History of Star Formation of the Galaxy Cluster Abell 85

Abell 85 is a cD galaxy cluster in the southern hemisphere and has a redshift of 0.055. Based on the spectra of 242 member galaxies provided by the Sloan spectral survey data, using the stellar population constituents and star formation history of these member galaxies obtained from the population synthesis software STARLIGHT, we study the regularities of the variations of star formation properties of galaxies (such as the ages, metal abundances and star formation rates of the characteristic stellar populations) with the local surface density of galaxies. As revealed by the results, the galaxies situated in the highdensity environments of the central region of the cluster possess higher population ages and metal abundances, and their rates of star formation are rather low, the recent activities of star formation are obviously suppressed. Besides, the correlations of the galaxy metal abundance and speci?c star formation rate with the stellar mass are asserted.     

The Norma cluster (ACO3627) – II. The near-infrared Ks -band luminosity function

A deep   K _s   -band photometric catalogue of galaxies at the core of the rich, nearby Norma cluster (ACO3627) is presented. The survey covers about  45 × 45 arcmin²  (slightly less than 1/3 Abell radius), which corresponds to  ∼0.8  h ⁻²₇₀ Mpc²  at the adopted distance  ( v _CMB/ H ₀)  of  70  h ⁻¹₇₀ Mpc  of this cluster. The survey is estimated to be complete to a magnitude of     . This extends into the dwarf regime, 6 mag below     . The catalogue contains 390 objects, 235 of which are classified as likely or definite galaxies and 155 as candidate galaxies. The   K _s   -band luminosity function (LF) is constructed from the photometric sample, using a spectroscopic subsample to correct for fore and background contamination. We fit a Schechter function with a characteristic magnitude of     and faint-end slope of  α=−1.26 ± 0.10  to the data. The shape of the LF is similar to those found in previous determinations of the cluster LF, in both optical and near-infrared. The Schechter parameters agree well with those of recent field LFs, suggesting that the shape of both the bright-end and the faint-end slopes are relatively insensitive to environment.     

The spatial distribution of galaxies within the cosmic microwave background cold spot in the Corona Borealis supercluster

We study the spatial distribution and colours of galaxies within the region covered by the cold spot in the cosmic microwave background recently detected by the Very Small Array interpherometer (VSA) towards the Corona Borealis supercluster (CrB-SC). The spot is in the northern part of a region with a radius  ∼1° (∼5 Mpc  at the redshift of CrB-SC) enclosing the clusters Abell 2056, 2065, 2059 and 2073, and where the density of galaxies, excluding the contribution from those clusters, is approximately two times higher than the mean value in typical intercluster regions of the CrB-SC. Two of such clusters (Abell 2056 and 2065) are members of the CrB-SC, while the other two are in the background. This high-density intercluster region is quite inhomogeneous, being the most remarkable feature a large concentration of galaxies in a narrow filament running from Abell 2065 with a length of ∼35 arcmin (  ∼3 Mpc  at the redshift of CrB-SC) in the SW–NE direction. This intercluster population of galaxies probably results from the interaction of clusters Abell 2065 and 2056. The area subtended by the VSA cold spot shows an excess of faint  (21 < r < 22)  and red  (1.1 < r − i < 1.3)  galaxies as compared with typical values within the CrB-SC intercluster regions. This overdensity of galaxies shows a radial dependence and extends out to ∼15 arcmin. This could be the signature of a previously unnoted cluster in the background.     

