The method of a two-point conditional column density for estimating the fractal dimension of the distribution of galaxies

We suggest a new method for estimating the fractal dimension of the spatial distribution of galaxies: the method of selected cylinders. We show the capabilities of this method by constructing a two-point conditional column density for galaxies with known redshifts from the LEDA database. The fractal dimension of a sample of LEDA and EDR SDSS galaxies has been estimated to be 2.1±0.1 for cylinder lengths of 200 Mpc. A major advantage of the suggested method is that it allows scales comparable to the catalog depth to be analyzed for galaxy surveys in the form of conical sectors and small fields in the sky.     

Galaxy redshift abundance periodicity from Fourier analysis of number counts N(z) using SDSS and 2dF GRS galaxy surveys

A Fourier analysis on galaxy number counts from redshift data of both the Sloan Digital Sky Survey and the 2dF Galaxy Redshift Survey indicates that galaxies have preferred periodic redshift spacings of Δz= 0.0102, 0.0246, and 0.0448 in the SDSS and strong agreement with the results from the 2dF GRS. The redshift spacings are confirmed by the mass density fluctuations, the power spectrum P(z) and N _pairs calculations. Application of the Hubble law results in galaxies preferentially located on co-moving concentric shells with periodic spacings. The combined results from both surveys indicate regular co-moving radial distance spacings of 31.7±1.8 h^?1?Mpc, 73.4±5.8 h^?1?Mpc and 127±21 h^?1? Mpc. The results are consistent with oscillations in the expansion rate of the universe over past epochs.     

Comparison of Velocity Fields of the Galaxies From the Catalogs RFGC and MarkIII

A distribution of matter up to 100 h ^-1 Mpc could be obtained from the large-scale galaxy peculiar motions. The best picture of such motion is given for today by two galaxy catalogs, namely MarkIII and RFGC. We compare their velocity fields and show they are very similar and have not only practically the same multipole structure but also a corresponding small-scale motions . We estimate a mean radial component of this small-scale motion as 500–700 kms. An additional comparison of distances to common galaxies is made. This revised version was published online in July 2006 with corrections to the Cover Date.     

Properties of voids in the 2dFGRS galaxy survey

A method for detecting voids in the galaxy distribution is presented. Using this method, we have identified 732 voids with a radius of the seed sphere R _seed > 4.0h ^?1 Mpc in a volume-limited sample of galaxies from the southern part of the 2dFGRS survey. 110 voids with R _seed > 9.0h ^?1 Mpc have a positive significance. The mean volume of such voids is ～19 × 10³ h ^?3 Mpc³. Voids with R _seed > 9.0h ^?1 Mpc occupy 55% of the sample volume. We construct a dependence of the volumes of all the identified voids on their ranks and determine parameters of the galaxy distribution. The dependence of the volume of voids on their rank is consistent with a fractal model (Zipf’s power law) of the galaxy distribution with a fractal dimension D ≈ 2.1 (given the uncertainty in determining the dimension using our method and the results of a correlation analysis) up to scales of ～25h ^?1 Mpc with the subsequent transition to homogeneity. The directions of the greatest elongations of voids and their ellipticities (oblateness) are determined from the parameters of equivalent ellipsoids. The directions of the greatest void elongations have an enhanced concentration to the directions perpendicular to the line of sight.     

Global structure of the local universe according to 2MRS survey

We report the results of a statistical analysis of the space distribution of galaxies of the 2MRS catalog, which contains redshifts of 43533 galaxies of the 2MASS all-sky IR survey. Because of the unique features of the 2MRS survey, such as its 90% sky coverage, galaxy selection in the IR, the complete incorporation of the old stellar population of galaxies, weakness of the dust extinction effects, and the smallness of the k- and e-corrections allowed us to determine the statistical properties of the global distribution of galaxies in the Local Universe. We took into account the main methodological factors that distort the theoretically expected relations compared to those actually observed. We construct the radial galaxy number counts N(R), SL(R, r) statistics, and the complete correlation function (conditional density) Γ(r) for volume-limited (VL) galaxy samples. The observed conditional density Γ(r) in the redshift space is independent of the luminosity of galaxies and has the form of a power-law function with exponent γ ≈ 1.0 over a large range scale-length spanning from 0.1 to 100 Mpc. We compare the statistical properties of the space distribution of galaxies of the 2MRS catalog with the corresponding properties of simulated catalogs: stochastic fractal distributions and galaxies of the Millennium catalog.     

