Searcharxiv⌕ Search

arXiv subjects

A. G. Doroshkevich

Publications and source records attributed to A. G. Doroshkevich.

At least 19 recordsLinked to original sources
arXiv2024

Observations of Galaxies at $z\gtrsim10$ Allow to Test Cosmological Models with Features in the Initial Power Spectrum

The initial power spectrum of density perturbations, generated during the inflationary epoch, is now constrained by observations on scales $λ>5$~Mpc and has a power-law form. The peculiarities of the inflationary process can lead to the appearance of non-power-law contributions to this spectrum, such as peaks. The exact size and shape of the peak cannot be predicted in advance. In this paper, we propose methods for searching for such peaks in the region of the spectrum with $λ<5$~Mpc. Perturbations on these scales enter the nonlinear stage at $z\gtrsim10$, which is now becoming accessible to observations. Our studies of numerical models of large-scale structure with peaks in the initial spectrum have shown that spectral features on scales with $λ>0.1$~Mpc manifest in the clustering of galaxies, as well as affect their mass function, sizes, and density. Studying these characteristics of distant galaxies will allow us to constrain cosmological models with peaks.

astro-ph.CO↗
arXiv2019

Prospects of observation of gravitationally lensed sources by space submillimeter telescopes

In the current paper we consider the prospects of observation of gravitationally lensed sources in far-infrared and submillimeter wavelength ranges by the future space telescopes equipped with actively cooled main mirrors. We consider the possibility of solving some of the important cosmological and astrophysical scientific tasks by observation of gravitationally lensed sources. The number counts of lensed sources for wavelengths from 70$μm$ up to 2000$μm$ were calculated. We discuss the distribution of lensed sources at different redshifts and magnification coefficients and also mass distribution of lenses. Model sky maps that illustrate the contribution of lensed sources were created.

astro-ph.GA↗
arXiv2017

Beyond the standard $Λ$CDM cosmology: the observed structure of DM halos and the shape of the power spectrum

Recent advances in observational astronomy allow to study various groups of Dark Matter (DM) dominated objects from the dwarf spheroidal (dSph) galaxies to clusters of galaxies that span the mass range from $10^{6} M_{\odot}$ to $10^{15} M_{\odot}$. To analyze data of this divers collection of objects we used a simple toy model of spherical DM halo formation that was initially proposed by Peebles. This model introduced the concept of the epoch or redshift of halo formation. Using this concept we analyzed selected sample of DM dominated objects and we have found empirical 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 result 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 differs from expectations of the standard $Λ$CDM cosmology and 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↗
arXiv2015

Review of scientific topics for Millimetron space observatory

This paper describes outstanding issues in astrophysics and cosmology that can be solved by astronomical observations in a broad spectral range from far infrared to millimeter wavelengths. The discussed problems related to the formation of stars and planets, galaxies and the interstellar medium, studies of black holes and the development of the cosmological model can be addressed by the planned space observatory Millimetron (the "Spectr-M" project) equipped with a cooled 10-m mirror. Millimetron can operate both as a single-dish telescope and as a part of a space-ground interferometer with very long baseline.

astro-ph.IM↗
arXiv2012

Effect of small scale density perturbations on the formation of dark matter halo profiles

With help of a set of toy N-body models of dark halo formation we study the impact of small scale initial perturbations on the inner density profiles of haloes. We find a significant flattening of the inner slope $α={d \log ρ\over d \log r}$ to $α=-0.5$ in some range of scales and amplitudes of the perturbations (while in the case of absence of these perturbations the NFW profile with $α=-1$ is reproduced). This effect may be responsible for the formation of cuspless galactic haloes.

astro-ph.CO↗
arXiv2012

A solution to the problems of cusps and rotation curves in dark matter halos in the cosmological standard model

We discuss various aspects of the inner structure formation in virialized dark matter (DM) halos that form as primordial density inhomogeneities evolve in the cosmological standard model. The main focus is on the study of central cusps/cores and of the profiles of DM halo rotation curves, problems that reveal disagreements among the theory, numerical simulations, and observations. A method that was developed by the authors to describe equilibrium DM systems is presented, which allows investigating these complex nonlinear structures analytically and relating density distribution profiles within a halo both to the parameters of the initial small-scale inhomogeneity field and to the nonlinear relaxation characteristics of gravitationally compressed matter. It is shown that cosmological random motions of matter `heat up' the DM particles in collapsing halos, suppressing cusp-like density profiles within developing halos, facilitating the formation of DM cores in galaxies, and providing an explanation for the difference between observed and simulated galactic rotation curves. The analytic conclusions obtained within this approach can be confirmed by the N-body model simulation once improved spatial resolution is achieved for central halo regions.

astro-ph.CO↗
arXiv2007

Statistical characteristics of the observed metal systems and problems of reionization