Spatial orientations of galaxies in 10 Abell clusters of BM type II–III

We present an analysis of the spatial orientations of 1315 galaxies in 10 Abell clusters of BM type II–III (type II–III in the Bautz–Morgan system). It is found that the spin-vector orientations of the galaxies in six clusters (Abell 168, 426, 1035, 1227, 1367 and 1904) tend to lie parallel to the Local Supercluster (LSC) plane. The spin-vector projections of galaxies in six clusters (Abell 168, 1020, 1035, 1227, 1904 and 1920) are found to be oriented perpendicular with respect to the direction of the LSC centre. Three clusters (Abell 1920, 2255 and 2256) show a bimodal orientation: spin vectors tend to be oriented both parallel and perpendicular to the LSC plane. No dependence of radial velocity, distance and cluster magnitude on galaxy orientation is noticed. In a comparison with previous work, we noticed that the anisotropy might increase from early-type (BM type I) to late-type (BM types II–III and III) clusters. We notice a vanishing angular momentum for the less massive galaxy clusters (richness class 0). A significant alignment of the angular momenta of galaxies for massive clusters, e.g. the core of the Shapley Supercluster (richness class 4,   M > 10¹⁵ M_⊙  ), is found.     

Gravitational lens magnification by Abell 1689: distortion of the background galaxy luminosity function

Gravitational lensing magnifies the observed flux of galaxies behind the lens. We use this effect to constrain the total mass in the cluster Abell 1689 by comparing the lensed luminosities of background galaxies with the luminosity function of an undistorted field. Under the assumption that these galaxies are a random sample of luminosity space, this method is not limited by clustering noise. We use photometric redshift information to estimate galaxy distance and intrinsic luminosity. Knowing the redshift distribution of the background population allows us to lift the mass/background degeneracy common to lensing analysis. In this paper we use nine filters observed over 12 h with the Calar Alto 3.5-m telescope to determine the redshifts of 1000 galaxies in the field of Abell 1689. Using a complete sample of 146 background galaxies we measure the cluster mass profile. We find that the total projected mass interior to 0.25  h ⁻¹ Mpc is M _2D(<0.25  h ⁻¹ Mpc)=(0.48±0.16)×10¹⁵  h ⁻¹ M_⊙, where our error budget includes uncertainties from the photometric redshift determination, the uncertainty in the offset calibration and finite sampling. This result is in good agreement with that found by number-count and shear-based methods and provides a new and independent method to determine cluster masses.     

The influence of mergings on galaxy evolution

The evolution of the galaxy mass function MF (and luminosity function LF) depending on merging of galaxies is discussed. The richness and masses of most massive (and most luminous) galaxies of a cluster are chosen as a characteristic of the bright edge of LF. Mergers are simulated by a Monte-Carlo method. The probability of merging depends on the masses of galaxies. The ratio of the current number of galaxies to the initial one plays the role of the time scale. Transformation to real time and redshift is realized with help of the Smoluchowsky kinetic equation (SE) solution, describing the merging process and making possible to find the dependence of the galaxy number on time. The dependencies of richness, masses and magnitude differences of most massive and brightest galaxies of a cluster on redshift have been obtained. Creation of cD-galaxy has been retraced on small redshifts. The masses of the second and less massive cluster galaxies grow, but after the creation of the cD-galaxy they begin to decrease. Comparison of obtained results with data of the catalogues is provided. Correspondence in mentioned dependencies is observed. This revised version was published online in August 2006 with corrections to the Cover Date.     

Straight Arc in abell 2390

The straight arc in the galaxy-cluster Abell 2390 is investigated in the framework of a gravitational lens model that invokes a single background source galaxy. An extended source galaxy at a redshift of 0.913 is being marginally lensed by the foreground X-ray cluster of galaxies at a redshift of 0.231. It is demonstrated that a single lensed galaxy lying on or very near to the lip caustic of the cluster lens is capable of reproducing the linear morphology with the observed breaks.     

Star Formation Properties of the Galaxy Cluster Abell 2199

Through the morphological classifications for 290 member galaxies in the nearby galaxy Abell 2199, the star formation rates and their relations with their morphology and related physical properties are investigated in this paper. It is found that the typical star formation rate in galaxies of this galaxy cluster is strongly correlated with the H_α equivalent width, and the degree of discontinuity of the galaxy spectrum at 4000 Å is also strongly correlated with the stellar mass included in the galaxy. It is also found that star formation activities in these galaxies do not exhibit the obvious circumstance effect. This result indicates that this galaxy cluster is still situated at the stage of the violent dynamical evolution and far from the dynamical equilibrium.     

