arXiv subjects

A. Doroshkevich

Publications and source records attributed to A. Doroshkevich.

15 recordsLinked to original sources

arXiv2024

Formation of the first halos, galaxies and magnetic fields

Cosmic objects with magnetic fields (quasars, radiogalaxies) are observed at redshifts $z\geq 7$ (Wang et al., 2021, Fan et al., 2023, Yang et al., 2024) and more (for instance, for $z = 10.073\pm 0.002$, Goulding et al., 2023) indicates the early creation of magnetic fields. The observations of the cosmic telescope JWST show that the first galaxies were formed at redshifts $z\simeq$ 15 -- 20. We link the transformation of the low mass dark matter halos into galaxies with the creation of the first stars owing to the radiative cooling of partly ionized hydrogen at $z\geq 10$. The early formation of galaxies creates favourable conditions for high impact of the Compton scattering of the relic radiation photons and electrons on the electron temperature and leads to the partial separation of electrons and protons. Together with turbulent motions such separation stimulates creation of magnetic fields on a galactic scale. The same processes distort the primordial perturbations of the relic radiation what can be observed and confirmed in special simulations.

astro-ph.CO↗

arXiv2020

The patch like model of galaxies formation: the virial paradox, core-cusp and missing satellite problems

The patch like model of the hierarchical galaxy formation in the $Λ$CDM cosmological model with small damping scale is considered. In this model galaxies and clusters of galaxies are identified with rare high density peaks, what suppresses the action of random factors in the vicinity of peaks and makes the process of halos formation more rapid and regular. High concentration of irregular subhalos surrounding the central peaks and their subsequent merging just after formation allows to consider this medium as a mixture of collisionless dispersed dark matter (DM) particles and collisional subhalos. Merging of these subhalos with the central dominating halo is accompanied by tidal destruction of the central cusp, what progressively shallows the density profile and promotes formation of super massive central black holes. In the framework of this model we can reproduce the observed correlation of mass and density of virialized galaxies and clusters of galaxies known as the virial paradox [4,5]. These correlations are closely linked with the composition of DM and the shape of the power spectrum what allows to restrict them using already available observations. These correlations put constraints on the HDM and WDM models and allow to test models of cosmological inflation. We confirm that the missing satellite problem is directly linked with the virial paradox and reheating of the Universe which increases temperature and entropy of the baryons, prevents formation of first stars and divides halos into two populations: the first one includes galaxies formed before reheating which are mainly concentrated in the vicinity of the massive ones while the second population -- numerous dark halos formed after reheating -- accumulates majority of DM but does not contain stars. Their spatial distribution is more homogeneous.

astro-ph.CO↗

arXiv2017

Self similarity of the dark matter dominated objects and the shape of small scale power spectrum

We analyzed available observational data of a sample of dark matter (DM) dominated galaxies and clusters of galaxies and we have found correlations between the virial mass, $M_{vir}$, of halos and basic parameters of their cores, namely, the mean DM density, pressure and entropy. These correlations are a natural consequence of similar evolution of all such objects. It is driven mainly by gravitational interactions what implies a high degree of self similarity of both the process of halos formation and their internal structure. We confirmed the CDM--like shape of both the small and large scale power spectrum. However, our reconstruction of the evolutionary history of observed objects requires either a multicomponent composition of DM or a more complex primordial power spectrum of density perturbations with significant excess of power at scales of clusters of galaxies and larger. We demonstrated that a model with suitable combination of the heavy DM particles (CDM) and DM particles with large damping scale (HDM) could provide a successful description of the observational data in a wide range of masses.

