaxies connecting Virgo to the rich cluster Abell 1367. The orientations of individual Virgo elliptical galaxies also show some tendency to be aligned with the cluster axis, as does the jet of the supergiant elliptical galaxy M87. These results suggest that the formation of the Virgo Cluster, and its brightest member galaxies, have been driven by infall of material along the Virgo-A1367 filament.

Superclustering at high redshifts

view Abstract Citations (15) References (270) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Superclustering at High Redshifts West, Michael J. Abstract Evidence is presented which suggests that the radio emission from distant quasars and radio galaxies is not randomly directed, but rather has preferred orientations with respect to surrounding large-scale structures. Specifically, the radio major axes of high-redshift sources exhibit a significant tendency to point in the direction of neighboring quasars and radio galaxies, for separations up to ~45h^-1^ Mpc (comoving). This alignment phenomenon is very similar to that seen at low redshifts between neighboring rich clusters and their brightest member galaxies, which suggests that what is being seen here is tentative evidence of the existence of a filamentary pattern of superclustering at redshifts z ~ 1 or more. If the alignment effect found here is confirmed with larger and more homogeneous samples, then the orientations of extragalactic radio sources may provide a very useful probe of large- scale structure at high redshifts. These results may also help shed some light on the recently discovered tendency for the extended radio and optical emissions from high redshift radio sources to be aligned. Publication: The Astrophysical Journal Pub Date: September 1991 DOI: 10.1086/170481 Bibcode: 1991ApJ...379...19W Keywords: Extragalactic Radio Sources; Galactic Clusters; Galactic Evolution; Quasars; Red Shift; Alignment; Cosmology; Radio Emission; Astrophysics; COSMOLOGY; GALAXIES: CLUSTERING; GALAXIES: FORMATION; QUASARS; RADIO SOURCES: GALAXIES full text sources ADS | data products NED (135) SIMBAD (132)

Alignment of Clusters with Brightest Member Galaxies

We have obtained CCD images of the brightest elliptical galaxy in 27 clusters of galaxies with redshifts z &lt; 0.1. For each galaxy we fitted elliptical isophotes to the galaxy image. We also measured the position angle of each cluster from the Palomar Observatory Sky Survey (POSS) prints. We find only marginal evidence for alignment of brightest cluster members (BCM) with their parent clusters, but we find that our CCD isophotes are well aligned with the POSS image.

Spectra and Other Characteristics of Interconnected Galaxies and of Galaxies in Groups and in Clusters. III.

view Abstract Citations (57) References (6) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Spectra and Other Characteristics of Interconnected Galaxies and of Galaxies in Groups and in Clusters. III. Zwicky, F. ; Humason, M. L. Abstract An observational and theoretical analysis of the medium compact cluster of galaxies around NGC 541 has been initiated. The cluster, in an area of four square degrees, contains about five hundred galaxies whose apparent photographic magnitudes lie in the range 13A <[rn < 19.0. The positions and magnitudes of eighty-five cluster members have been determined. Their distribution confirms the exponential luminosity function which was previously established from the study of the populations of 704 rich clusters of galaxies. The surface brightness of the above-mentioned cluster galaxies is plotted in dependence upon their magnitudes, indicating both decreasing and increasing surface brightness with increasing magnitude. This is related to the discovery, recently made, of a relatively great number of very compact and absolutely faint galaxies. Structural and spectral types of the galaxies of the cluster studied are remarkably uniform, pointing to a very old age and a stationary character of the cluster. The average symbolic velocity of recession of forty-one cluster galaxies is (Vs) = 5321 km/sec and the dispersion ((A V5) 2)112 is 406 km/sec. From the analysis of the spatial distribution of the values of V it follows that the cluster is not sensibly rotating, although it is elliptical in shape. From the spatial distribution of the values of the velocity dispersion it may be concluded that the cluster is not expanding. The fact that the fainter galaxies have a greater velocity dispersion than the brighter galaxies indicates a tendency toward the establishment of equipartition of energy among at least the brighter cluster galaxies. The indicative distance of the cluster, the indicative absolute photographic magnitude of its brightest member galaxy and the relative indicative mass4uminsity ratio, as determined from the Virial theorem, are respectively, D* = 53.2 million pc, M* = -20.2 and )? 100. This value of lies midway between those found for individual bright galaxies and those of very richly populated compact clusters of galaxies. Suggestions are discussed of how might be found to be drastically reduced because of the presence of various types of as yet undetected types of intergalactic matter. For the past four years the cluster around NGC 541 has been searched for supernovae with the 48-inch Schmidt telescope. As a result of this search one supernova of Type I has been found in the member galaxy IC 1703 of the cluster on January 22, 1963. Publication: The Astrophysical Journal Pub Date: January 1964 DOI: 10.1086/147752 Bibcode: 1964ApJ...139..269Z full text sources ADS | data products NED (86) SIMBAD (85) Related Materials (3) Part 1: 1960ApJ...132..627Z Part 2: 1961ApJ...133..794Z Part 4: 1964ApJ...139.1393Z