星系团的分层效应

对星系团各类分层效应的有关问题做了概要的评述,包括成员星系在位置空间和(或)速度空间中的形态分层、光度(质量)分层和元素丰度分层的表现形式和探测途径,分层效应可能的形成机制及其对星系和星系团的结构和演化的影响。     

Local Environmental Dependence of Galaxy Properties in a Volume-Limited Sample of Main Galaxies

Using a volume-limited sample of Main Galaxies from SDSS Data Release 5,we investigate the dependence of galaxy properties on local environment.For each galaxy,a local three-dimensional density is calculated.We find that the galaxy morphological type depends strongly on the local environment:galaxies in dense environments have predominantly early type morphologies.Galaxy colors have only a weak dependence on the environment.This puts an important constraint on the process of galaxy formation.     

Essential properties of the cD galaxy in Abell 1795 — I. General optical and X-ray structure,dynamics and formation

We investigate current problems connected with the formation of cD galaxies. The subject of the present paper is to compare internal properties of the cD galaxy Zw162010 with cluster properties of Abell 1795. This consideration is a first attempt to find commonly valid essential correlations between peculiarities of brightest cluster members as structures and active phenomena and global cluster properties as for instance galaxy populations and concentration degrees. The colours, the X-ray emission, and the velocity of the cD galaxy are used to discuss the obvious influence of the environment on the evolution of the active nucleus. In a second paper (Kirchner et al. 1992) the radio structure is used to investigate the influence of the surrounding cluster medium onto the development of the active nucleus. Furtheron, various jet ejection scenarios will be quantitatively examined.     

Selection,Statistics and Photometry of Compact Galaxies with Different Instrumental Equipment,Part II. The Cluster Abell 1775

In continuation of part I of our investigation a field of 0.8 near the galactic north pole is investigated with two large photographic telescopes of very different optical constants. The field contains the cluster Abell 1775. Statistics and photometry confirm the results of part I. The fraction of optical compact galaxies up to the identification magnitude 18^m9 (B) is found to be more than 30% of the total number of cluster galaxies. The data for a secondary photometric sequence, which had to be determined for the photometry of the galaxies, are presented.     

The nature of the dwarf population in Abell 868

We present the results of a study of the morphology of the dwarf galaxy population in Abell 868, a rich, intermediate-redshift     cluster which has a galaxy luminosity function (LF) with a steep faint-end slope     . A statistical background subtraction method is employed to study the     colour distribution of the cluster galaxies. This distribution suggests that the galaxies contributing to the faint-end of the measured cluster LF can be split into three populations: dwarf irregular galaxies (dIrrs) with     dwarf elliptical galaxies (dEs) with     and contaminating background giant ellipticals (gEs) with     . The removal of the contribution of the background gEs from the counts only marginally lessens the faint-end slope     . However, the removal of the contribution of the dIrrs from the counts produces a flat LF     . The dEs and the dIrrs have similar spatial distributions within the cluster, except that the dIrrs appear to be totally absent within a central projected radius of about 0.2 Mpc     . The number densities of both dEs and dIrrs appear to fall off beyond a projected radius of ≃ 0.35 Mpc. We suggest that the dE and dIrr populations of A868 have been associated with the cluster for similar time-scales, but evolutionary processes such as 'galaxy harassment' tend to fade the dIrr galaxies while having a much smaller effect on the dE galaxies. The harassment would be expected to have the greatest effect on dwarfs residing in the central parts of the cluster.     

Environmental dependence of five photometric band concentration indexes for luminous red galaxies from the SDSS Data Release 7

Using the Luminous Red Galaxy (LRG) sample of the Sloan Digital Sky Survey Data Release 7 (SDSS DR7), we explore the environmental dependence of five photometric band concentration indexes of LRGs. It turns out that the trends for all the five band concentration indexes to change with the local density are the same: galaxies with higher concentration reside preferentially in overdense environments, while galaxies with lower concentration are located preferentially in underdense environments (© 2010 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Dynamical Substructures of Galaxy Cluster Abell 85

Abell 85 is a cD cluster of galaxies with the redshift of 0.055 in the southern hemisphere. Based on the spectroscopic data obtained by predecessors and the data of the SDSS (Sloan Digital Sky Survey), 370 member galaxies of the cluster are sieved by means of the 3σ method and their dynamical states are analyzed. From the spatial distribution and the local line-of-sight velocity distribution of these member galaxies it is found that this cluster of galaxies contains 4 clear substructures and they are just in the process of pairwise coalescence. This shows that the cluster Abell 85 is in the actively dynamical state, far from reaching the dynamical equilibrium.     