astro-ph.CO↗

arXiv2014

Beyond the $Λ$CDM cosmology: complex composition of dark matter

The mass and composition of dark matter (DM) particles and the shape and damping scales of the power spectrum of density perturbations can be estimated from recent observations of the DM dominated relaxed objects -- dwarf galaxies and clusters of galaxies. We confirm that the observed velocity dispersion of dSph galaxies agrees with the possible existence of DM particles with mass $m_w\sim 15 - 20keV$. More complex analysis utilizes the well known semi analytical model of formation of DM halos in order to describe the basic properties of corresponding objects and to estimate their redshifts of formation. For the DM halos this redshift is determined by their masses and the initial power spectrum of density perturbations. This correlation allows us to partly reconstruct the small scale spectrum of perturbations. We consider the available sample of suitable observed objects that includes $\sim 40$ DM dominated galaxies and $\sim 40$ clusters of galaxies and we show that the observed characteristics of these objects are inconsistent with expectations of the standard $Λ$CDM cosmological model. However, they are consistent with a more complex DM model with a significant contribution of the hot DM--like power spectrum with relatively large damping scale ($\sim 10 - 30Mpc$). The HDM component of DM decelerates but does not prevent formation of low mass objects. These preliminary inferences require confirmation by a more representative observational data that should include -- if possible -- DM dominated objects with intermediate masses $M\sim 10^{10} - 10^{12} M_\odot$. Comparison of observed properties of such objects with numerical simulations will provide more detailed picture of the process of formation of DM halos.

astro-ph.CO↗

arXiv2011

Simulated evolution of the dark matter large-scale structure

We analyze evolution of the basic properties of simulated large scale structure elements formed by dark matter (DM LSS) and confront it with the observed evolution of the Lyman-$α$ forest. In three high resolution simulations we selected samples of compact DM clouds of moderate overdensity. Clouds are selected at redshifts $0\leq z\leq 3$ with the Minimal Spanning Tree (MST) technique. The main properties of so selected clouds are analyzed in 3D space and with the core sampling approach, what allows us to compare estimates of the DM LSS evolution obtained with two different techniques and to clarify some important aspects of the LSS evolution. In both cases we find that regular redshift variations of the mean characteristics of the DM LSS are accompanied only by small variations of their PDFs, what indicates the self similar character of the DM LSS evolution. The high degree of relaxation of DM particles compressed within the LSS is found along the shortest principal axis of clouds. We see that the internal structure of selected clouds depends upon the mass resolution and scale of perturbations achieved in simulations. It is found that the low mass tail of the PDFs of the LSS characteristics depends upon the procedure of clouds selection.

astro-ph.CO↗

arXiv2010

CMB component separation in the pixel domain

We show that the popular ILC approach is unstable in respect to the division of the sample of map pixels to the set of ``homogeneous'' subsamples. For suitable choice of such subsamples we can obtain the restored CMB signal with amplitudes ranged from zero to the amplitudes of the observed signal. We propose approach which allows us to obtain reasonable estimates of $C_\ell$ at $\ell\leq 30$ and similar to WMAP $C_\ell$ for larger $\ell$. With this approach we reduce some anomalies of the WMAP results. In particular, our estimate of the quadrupole is well consistent to theoretical one, the effect of the ``axis of evil'' is suppressed and the symmetry of the north and south galactic hemispheres increases. This results can change estimates of quadrupole polarization and the redshift of reionization of the Universe. We propose also new simple approach which can improve WMAP estimates of high $\ell$ power spectrum.

astro-ph.CO↗

arXiv2007

A solution of the cusp problem in relaxed halos of dark matter

We propose a solution of the cusp problem in framework of the standard $Λ$CDM cosmology. To do this we describe the linear and nonlinear periods of halo formation by the entropy function of dark matter particles. This approach allows us to take into account together the impact of both the processes of nonlinear relaxation of compressed matter and the small scale initial velocity perturbations in collapsed halos. We show that such random velocities lead to the random variations of the density profile of relaxed halos. As a rule, they suppress the formation of cusp--like halos and favor the creation of core--like ones. This approach allows us to reproduce observed rotation curves, to explain their random scatter and deviations from simulated ones.

astro-ph↗

arXiv2002

Statistical characteristics of observed Ly-$α$ forest and the shape of initial power spectrum

