Investigation of Galaxy Distribution in 10 Clusters

The number density distributions for further 10 clusters of galaxies were derived by counting galaxies on the red Palomar Sky Survey prints. For 6 clusters the radial number density distribution and the radial cumulative galaxy distribution were derived.     

Investigation of nine clusters of galaxies

The number-density distributions of further 9 clusters of galaxies were derived by counting galaxies on the red Palomar Sky Survey prints. For all the clusters the radial number density distribution and the radial cumulative galaxy distribution were calculated.     

Investigation of Galaxy Distribution in the Ursa Major Supercluster of Galaxies

The number density distribution of galaxies in the region of the UMa Supercluster of galaxies was derived by counting galaxies on the red Palomar Sky Survey prints. For fourteen clusters in this region the radial number density distribution and the radial cumulative galaxy distribution were calculated.     

Further investigations of clusters of galaxies

The number-density distributions of ten further clusters of galaxies were derived by counting galaxies on the red Polomar Sky Survey prints. For eight isolated clusters the radial number-density distributions and the radial cumulative galaxy distributions were calculated.     

Secondary maxima in the radial galaxy distribution of clusters of galaxies and subclustering

From the structural investigations of 19 clusters of galaxies follows that secondary maxima in their projected radial galaxy distributions can be explained by subclustering. There are no signs for density shells around the cluster centres. Subclustering seems to be a typical phenomenon in clusters of galaxies.     

Distribution of Galaxies in 10 Clusters

The number-density distributions for further 10 clusters of galaxies were derived by counting galaxies on the red Palomar Sky Survey prints. For 9 clusters the radial number-density distribution and the radial cumulative galaxy distribution were calculated.     

Investigation of 10 additional clusters of galaxies

The number-density distributions of further 10 clusters of galaxies were derived by counting galaxies on the red Palomar Sky Survey prints. For all the clusters the radial number-density distribution and the radial cumulative galaxy distribution were calculated.     

Analysis of the spatial distribution of gamma-ray bursts in their host galaxies

We compare the radial distributions of known localized gamma-ray bursts (GRBs) relative to the centers of their host galaxies with the distributions of known objects in nearby galaxies (supernovae of various types, X-ray binaries), the hypothetical dark-matter profiles, and the distribution of luminous matter in galaxies in the model of an exponential disk. By comparing the moments of empirical distributions, we show that the radial distribution of GRBs in galaxies differs significantly from that of other sources. We suggest a new statistical method for comparing empirical samples that is based on estimating the number of objects within a given radius. The exponential disk profile was found to be in best agreement with the radial distribution of GRBs. The distribution of GRBs relative to the centers of their host galaxies also agrees with the dark matter profile at certain model parameters.     

On the evolution of the SFR in galactic disks

A simple semi-empirical model of the evolution of observed ring-shaped radial distributions of SFR surface density in galaxies NGC 628 and NGC 6946 provides us with exponential stellar disks with cooresponding scale length of the surface brightness radial distributions and constraints for the some nonobservable parameters: characteristic SFR decreasing time scale, characteristic collapse time scale, etc. This revised version was published online in August 2006 with corrections to the Cover Date.     

The properties of the galaxies in the ENACS clusters, and the relation between spirals and S0 galaxies

We discuss the properties of the galaxies in about 60 rich, nearby clusters, using kinematic data from the ESO Nearby Abell Cluster Survey, combined with new imaging data. The images were used to classify the galaxies, and to recalibrate the galaxy types derived from the ENACS spectra; this yields galaxy-type estimates for about4800 galaxies. For about 1200 galaxies, a bulge/disk decomposition could be made, which yields sizes and luminosities of bulges and disks. From the projected radial distances and relative l.o.s.-velocities we derived the galaxy ensembles with significantly different phase-space distributions. We find that galaxies in and outside substructure must be distinguished. The morphological composition of the substructures appears to vary with projected radius. Outside substructures, 4 galaxy ensembles must be defined: viz. the brighest Es, the other early-type galaxies, the early spirals(Sa-Sb), and the late spirals (including the emission-line galaxies). We also study the morphology-density relation, and we find that the segregation of the late spirals is driven mostly by global factors, while the segregation of Es, S0s and early spirals is driven mostly by local density. The properties of early spirals and S0ssupport the picture in which early spirals transform into S0s, while the properties of the late spirals do not support such a relation. This revised version was published online in July 2006 with corrections to the Cover Date.     