An attempt to test Ambartsumian's idea of the origin of the galaxy . II. location of galaxies within clusters and galaxy position angles

The location of galaxies in 377 rich Abell galaxy clusters is discussed. We compared the distributions of galaxies in the sample containing all galaxies with the sample compiled from the 20 brightest objects. Counts in circular sectors with angle width equal to 30î show isotropy. Only in the case of BM I clusters and the coordinate system related to the cluster major axis did we find anisotropic distributions. We investigated also the distributions of galaxy position angles within clusters exhibiting isotropy. The structure position angles for both samples have been studied as well. They appeared to be different. The difference in location of galaxies in the case of cD clusters, as well as the more elliptical shape and different position angles of samples containing bright galaxies is observed.     

Spin vector orientation of galaxies in the region 15h 48m≤α(2000) ≤ 19h 28m, −68°≤δ(2000) ≤−62°

We present an analysis of the orientations of 1433 galaxies found in the region  15^h 48^m≤α(2000) ≤ 19^h 28^m, −68°≤δ(2000) ≤−62°  . In this region we investigated three Abell clusters (S0794, S0797, S0805) of richness Class 0 and the Triangulum Australis cluster. Our aim is to examine non-random effects in galaxy orientations in clusters. In addition, we classified the investigated galaxies into subsamples on the basis of their axial ratio, major diameter and morphology. The spin vector orientations of total galaxies in the investigated region is found to be random. No preferred orientation is found in the clusters. We could not note any morphological dependence of the galaxy orientations in our samples. No preferred orientations can be seen for the spiral galaxies. The morphologically unidentified galaxies, galaxies having major diameters of <47 arcsec, and the nearly edge-on galaxies  ( b / a < 0.5, 0.4 < b / a ≤ 0.5)  show anisotropy: spin vectors of galaxies tend to be oriented perpendicular to the Local Supercluster plane and spin vector projections tend to point radially with respect to the Virgo cluster centre.     

Environmental effects on galaxy luminosity functions: the cluster Abell 496

We have derived the galaxy luminosity function in various regions of the cluster of galaxies Abell 496 from a wide field image in the I band. A Schechter function fit in the 17≤ I_AB ≤22(–19.5≤ M_IAB ≤ –14.5) magnitude interval gives a steep power law index, which is somewhat steeper in the outer regions than in the inner zones. This result agrees with previous findings obtained by several teams on the Coma cluster and can be interpreted as due to the fact that faint galaxies are accreted by large ones in the central regions. This revised version was published online in July 2006 with corrections to the Cover Date.     

Compilation of nearby northern Abell clusters (z < 0.1) with central dominant galaxies

We compiled informations with respect to optical structures, X-ray structures, cooling flow properties, and X-ray luminosities, respectively, for 342 nearby northern Abell clusters with central dominant galaxies.     

The Hα Luminosity Functions of Nearby Clusters of Galaxies

We present a deep wide field Hα imaging survey of the central regions of the two nearby clusters of galaxies Coma and Abell 1367, taken with the WFC at the INT 2.5m telescope. We determine for the first time the Schechter parameters of the Hα luminosity function (LF) of cluster galaxies. The Hα LFs of Abell 1367 and Coma are compared with each other. Typical parameters of φ ≈ 10^0.00±0.07 Mpc^-3, L ^*≈ 10^41.25±0.05 erg sec^-1 and α ≈ -0.70±0.10 are found for both clusters. This revised version was published online in September 2006 with corrections to the Cover Date.