Properties of $\sim$ 5000 observed Ly-$α$ absorbers are investigated using the model of formation and evolution of DM structure elements based on the Zel'dovich theory. This model is generally consistent with simulations of absorbers formation, accurately describes the Large Scale Structure observed in the galaxy distribution at small redshifts and emphasizes the generic similarity of the LSS and absorbers. The simple physical model of absorbers asserts that they are composed of DM and gaseous matter and it allows us to estimate the column density and overdensity of DM and gaseous components and the entropy of the gas trapped within the DM potential wells. The parameters of DM component are found to be consistent with theoretical expectations for the Gaussian initial perturbations with the WDM--like power spectrum. We demonstrate the influence of the main physical factors responsible for the absorbers evolution. The analysis of redshift distribution of absorbers confirms the self consistence of the assumed physical model and allows to estimate the shape of the initial power spectrum at small scales what in turn restricts the mass of dominant fraction of DM particles to $M_{DM}\approx 0.6 - 2$ keV. Our results verify the redshift variations of intensity of the UV background by about $4 - 6$ times and indicate that, perhaps, the available observations underestimate the intensity of this background.

astro-ph↗

arXiv2002

Large Scale Structure in the SDSS Galaxy Survey

The Large Scale Structure (LSS) in the galaxy distribution is investigated using the Sloan Digital Sky Survey Early Data Release (SDSS EDR). Using the Minimal Spanning Tree technique we have extracted sets of filaments, of wall-like structures, of galaxy groups, and of rich clusters from this unique sample. The physical properties of these structures were then measured and compared with the expectations from Zel'dovich' theory. The measured characteristics of galaxy walls were found to be consistent with those for a spatially flat $Λ$CDM cosmological model with $Ω_m\approx$ 0.3 and $Ω_Λ\approx$ 0.7, and for Gaussian initial perturbations with a Harrison -- Zel'dovich power spectrum. Furthermore, we found that the mass functions of groups and of unrelaxed structure elements generally fit well with the expectations from Zel'dovich' theory, although there was some discrepancy for lower mass groups which may be due to incompleteness in the selected sample of groups. We also note that both groups and rich clusters tend to prefer the environments of walls, which tend to be of higher density, rather than the environments of filaments, which tend to be of lower density. Finally, we note evidence of systematic differences in the properties of the LSS between the Northern Galactic Cap stripe and the Southern Galactic Cap stripe -- in particular, in the physical properties of the walls, their spatial distribution, and the relative numbers of clusters embedded in walls. Because the mean separation of walls is $\approx$ 60 -- 70$h^{-1}$ Mpc, each stripe only intersects a few tens of walls. Thus, small number statistics and cosmic variance are the likely drivers of these systematic differences.

astro-ph↗

arXiv2001

Negative intensity patches in angular variations of CMB as a probe of the period of reionization

The observational tests for the period of reionization of the universe are discussed. We show that this period can be observed as {\it negative} intensity patches of the CMB radiation with the amplitude $δT/T\sim 10^{-5}$ and the angular sizes $θ_T\sim$10 angular seconds in range of the wavelength 0.1 cm$\leqλ\leq$1 cm. The expected number density and frequency dependence of the amplitude permit to recognize this effect and to discriminate it from the noise. This method applied to the small scale variations of CMB temperature complements well the traditional spectral approach. The number density and the amplitude of observed 'negative' intensity patches depend upon the redshift of reionization that allow to estimate roughly this redshift. The ionized bubbles formed just before the period of reionization could also be seen as the highest peaks. The expected results are sensitive to the Jeans scale at the period of reionization, to the small scale shape of the primordial power spectrum and to the mass of dark matter particles.