The asymmetry of the Coma cluster of galaxies

A detailed reinvestigation of the Coma cluster basing on enlarged observational material of number density distributions and radial velocities of galaxies as well as radio and x-ray data is performed and supports our previous conclusion that this cluster possesses a substructure. This substructure is in the south-western region of the cluster and produces the impression of an elongated cluster structure in the direction of the bridge between Coma and A 1367. A 1656 seems to be a cD-like cluster with NGC 4874 as the only dominating giant central galaxy.     

Statistical properties of the spatial distribution of galaxies

The methods of determining the fractal dimension and irregularity scale in simulated galaxy catalogs and the application of these methods to the data of the 2dF and 6dF catalogs are analyzed. Correlation methods are shown to be correctly applicable to fractal structures only at the scale lengths from several average distances between the galaxies, and up to (10 ? 20)% of the radius of the largest sphere that fits completely inside the sample domain. Earlier the correlation methods were believed to be applicable up to the entire radius of the sphere and the researchers did not take the above restriction into account while finding the scale length corresponding to the transition to a uniform distribution. When an empirical formula is applied for approximating the radial distributions in the samples confined by the limiting apparent magnitude, the deviation of the true radial distribution from the approximating formula (but not the parameters of the best approximation) correlate with fractal dimension. An analysis of the 2dF catalog yields a fractal dimension of 2.20 ± 0.25 on scale lengths from 2 to 20 Mpc, whereas no conclusive estimates can be derived by applying the conditional density method for larger scales due to the inherent biases of the method. An analysis of the radial distributions of galaxies in the 2dF and 6dF catalogs revealed significant irregularities on scale lengths of up to 70 Mpc. The magnitudes and sizes of these irregularities are consistent with the fractal dimension estimate of D =2.1–2.4.     

Density and Radial Velocity Strucutre of the Hydra I Cluster of Galaxies

The investigation of the distributions of number densities, radial velocities and morphological types in the Hydra I cluster led us to the conclusion that this cluster possesses dominant substructures. This result is in agreement with former conclusions of different authors that substructures are a typical phenomenon for a high percentage of all clusters of galaxies. The galaxies inside the radius 60 from the cluster centre giv ea mean cluster redshift 3332±102 km/s and a velocity dispersion 679 ± 87 km/s.     

On the Structure of the Coma Cluster of Galaxies

The investigation of the distributions of number densities and radial velocities in the Coma cluster led us to the conclusion that this cluster possesses substructures. This result is in agreement with corresponding results for the Hydra I cluster and the Perseus cluster and with former conclusions by different authors that substructures are a typical phenomenon for a high percentage of all clusters of galaxies.     

The abundance and radial distribution of satellite galaxies

Using detailed mock galaxy redshift surveys (MGRSs) we investigate the abundance and radial distribution of satellite galaxies. The mock surveys are constructed using large numerical simulations and the conditional luminosity function (CLF), and are compared against data from the Two Degree Field Galaxy Redshift Survey (2dFGRS). We use Monte Carlo Markov chains to explore the full posterior distribution of the CLF parameter space, and show that the average relation between light and mass is tightly constrained and in excellent agreement with our previous models and with that of Vale & Ostriker. The radial number density distribution of satellite galaxies in the 2dFGRS reveals a pronounced absence of satellites at small projected separations from their host galaxies. This is (at least partly) owing to the overlap and merging of galaxy images in the 2dFGRS parent catalogue. Owing to the resulting close-pair incompleteness we are unfortunately unable to put meaningful constraints on the radial distribution of satellite galaxies; the data are consistent with a radial number density distribution that follows that of the dark matter particles, but we cannot rule out alternatives with a constant number density core. Marginalizing over the full CLF parameter space, we show that in a ΛCDM concordance cosmology the observed abundances of host and satellite galaxies in the 2dFGRS indicate a power spectrum normalization of  σ₈≃ 0.7  . The same cosmology but with  σ₈= 0.9  is unable to match simultaneously the abundances of host and satellite galaxies. This confirms our previous conclusions based on the pairwise peculiar velocity dispersions and the group multiplicity function.     