We analyze basic properties of about 200 metal systems observed in high resolution spectra of 9 quasars by Boksenberg, Sargent & Rauch (2003). The measured Doppler parameters for the hydrogen and carbon lines are found to be different by a factor $\sim\sqrt{m_C/ m_H}$ what indicates the domination of the thermal broadening and high degree of relaxation for majority of the observed metal systems. The analysis of the mean separation of the metal systems confirms that they can be located in regions with the typical proper size $R_{cl}\sim 0.1 - 0.25h^{-1}$ Mpc what corresponds to the typical sizes of protogalaxies with the baryonic masses $M_b\approx 10^9-10^{10}M_\odot$. The metal abundances observed at redshifts $z=3 - 6$ within both IGM and galaxies are found to be quite similar to each other what indicates the strong interaction of young galaxies with the IGM and the important role of dwarf satellites of host galaxies in such interaction. On the other hand, this metal abundance can be considered as the integral measure of nuclear reactions within any stars what in turn restricts the contribution of the stars to the creation of ionizing UV background. Available now estimates of these abundances demonstrate that attempts to explain the reionization of the Universe as a byproduct of the process of synthesis of metals only are problematic and a significant contribution of unobserved and/or non thermal UV sources seems to be required.

astro-ph↗
arXiv2007

Possible extensions of the standard cosmological model: anisotropy, rotation, and magnetic field

We show that the difference between the theoretically expected and measured by WMAP amplitude of the quadrupole fluctuations of CMB can be related to the impact of the anisotropic curvature of the homogeneous universe dominated by the dark energy. In such universe the matter expansion becomes practically isotropic just after the period of inflation and only at small redshifts the anisotropic expansion is generated again by the small curvature $Ω_K=1- Ω_m- Ω_Λ\leq 10^{-4}$. For such models the possible deviations from the parameters derived for the standard cosmological model are evidently negligible but the correlations of large scale perturbations and distortions of their Gaussianity are possible. Such models are also compatible with existence of a homogeneous magnetic field and matter rotation which contribute to the low $\ell$ anisotropy and can be considered as ``hidden parameters'' of the model. Their influence can be observed as, for example, special correlations of small scale fluctuations and the Faraday rotation of the CMB and radiation of the farthest quasars. However, both the magnetic field and matter rotation require also modifications of the simple models of isotropic inflation and they change the evolutionary history of the early Universe.

astro-ph↗
arXiv2006

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

Properties of $\sim$ 6 000 Ly-$α$ absorbers observed in 19 high resolution spectra of QSOs are investigated using the model of formation and evolution of DM structure elements based on the Zel'dovich theory. This model asserts that absorbers are formed in the course of both linear and nonlinear adiabatic or shock compression of dark matter (DM) and gaseous matter. It allows us to link the column density and overdensity of DM and gaseous components with the observed column density of neutral hydrogen, redshifts and Doppler parameters of absorbers and demonstrates that at high redshifts we observe a self similar period of structure evolution with the Gaussian initial perturbations. We show that the colder absorbers are associated with rapidly expanded regions of a galactic scale which represent large amplitude negative density perturbations. We extend and improve the method of measuring the power spectrum of initial perturbations proposed in Demiański & Doroshkevich (2003b). Our method links the observed separations and the DM column density of absorbers with the correlation function of the initial velocity field. We recover the cold dark matter (CDM) like power spectrum at scales 10> D > 0.15Mpc/h with a precision of ~15%. However at scales $\sim 3 - 150 h^{-1}$kpc the measured and CDM--like spectra are different. This result suggests a possible complex inflation with generation of excess power at small scales.

astro-ph↗
arXiv2005

Gauss--Legendre Sky Pixelization (GLESP) for CMB maps

A new scheme of sky pixelization is developed for CMB maps. The scheme is based on the Gauss--Legendre polynomials zeros and allows one to create strict orthogonal expansion of the map. A corresponding code has been implemented and comparison with other methods has been done.

astro-ph↗
arXiv2005

First Release of Gauss-Legendre Sky Pixelization (GLESP) software package for CMB analysis

We report the release of the Gauss--Legendre Sky Pixelization (GLESP) software package version 1.0. In this report we present the main features and functions for processing and manipulation of sky signals. Features for CMB polarization is underway and to be incorporated in a future release. Interested readers can visit http://www.glesp.nbi.dk (www.glesp.nbi.dk) and register for receiving the package.

astro-ph↗
arXiv2003

Cross-correlation of the CMB and foregrounds phases derived from the WMAP data

We present circular and linear cross-correlation tests and the "friend-of-friend" analysis for phases of the Internal Linear Combination Map (ILC) and the WMAP foregrounds for all K--W frequency bands at the range of multipoles $\ell\le100$. We compare also Tegmark, de Oliveira-Costa and Hamilton (2003) and Naselsky et al. (2003) cleaned maps with corresponding foregrounds. We have found significant deviations from the expected Poissonian statistics for all the cleaned maps and foregrounds. Our analysis shows that, for a low multipole range of the cleaned maps, power spectra contains some of the foregrounds residuals mainly from the W band.