astro-ph↗

arXiv2000

Properties of observed Ly-$α$ forest

The main observed properties of Ly-$α$ absorbers are investigated on the basis of theoretical model of formation and evolution of DM structure elements. This model is generally consistent with simulations of absorbers formation and with statistical description of structure evolution based on the Zel'dovich theory. The analysis of redshift variations of comoving linear number density of absorbers was performed in our previous paper. We show that the observed characteristics of Doppler parameter can be related to the size of DM structure elements what allows us to explain the observed distribution of Doppler parameter. This distribution is found to be consistent with the Gaussian initial perturbations. The observed characteristics of entropy and column density, $N_{HI}$, confirm that merging of pancakes is the main evolutionary process at redshifts $z\geq 2$. The observed sample of absorbers characterizes mainly the matter distribution within large low density regions and therefore it is difficult to reconstruct the density field from the distribution of absorbers.

astro-ph↗

arXiv1999

Statistical characteristics of formation and evolution of structure in the universe

An approximate statistical description of the formation and evolution of structure of the universe based on the Zel'dovich theory of gravitational instability is proposed. It is found that the evolution of DM structure shows features of self-similarity and the main structure characteristics can be expressed through the parameters of initial power spectrum and cosmological model. For the CDM-like power spectrum and suitable parameters of the cosmological model the effective matter compression reaches the observed scales $R_{wall}\sim $20 -- 25$h^{-1}$Mpc with the typical mean separation of wall-like elements $D_{SLSS}\sim $50 -- 70$h^{-1}$Mpc. This description can be directly applied to the deep pencil beam galactic surveys and absorption spectra of quasars. For larger 3D catalogs and simulations it can be applied to results obtained with the core-sampling analysis. It is shown that the interaction of large and small scale perturbations modulates the creation rate of early Zel'dovich pancakes and generates bias on the SLSS scale. For suitable parameters of the cosmological model and reheating process this bias can essentially improve the characteristics of simulated structure of the universe. The models with $0.3\leq Ω_m \leq 0.5$ give the best description of the observed structure parameters. The influence of low mass "warm" dark matter particles, such as a massive neutrino, will extend the acceptable range of $Ω_m$ and $h$.

astro-ph↗

arXiv1999

Geometry and Statistics of Cosmic Microwave Polarization

Geometrical and statistical properties of polarization of CMB are analyzed. Singular points of the vector field which describes CMB polarization are found and classified. Statistical distribution of the singularities is studied. A possible signature of tensor perturbations in CMB polarization is discussed. For a further analysis of CMB statistics Minkowski functionals are used, which present a technically simple method to search for deviations from a Gaussian distribution.

astro-ph↗

arXiv1995

Correlation function as a measure of the structure

Geometrical model of structure of the universe is examined to obtain analytical expression for the two points nonlinear correlation function. According to the model the objects (galaxies) are concentrated into two types of structure elements - filaments and sheets. We considered the filaments ( similar to galaxy filaments ) simply as straight lines and the sheets ( similar to superclusters of galaxies ) simply as planes. The homogeneously distributed objects are also taken into consideration. The spatial distribution of lines, planes and points is uncorrelated. The nonlinear correlation function depends on four parameters and is similar to the observed and simulated ones for different samples. It describes quite well the correlation of galaxies, clusters of galaxies and dark matter distribution. Possible interpretation of the parameters of nonlinear correlation function is discussed.

astro-ph↗

arXiv1995

The formation and evolution of large- and superlarge-scale structure in the universe -I: General Theory

A quantitative theory, based on the Zeldovich approximation, to provide an approximate description of the evolution of structure is presented. We give an expression for the characteristic scale of superlarge-scale structure which can also be applied to power spectra with a Harrison-Zeldovich asymptotic. The evolution of the characteristic scale of large-scale structure is described with an analytical expression. It corresponds to the mean separation of filaments or chains of galaxies. We apply the theory to some simulations and show that the theoretically defined characteristic scale for LSS does also correspond to the 'physical measurement' of the mean separation of dark matter LSS elements. This supports our claim for a new theory for the quantitative description of the formation and evolution of large-scale structure in the universe.

astro-ph↗