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.     

Nearby galaxies. II. Luminosity function and spatial distribution

A sample of nearby galaxies (Schmidt and Boller 1992, paper I) has been analysed with regard to the luminosity function and the spatial distribution. The main results are as follows: (i) a relation between the slope of the luminosity function of the members of a group of galaxies and the earliest morphological type in this group has been detected which possibly is a new kind of environmental effects; (ii) the virial masses of the groups of galaxies are, on the average, by a factor 3 to 4 greater, only, than the luminous masses derived from the individual galaxy masses; (iii) the nearby galaxies are concentrated in a thin disk-like layer around the supergalactic plane the thickness of which is a few hundred kiloparsecs, only; (iv) a population of field galaxies with nearly constant density (about 3 per cent of the number density in the supergalactic plane) is extended into the voids on both the supergalactic hemispheres.     

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.     

The power spectrum of rich clusters of galaxies on large spatial scales

We present an analysis of the redshift-space power spectrum, P ( k ), of rich clusters of galaxies based on an automated cluster catalogue selected from the APM Galaxy Survey. We find that P ( k ) can be approximated by a power law, P ( k )∝ kⁿ , with n ≈−1.6 over the wavenumber range 0.04< k <0.1 h Mpc⁻¹. Over this range of wavenumbers, the APM cluster power spectrum has the same shape as the power spectra measured for optical and IRAS galaxies. This is consistent with a simple linear bias model in which different tracers have the same power spectrum as that of the mass distribution, but shifted in amplitude by a constant biasing factor. On larger scales, the power spectrum of APM clusters flattens and appears to turn over on a scale k ∼0.03 h Mpc⁻¹. We compare the power spectra estimated from simulated APM cluster catalogues with those estimated directly from cubical N -body simulation volumes, and find that the APM cluster survey should give reliable estimates of the true power spectrum at wavenumbers k ≳0.02 h Mpc⁻¹. These results suggest that the observed turnover in the power spectrum may be a real feature of the cluster distribution, and that we have detected the transition to a near-scale-invariant power spectrum implied by observations of anisotropies in the cosmic microwave background radiation. The scale of the turnover in the cluster power spectrum is in good agreement with the scale of the turnover observed in the power spectrum of APM galaxies.     

Cosmogony of galaxies as based on the spatial distribution of matter

A morphological box for the space distribution of galaxies and dark matter as the consequence of various types of cosmogonical hypotheses is presented. A short review of concepts of clustering of galaxies is given. One has to distinguish between the phenomena of “clusters of galaxies” and of “clustering of galaxies”. The second notion is more general. The investigations of KIANG , FLIN , and PEEBLES speak in favour of general clustering rather than overal existence of individual clusters. Individuals such as our Supergalaxy, Coma cluster etc. seem rather to be exceptional features.     

Wide triplets of galaxies: collapse on spatial scales of ∼1 Mpc

We study triple systems of galaxies with mean projected harmonic separation ≃0.6  h ⁻¹ Mpc     We call the systems 'wide triplets', in contrast to compact triplets with mean projected harmonic separation ≃0.04  h ⁻¹ Mpc, studied by Karachentsev et al. Data are taken for 108 wide triplets from a list compiled by Trofimov & Chernin; at least one-third of them are considered to be probably isolated physical systems. With typical crossing times of about the Hubble time, the wide triplets seem to be in a state of ongoing collapse. This is confirmed by a set of computer models which simulate well the observational characteristics of the ensemble of wide triplets. The simulations also give a statistical estimate of the total mass of a typical wide triplet: it proves to be ≃10¹³ M_⊙. This figure indicates that the dark matter mass is 15–30 times the mass of baryonic matter in the systems. The dynamics of wide triplets, as well as their dark matter content, provide new direct cosmological constraints by establishing that hierarchical evolution is occurring on a mass scale of ∼10¹³ M_⊙ and a spatial scale of ∼1 Mpc.     

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.     