astro-ph↗
arXiv2003

Phase cross-correlation of the WMAP ILC map and foregrounds

We present a circular cross-correlation tests for the phases of the Internal Linear Combination Map (ILC) and {\it WMAP}'s foregrounds for all K--W frequency bands at the range of multipoles $\ell\le 50$. We have found significant deviations from the expected Poissonian statistics for the ILC and the foregrounds phases. Our analysis shows that the low multipole range of the ILC power spectrum contains some of the foregrounds residues.

astro-ph↗
arXiv2003

Observational estimates of the initial power spectrum at small scale from Lyman-$α$ absorbers

We present a new method of measuring the power spectrum of initial perturbations to an unprecedently small scale of $\sim$ 10$h^{-1}$ kpc. We apply this method to a sample of 4500 Ly-$α$ absorbers and recover the cold dark matter (CDM) like power spectrum at scales $\geq 300h^{-1}$kpc with a precision of $\sim$ 10%. However at scales $\sim 10 - 300 h^{-1}$kpc the measured and CDM--like spectra are noticeable different. This result suggests a complex inflation with generation of excess power at small scales. The magnitude and reliability of these deviations depend also upon the possible incompleteness of our sample and poorly understood process of formation of weak absorbers. Confirmation of the CDM--like shape of the initial power spectrum or detection of its distortions at small scales are equally important for widely discussed problems of physics of the early Universe, galaxy formation, and reheating of the Universe. Our method links the observed mass function of absorbers with the correlation function of the initial velocity field and therefore it avoids the Nyquist restrictions limiting the investigations based on the smoothed flux or density fields. The physical model of absorbers adopted here asserts that they are formed in the course of both linear and nonlinear adiabatic or shock compression of dark matter (DM) and gaseous matter. At scales $\geq 1h^{-1}$Mpc all characteristics of the DM component and, in particular, their redshift distribution are found to be consistent with theoretical expectations for Gaussian initial perturbations with a CDM--like power spectrum.

astro-ph↗
arXiv2002

Ionization history of the cosmic plasma in the light of the recent CBI and future PLANCK data

The paper is devoted to the methods of determination of the cosmological parameters from recent CMB observations. We show that the more complex models of kinetics of recombination with a few "missing" parameters describing the recombination process provide better agreement between measured and expected characteristics of the CMB anisotropy. In particular, we consider the external sources of the Ly-{alpha} and Ly-{c} radiation and the model with the strong clustering of baryonic component. These factors can constrain the estimates of the cosmological parameters usually discussed. We demonstrate also that the measurements of polarization can improve these estimates and, for the precision expected for the PLANCK mission, allow to discriminate a wide class of models.

astro-ph↗
arXiv2002

Ionization history of the Universe as a test for Super Heavy Dark Matter particles

In this paper we discuss the possible distortions of the ionization history of the universe caused by an injection of non-thermal energy due to decays of hypothetical Super Heavy Dark Matter (SHDM) particles. These particles are usually considered as a possible source of Ultra High Energy Cosmic Rays (UHECRs) in the framework of the Top-Down model. Estimates of fraction of energy of decays converted to the UV range show that, for suitable parameters of SHDM particles, the significant distortions of power spectra of CMB anisotropy appear. Comparison with the observed power spectrum allows to restrict some properties of the SHDM particles. These decays can also increase of about 5 -- 10 times the degree of ionization of hydrogen at redshifts $z\sim$ 10 -- 50 that essentially accelerates the formation of molecules $H_2$ and first stars during "dark ages".

astro-ph↗
arXiv2000

Ultra - High Energy Cosmic Rays from decay of the Super Heavy Dark Matter Relics

In this paper we briefly discuss the problem of the origin of Ultra High Energy Cosmic Rays in the framework of Top-Down models. We show that, for high energy of decays and in a wide range of spectra of injected protons, their extragalactic flux is consistent with the observed fluxes of cosmic rays in the energy range 0.1 E_{GZK}< E < 10E_{GZK}. For suitable energy and spectra of injected protons, the contribution of galactic sources is moderate, in this energy range, but it dominates at smaller and larger energies. In such models we can expect that at these energies the anisotropy of cosmic rays distribution over sky will be especially small. Some possible manifestations of decays of super massive particles such as, for example, primordial black holes with masses M_{pbh} ~ 10^{-5} g, are considered. In particular, we show that partial conversion of energy released during these decays at redshifts z ~ 1000 to Ly-alpha photons can delay the hydrogen recombination and distort the spectrum of fluctuations of the cosmic microwave background radiation.

astro-ph↗