On the formation of massive galaxies: a simultaneous study of number density, size and intrinsic colour evolution in GOODS

The evolution of number density, size and intrinsic colour is determined for a volume-limited sample of visually classified early-type galaxies selected from the Hubble Space Telescope /Advanced Camera for Surveys images of the Great Observatories Origins Deep Survey (GOODS) North and South fields (version 2). The sample comprises 457 galaxies over 320 arcmin² with stellar masses above  3 × 10¹⁰ M_⊙  in the redshift range  0.4 < z < 1.2  . Our data allow a simultaneous study of number density, intrinsic colour distribution and size. We find that the most massive systems  (≳3 × 10¹¹ M_⊙)  do not show any appreciable change in comoving number density or size in our data. Furthermore, when including the results from 2dF galaxy redshift survey, we find that the number density of massive early-type galaxies is consistent with no evolution between   z = 1.2  and 0, i.e. over an epoch spanning more than half of the current age of the Universe. We find large discrepancies between the predictions of semi-analytic models. Massive galaxies show very homogeneous intrinsic colour distributions, with nearly flat radial colour gradients, but with a significant negative correlation between stellar mass and colour gradient, such that red cores appear predominantly in massive galaxies. The distribution of half-light radii – when compared to   z ∼ 0  and   z > 1  samples – is compatible with the predictions of semi-analytic models relating size evolution to the amount of dissipation during major mergers.     

Radial HI profiles at the periphery of galactic disks: The role of ionizing background radiation

Observations of neutral hydrogen in spiral galaxies reveal a sharp cutoff in the radial density profile at some distance from the center. Using 22 galaxies with known HI distributions as an example, we discuss the question of whether this effect can be associated exclusively with external ionizing radiation, as is commonly assumed. We show that before the surface density reaches δ _HI ≤ 0.5 M _⊙ pc⁻² (the same for galaxies of different types), it is hard to expect the gas to be fully ionized by background radiation. For two of 13 galaxies with a sharp drop in the HI profile, the “steepening” can actually be caused by ionization. At the same time, for the remaining galaxies, the observed cutoff in the radial HI profile is closer to the center than if it was a consequence of ionization by background radiation and, therefore, it should be caused by other factors.     

Rotational mixing in early-type main-sequence stars

We present N -body simulations of galaxy groups embedded in a common halo of matter. We study the influence of the different initial conditions upon the evolution of the group and show that denser configurations evolve faster, as expected. We then concentrate on the influence of the initial radial density profile of the common halo and of the galaxy distribution. We select two kinds of density distributions, a singular profile (modelled by a Hernquist distribution) and a profile with a flat core (modelled by a Plummer sphere). In all cases we witness the formation of a central massive object owing to mergings of individual galaxies and to accretion of stripped material, but both its formation history and its properties depend heavily on the initial distribution. In Hernquist models the formation is caused by a 'burst' of mergings in the inner parts, owing to the large initial concentration of galaxies in the centre. The merging rate is much slower in the initial phases of the evolution of a Plummer distribution, where the contribution of accretion to the formation of the central object is much more important. The central objects formed within Plummer distributions have projected density profiles which are not in agreement with the radial profiles of observed brightest cluster members, unless the percentage of mass in the common halo is small. In contrast, the central object formed in initially cusped models has projected radial profiles in very good agreement with those of brightest cluster members, sometimes also showing luminosity excess over the r ^1/4 law in the outer parts, as is observed in cD galaxies.     

The SAI catalog of supernovae and radial distributions of supernovae of various types in galaxies

We describe the Sternberg Astronomical Institute (SAI) catalog of supernovae. We show that the radial distributions of type-Ia, type-Ibc, and type-II supernovae differ in the central parts of spiral galaxies and are similar in their outer regions, while the radial distribution of type-Ia supernovae in elliptical galaxies differs from that in spiral and lenticular galaxies. We give a list of the supernovae that are farthest from the galactic centers, estimate their relative explosion rate, and discuss their possible origins.     

Method for analyzing the spatial distribution of galaxies on gigaparsec scales. II. Application to a grid of the HUDF-FDF-COSMOS-HDF surveys

The initial principles of a method for analyzing the spatial distribution of visible matter in the universe with structures on size scales of thousands of Mpc are discussed. This method is based on analyzing the distribution N(z) of the photometric redshifts of galaxies in deep fields using large bins Δ z=0.1–0.3. Fluctuations in the numbers of galaxies in these bins in terms of redshifts are caused by Poisson noise, correlated structures, and systematic errors in estimating photo-z. This method involves covering a sufficiently large region of the celestial sphere with a grid of deep multi-band surveys with a cell size on the order of 10o×10o, with deep fields of size ∼10'×10' observed with 3-10 meter telescopes at its nodes. The distribution of the photometric redshifts of the galaxies within each deep field will yield information on the radial extent of superlarge structures, while comparing the radial distributions in neighboring fields will yield information on the tangential extent of these structures. A necessary element of this method is an analysis of possible distortions in the radial distributions of the galaxies associated with the technique for evaluating the photometric redshifts.