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.     

Method for analyzing the spatial distribution of galaxies on gigaparsec scales. I. initial principles

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.     

由SLOAN观测数据测试大尺度结构的均匀性

宇宙学的基本假设之一是宇宙在大尺度上均匀各向同性.为了验证星系分布在大尺度上的均匀性,分别计算观测样本和观测空间几何体的分形维数,得到SDSS-DR4中星系分布的分形维数.观测空间几何体的分形维数用随机样本来确定.样本中的星系红移z的范围为0.01-0.26.当尺度持续增加至几十个Mpc时,星系分布的分形维数一致地趋向于3.所有的样本均显示了明显的转变尺度,当尺度大于此转变尺度时,星系分布的分形维数D<,G>～3,星系的分布转变为均匀分布.结果支持了宇宙学的基本原理关于宇宙大尺度均匀的假设.样本的转变尺度随着样本的光度增强而变大,说明小尺度上星系的分布不是简单的分形分布,而是多维分形分布.高光度星系的转变尺度非常大,直到100h-1Mpc左右才变得均匀.     

Classical cosmological tests for galaxies of the Hubble Ultra Deep Field

Images of the Hubble Ultra Deep Field are analyzed to obtain a catalog of galaxies for which the angular sizes, surface brightness, photometric redshifts, and absolute magnitudes are found. The catalog contains a total of about 4000 galaxies identified at a high signal-to-noise ratio, which allows the cosmological relations angular size—redshift and surface brightness-redshift to be analyzed. The parameters of the evolution of linear sizes and surface brightness of distant galaxies in the redshift interval 0.5–6.5 are estimated in terms of a grid of cosmological models with different density parameters (Ω _V ; Ω _m ). The distribution of photometric redshifts of galaxies is analyzed and possible superlarge inhomogeneities in the radial distribution of galaxies are found with scale lengths as large as 2000 Mpc.     

Testing the Homogeneity of Large-scale Structure with the SDSS Data

One of the basic assumptions in cosmology is that the universe is homogeneous and isotropic on large scales. This assumption is the most important keystone of modern cosmology. In order to verify the homogeneity of galaxy distribution on large scales, we have computed the fractal dimensionality of the galaxy distribution in SDSS-DR4. The fractal dimensionality of the observed spatial geometric bodies is determined with random samples. The redshifts of sample galaxies are in the range 0.01～0.26. When the scale grows continuously to dozens of Mpc, the fractal dimensionality of the galaxy distribution approaches to 3 consistently. All the 6 samples exhibit obviously a transition scale. For scales larger than the transition scale, the fractal dimensionality D_G of the galaxy distribution is very close to 3, the galaxy distribution is homogeneous. This result supports the assumption that the universe is homogeneous on large scales. The transition scale of the sample increases with the luminosity of the sample. This means that the galaxy distribution on small scales is not a of simple fractal distribution, but a multi-fractal distribution. The transition scale of high-luminosity galaxies is very large, the distribution will not become homogeneous till about 100 h^?1Mpc.     

