arXiv subjects

B. Novosyadlyj

Publications and source records attributed to B. Novosyadlyj.

42 records · Page 3Linked to original sources

arXiv1999

Evolution of a correlation function of QSOs and the initial power spectrum of density fluctuations

The evolution of two-point space correlation function of QSOs is analyzed in the framework of the theory of the large scale structure formation. For given cosmological models the agreement between theoretical predictions and observational data on correlation function of QSOs is achieved by determination of scales of structures R(z), in which could be formed quasars at different redshifts z. It is shown that quasars could be formed in the nucleus of massive galaxies or groups of galaxies owing to merges at their central region. It depends on an amplitude of the power spectrum of the initial matter density fluctuations at galaxy-cluster scales.

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arXiv1999

Best-fit parameters of MDM model from Abell-ACO power spectra and mass function

The possibility of determining MDM model parameters on the basis of observable data on the Abell-ACO power spectrum and mass function is analysed. It is shown that spectrum area corresponding to these data is sensitive enough to such MDM model parameters as neutrino mass $m_ν$, number species of massive neutrino $N_ν$, baryon content $Ω_b$ and Hubble constant $h\equiv H_0/100km/s/Mpc$. The $χ^2$ minimization method was used for their determination. If all these parameters are under searching then observable data on the Abell-ACO power spectrum and mass function prefer models which have parameters in the range $Ω_ν$ ($\sim 0.4-0.5$), low $Ω_b$ ($\le 0.01$) and $h$ ($\sim 0.4-0.6$). The best-fit parameters are as follows: $N_ν=3$, $m_ν=4.4eV$, $h=0.56$, $Ω_b\le 0.01$. The high-$Ω_b\sim 0.4-0.5$ solutions are obtained when mass of neutrino is fixed and $\le 3eV$. To explain the observable excessive power at $k\approx 0.05h/Mpc$ the peak of Gaussian form was introduced in primordial power spectrum. Its parameters (amplitude, position and width) were determined along with the MDM model parameters. It decreases $χ^2$, increases the bulk motions, but does not change essentially the best-fit MDM parameters. It is shown also that models with the median $Ω_ν\sim 0.2-0.3$ ($m_ν\sim 2.5$, $N_ν\sim 2-3$) and $Ω_b=0.024/h^2$, which match constraints arising from cosmological nucleosynthesis and high redshift objects, are not ruled out by these data ($Δχ^2<1$).

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arXiv1999

An analytic approximation of MDM power spectra in four dimensional parameter space

An accurate analytic approximation of the transfer function for the power spectra of primordial density perturbations in mixed dark matter models is presented. The fitting formula in a matter-dominated Universe ($Ω_0=Ω_M=1$) is a function of wavenumber $k$, redshift $z$ and four cosmological parameters: the density of massive neutrinos, $Ω_ν$, the number of massive neutrino species, $N_ν$, the baryon density, $Ω_{b}$ and the dimensionless Hubble constant, $h$. Our formula is accurate in a broad range of parameters: $k\le 100 h/Mpc$, $z\le 30$, $Ω_ν\le 0.5$, $N_ν\le 3$, $Ω_{b}\le 0.3$, $0.3\le h\le 0.7$. The deviation of the variance of density fluctuations calculated with our formula from numerical results obtained with CMBfast is less than 6% for the entire range of parameters. It increases with $Ω_bh^{2}$ and is less than $\le 3%$ for $Ω_bh^{2}\le 0.05$. The performance of the analytic approximation of MDM power spectra proposed here is compared with other approximations found in the literature. Our approximation turns out to be closest to numerical results in the parameter space considered here.

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arXiv1999

Spatial correlation function of quasars and power spectrum of cosmological matter density perturbations

We examine the dependence of the spatial two-point correlation function of quasars $ξ_{qq}(r,z)$ at different redshifts on the initial power spectrum in flat cosmological models. Quasars and other elements of the large-scale structure of the universe are supposed to form in the peaks of the scalar Gaussian field of density fluctuations of appropriate scales. Quasars are considered as a manifestation of short-term active processes at the centers of these fluctuations. We propose a method for calculating the correlation function $ξ_{qq}(r,z)$ and show its amplitude and slope to depend on the shape of the initial power spectrum and the scale R of the fluctuations in which quasars are formed. We demonstrate that in the CDM models with the initial power spectrum slope $n=0.7\div1$ it is possible to explain, by choosing appropriate values of R, how the amplitudes and correlation radii of $ξ_{qq}(r,z)$ may either increase or decrease with increasing redshift z. In particular, the correlation radii of $ξ_{qq}(r,z)$ grow from $6-10h^{-1}$ Mpc when R grows from $0.45 h^{-1}$ to $1.3h^{-1}$ Mpc. The H+CDM model at realistic values of R fails to account for the observational data according to which the $ξ_{qq}(r,z)$ amplitude decreases with increasing $z$.

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arXiv1998

The number density of quasars as a probe of initial power spectrum on small scale

The dependence of the number density of the bright QSOs at different redshifts ($n_{QSO}(z)$) on initial power spectrum is studied. It is assumed that QSO phenomenon is an early short term stage of evolution of massive galaxies with $M\geq 2\times 10^{11}h^{-1}M_{\odot}$. The duration of such QSO stage which is passed through by fraction $α$ of galaxies is determined by means of minimization of the divergence of the theoretical number density of QSOs at different redshifts for specified initial spectrum from observable one \cite{sc91}. It is shown that the nearest number densities of QSOs at $0.7\le z\le 3.5$ to observable ones are obtained for the tilted CDM model ($Ω_{b}=0.1$, $n=0.7$). The QSO stage lasts $\sim 7\times 10^{7}/α$ years and begins soon after the moment of rise of the first counterflow in collisionless component and shock wave in gas. The possibility of the reconstruction of initial power spectrum on small scale on the base of the observable data on number density of QSOs at different $z$ is considered too. Such reconstructed spectrum in comparison with standard CDM has steep reducing of power at $k\ge 0.5 h Mpc^{-1}$.

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arXiv1998

Large scale structure formation in mixed dark matter models with a cosmological constant

We study linear power spectra and formation of large scale structures in flat cosmological models with $Λ\ge 0$ and cold plus hot dark matter components (MLM). The hot component consists of massive neutrinos with cosmological density $Ω_H$. The linearized Einstein-Boltzmann equations for the evolution of the metric and density perturbations are integrated for a set of values of the cosmological parameters. For all the considered models we assume a scale-invariant primeval spectrum. The density weighted final linear power spectra are normalized to the four year COBE data and have been used to constrain the parameter space by a comparison of linear predictions with the current observational data on large scales. The consistency of MLM predictions with the observable data set is best obtained for models with one specie of massive neutrinos and $Ω_H/Ω_M \le0.2$. For this class of MLM models we obtain constraints from linear data on the present matter density. Consistency with the estimated cluster abundance can be achieved for COBE normalized MLM models with $Ω_H/Ω_M\le0.2$ and $ 0.45 \le Ω_M \le 0.75$ for $h=0.5$. If $h=0.7$ then $ 0.3 \le Ω_M \le 0.5$. These constraints are at $1σ$ level and standard MDM models are clearly ruled out. We note that the range of allowed values for $Ω_M$, that we obtain for MLM models from linear analysis, is also approximately the same range that is needed in order to consistently satisfy a variety of independent observational constraints.

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