Modelling evolution of stellar emission of galaxies for the nir surveys

Recent observational results in the near-IR on distant galaxies and interacting galaxies are clues for modelling evolution of galaxy counts and for testing theories of galaxy formation. Spectrophotometric models, developed in the ultraviolet and visible, were tools essential for such interpretations. So we hereafter present their extension to the near-infrared and preliminary results on radiogalaxies, starbursts and faint counts. The two fundamental objectives are to confirm a merging scenario and to determine the age of the first stellar generation.     

Clustering of galaxies in a hierarchical universe – III. Mock redshift surveys

This is the third paper in a series which combines N -body simulations and semi-analytic modelling to provide a fully spatially resolved simulation of the galaxy formation and clustering processes. Here we extract mock redshift surveys from our simulations: a cold dark matter model with either Ω₀=1 ( τ CDM) or Ω₀=0.3 and Λ=0.7 (ΛCDM). We compare the mock catalogues with the northern region (CfA2N) of the Center for Astrophysics (CfA) Redshift Surveys. We study the properties of galaxy groups and clusters identified using standard observational techniques, and also the relation of these groups to real virialized systems. Most features of CfA2N groups are reproduced quite well by both models with no obvious dependence on Ω₀. Redshift‐space correlations and pairwise velocities are also similar in the two cosmologies. The luminosity functions predicted by our galaxy formation models depend sensitively on the treatment of star formation and feedback. For the particular choices of Paper I they agree poorly with the CfA survey. To isolate the effect of this discrepancy on our mock redshift surveys, we modify galaxy luminosities in our simulations to reproduce the CfA luminosity function exactly. This adjustment improves agreement with the observed abundance of groups, which depends primarily on the galaxy luminosity density, but other statistics, connected more closely with the underlying mass distribution, remain unaffected. Regardless of the luminosity function adopted, modest differences with observation remain. These can be attributed to the presence of the 'Great Wall' in the CfA2N. It is unclear whether the greater coherence of the real structure is a result of cosmic variance, given the relatively small region studied, or reflects a physical deficiency of the models.     

Density distribution of matter on 75-Mpc scales derived by the POTENT method from the bulk motions of RFGC galaxies

The data on the peculiar velocities of 1493 RFGC flat spiral galaxies processed using the POTENT method allowed the density distribution of matter, including dark matter, on 75-Mpc scales to be reconstructed. Well-known attractors (the Great Attractor, the Perseus—Pisces and Coma superclusters) and voids are separated from the distribution. In general, the density distribution is close to that of IRAS galaxies, suggesting that the luminous-to-dark matter density ratio is constant. The masses of the main attractors were estimated.     

Application of a newN-body code to the encounters of galaxies and dissipationless formation of elliptical galaxies

A new code has been used to simulate the formation of elliptical galaxies via a dissipationless collapse by a numerical experiment. Preliminary results of numerical simulations are presented for initial 2T/|W| conditions ranging from 10^–2 to 10^–5. The importance of inhomogeneity in the initial density distribution and of merging is outlined.Paper presented at the 11th European Regional Astronomical Meetings of the IAU on New Windows to the Universe, held 3–8 July, 1989, Tenerife, Canary Islands, Spain.     

The universal rotation curve of spiral galaxies – II. The dark matter distribution out to the virial radius

In the current ΛCDM cosmological scenario, N -body simulations provide us with a universal mass profile, and consequently a universal equilibrium circular velocity of the virialized objects, as galaxies. In this paper we obtain, by combining kinematical data of their inner regions with global observational properties, the universal rotation curve of disc galaxies and the corresponding mass distribution out to their virial radius. This curve extends the results of Paper I, concerning the inner luminous regions of Sb–Im spirals, out to the edge of the galaxy haloes.     

Astrophysical statistics of compact galaxies near the galactic north pole. Part II. Blue galaxies in the tautenburg catalogue of compact galaxies

Aus dem Tautenburger Katalog von 745 kompakten Galaxien in 4 Feldern um M3 wurden blaue Objekte selektiert. Dies geschah mit Hilfe des Farbenindex U – B ≧ −0.40 mag und durch spektroskopische Inspektion auf Objektivprismen-aufnahmen. Es wurden 45 Objekte als blau oder als emissionsverdächtig befunden.     

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.