Approaching a homogeneous galaxy distribution: results from the Stromlo–APM redshift survey

Recent results from a number of redshift surveys suggest that the Universe is well described by an inhomogeneous, fractal distribution on the largest scales probed. This distribution has been found to have fractal dimension, D , approximately equal to 2.1, in contrast to a homogeneous distribution in which the dimension should approach the value 3 as the scale is increased. In this paper we demonstrate that estimates of D , based on the conditional density of galaxies, are prone to bias from several sources. These biases generally result in a smaller measured fractal dimension than the true dimension of the sample. We illustrate this behaviour in application to the Stromlo–APM redshift survey, showing that this data set in fact provides evidence for fractal dimension increasing with survey depth. On the largest scale probed, r ≈60  h ⁻¹ Mpc, we find evidence for a distribution with dimension D =2.76±0.10. A comparison between this sample and mock Stromlo–APM catalogues taken from N -body simulations (which assume a CDM cosmology) reveals a striking similarity in the behaviour of the fractal dimension. Thus we find no evidence for inhomogeneity in excess of that expected from conventional cosmological theory. We consider biases affecting future large surveys and demonstrate, using mock SDSS catalogues, that this survey will be able to measure the fractal dimension on scales at which we expect to see full turn-over to homogeneity, in an accurate and unbiased way.     

Radio sources in the 2dF Galaxy Redshift Survey – II. Local radio luminosity functions for AGN and star-forming galaxies at 1.4 GHz

We have cross-matched the 1.4-GHz NRAO VLA Sky Survey (NVSS) with the first 210 fields observed in the 2dF Galaxy Redshift Survey (2dFGRS), covering an effective area of 325 deg² (about 20 per cent of the final 2dFGRS area). This yields a set of optical spectra of 912 candidate NVSS counterparts, of which we identify 757 as genuine radio identifications – the largest and most homogeneous set of radio source spectra ever obtained. The 2dFGRS radio sources span the redshift range     to 0.438, and are a mixture of active galaxies (60 per cent) and star-forming galaxies (40 per cent). About 25 per cent of the 2dFGRS radio sources are spatially resolved by NVSS, and the sample includes three giant radio galaxies with projected linear size greater than 1 Mpc. The high quality of the 2dF spectra means we can usually distinguish unambiguously between AGN and star-forming galaxies. We make a new determination of the local radio luminosity function at 1.4 GHz for both active and star-forming galaxies, and derive a local star formation density of         .     

The topology of the 2-degree field galaxy redshift survey

We analyse the topology of density surfaces drawn from the recently completed southern galactic strip (SGP) of the 2-degree field galaxy redshift survey (2dFGRS). We calculate the genus curves of the smoothed density fields drawn from the 2dFGRS SGP on scales ranging from 5h^-1 Mpc to 50h^-1 Mpc and compare them with the genus curves of the density fields with the same power spectrum but random phases, therefore measuring the level of phase correlation present in 2dF. We find that on scales larger than 15h^-1 Mpc the measured genus curves of 2dF are very close to those expected for gaussian random fields. Below this scale, however, we can observe non-gaussianity which we believe originates from non-linear gravitational evolution. The unprecedented number of resolution elements in 2dF allows us to measure non-gaussianity with great accuracy.     

Edge-on Galaxies in the Hubble Ultra Deep Field

We have produced a sample of 58 edge-on spiral galaxies at redshifts z ~ 1 selected in the Hubble Ultra Deep Field. For all galaxies we have analyzed the 2D brightness distributions in the V₆₀₆ and i₇₇₅ filters and measured the radial (h_r) and vertical (h_z) exponential scale lengths of the brightness distribution. We have obtained evidence that the relative thickness of the disks of distant galaxies, i.e., the ratio of the vertical and radial scale lengths, on average, exceeds the relative thickness of the disks of nearby spiral galaxies. The vertical scale length h_z of the stellar disks of galaxies shows no big changes at z = 1. The possibility of the evolution of the radial scale length h_z for the brightness distribution with redshift is discussed.

     

Surveying the Local Supercluster Plane

We investigate the distribution and velocity field of galaxies situated in a band of 100 by 20 degrees centered on M87 and oriented along the Local supercluster plane. Our sample amounts 2158 galaxies with radial velocities less than 2000 km s^?1. Of them, 1119 galaxies (52%) have distance and peculiar velocity estimates. About 3/4 of early-type galaxies are concentrated within the Virgo cluster core, most of the late-type galaxies in the band locate outside the virial radius. Distribution of gas-rich dwarfs with M_HI >M_* looks to be insensitive to the Virgo cluster presence. Among 50 galaxy groups in the equatorial supercluster band 6 groups have peculiar velocities about 500–1000 km s^?1 comparable with virial motions in rich clusters. The most cryptic case is a flock of nearly 30 galaxies around NGC4278 (Coma I cloud), moving to us with the mean peculiar velocity of ?840 km s^?1. This cloud (or filament?) resides at a distance of 16.1 Mpc from us and approximately 5 Mpc away from the Virgo center. Galaxies around Virgo cluster exhibit Virgocentric infall with an amplitude of about 500 km s^?1. Assuming the spherically symmetric radial infall, we estimate the radius of the zero-velocity surface to be R₀ = (7.0±0.3) Mpc that yields the total mass of Virgo cluster to be (7.4 ± 0.9)× 10¹⁴M_⊙ in tight agreement with its virial mass estimates. We conclude that the Virgo outskirts does not contain significant amounts of dark mater beyond its virial core.     

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.     

266 E+A galaxies selected from the Sloan Digital Sky Survey Data Release 2: the origin of E+A galaxies

E+A galaxies are characterized as galaxies with strong Balmer absorption lines but without any [O  ii ] or Hα emission lines. The existence of strong Balmer absorption lines indicates that E+A galaxies have experienced starburst within the past one gigayear. However, the lack of [O  ii ] and Hα emission lines indicates that E+A galaxies do not have any on-going star formation. Therefore, E+A galaxies are interpreted as post-starburst galaxies. For many years, however, it has been a mystery why E+A galaxies started starburst and why they quenched star formation abruptly. Using one of the largest samples of 266 E+A galaxies carefully selected from the Sloan Digital Sky Survey Data Release 2, we have investigated the environment of E+A galaxies from 50 kpc to 8 Mpc scale, i.e. from a typical distance to satellite galaxies to the scale of large-scale structures. We found that E+A galaxies have an excess of local galaxy density only at a scale of <100 kpc (with a 2σ significance), but not at the cluster scale (∼1.5 Mpc) nor at the scale of large-scale structure (∼8 Mpc). These results indicate that E+A galaxies are not created by the physical mechanisms associated with galaxy clusters or the large-scale structure, but are likely to be created by dynamical interaction with closely accompanying galaxies at a <100 kpc scale. The claim is also supported by the morphology of E+A galaxies. We have found that almost all E+A galaxies have a bright compact core, and that ∼30 per cent of E+A galaxies have dynamically disturbed signatures or tidal tails, which quite strongly suggest the morphological appearance of merger/interaction remnants.     

从准一维红移巡天样本分析大尺度结构

通过分析由五个笔形天区的完备红移巡天和九个1/3采样红移巡天得到的样本,研究了星系分布中的大尺度结构。用一种改进过的方法计算了该分布的分维。结果表明星系分布确实具有3—4.5h~(-1)Mpc的典型尺度,这与Shanks等的结果一致。     

Structures in the large-scale distribution of galaxies with different luminosities

The large-scale structures of volume-limites subsample sorted out from the CfA catalog have been analysed by percolation method. The result shows that the features in the distribution of galaxies with different luminosities are significantly different. Especially, the most luminous galaxies are likely to exhibit hierarchical clustering on a scale about 50h ₅₀ ^–1 Mpc, and the least luminous galaxies in our subsamples show string-like or sheet-like character in their distribution. These results suggest that the large-scale distribution of galaxies consists of clusters or cluster cores of most luminous galaxies and the less luminous galaxies spread out from these cores with a string-like or sheet-like structure. This picture of the large-scale distribution consists with previous results from two-point correlation analysis and fractal analysis. The implication of these results has been discussed.