arXiv subjects

B. Novosyadlyj

Publications and source records attributed to B. Novosyadlyj.

At least 37 records · Page 2Linked to original sources

arXiv2010

Space number density of bright quasars in the halo model of galaxy formation

We analyse the redshift dependence of space number density of quasars assuming that they are the short-lived active stages of the massive galaxies and arise immediately after the collapse of homogeneous central part of protogalaxy clouds. Obtained dependence fits the observational data ChaMP+CDF+ROSAT (Silverman et al. 2005) very well for protogalaxy clouds of mass $M\approx 8\cdot 10^{11}$ $h^{-1}M_{\odot}$ and ellipticity $e<0.4$. The lifetime of bright X-ray AGNs or QSOs with $L_X>10^{44.5}$ erg$\cdot s^{-1}$ in the range of energies $0.3-8$ keV is $τ_{QSO}\sim 6\cdot10^6$ years when the mass of supermassive black hole is $M_{SMBH}\sim 10^{9}$ $M_{\odot}$ and the values of other quasar parameters are reasonable. The analysis and all calculations were carried out in the framework of $Λ$CDM-model with parameters determined from 5-years WMAP, SNIa and large scale structure data (Komatsu et al. 2009). It is concluded, that the halo model of galaxy formation in the $Λ$CDM cosmological model matches well observational data on AGNs and QSOs number density coming from current optical and X-ray surveys.

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arXiv2009

Evolution of scalar perturbations in cosmology with quintessential dark energy

The dynamics of expansion of the Universe and evolution of scalar perturbations are studied for the quintessential scalar fields $Q$ with the classical Lagrangian satisfying the additional condition $w=const$ or $c^2_a=0$. Both quintessential fields are studied for the same cosmological model. The systems of evolutionary equations for gauge-invariant perturbations of metrics, matter and quintessence have been analysed analyticaly for the early stage of the Universe life and numerically up to the present epoch. It is shown that amplitudes of the adiabatic matter density perturbations grow like in $Λ$CDM-model but time dependences of amplitudes of the quintessence perturbations are more varied: gauge-invariant variables $D_g^{(Q)}$ and $D_s^{(Q)}$ decay from initial constant value after entering the particle horizon while $D^{(Q)}$ and $V^{(Q)}$ grow at the early stage before entering the horizon and decay after that -- in the quintessence-dominated epoch, when gravitational potential starts to decay -- so, that at the current epoch they are approximately two orders lower than matter ones at the supercluster scale. Therefore, at the subhorizon scales the quintessential scalar fields are smoothed out while the matter clusters. It is also shown that both quintessential scalar fields suppress the growth of matter density perturbations and the amplitude of gravitational potential. In these QCDM-models -- unlike $Λ$CDM ones -- such suppression is scale dependent and more visible for the quintessence with $c^2_a=0$.

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arXiv2009

Power spectrum of electron number density perturbations at cosmological recombination epoch

The power spectrum of number density perturbations of free electrons is obtained for the epoch of cosmological recombination of hydrogen. It is shown that amplitude of the electron perturbations power spectrum of scales larger than acoustic horizon exceeds by factor of 17 the amplitude of baryon matter density ones (atoms and ions of hydrogen and helium). In the range of the first and second acoustic peaks such relation is 18, in the range of the third one 16. The dependence of such relations on cosmological parameters is analysed too.

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arXiv2008

Large-scale structure formation in cosmology with classical and tachyonic scalar fields

The evolution of scalar perturbations is studied for 2-component (non-relativistic matter and dark energy) cosmological models at the linear and non-linear stages. The dark energy is assumed to be the scalar field with either classical or tachyonic Lagrangian and constant equation-of-state parameter w. The fields and potentials were reconstructed for the set of cosmological parameters derived from observations. The comparison of the calculated within these models and experimental large-scale structure characteristics is made. It is shown that for w=const such analysis can't remove the existing degeneracy of the dark energy models.

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arXiv2008

Scalar Field as Dark Energy Accelerating Expansion of the Universe

The features of a homogeneous scalar field $ϕ$ with classical Lagrangian $L=ϕ_{;i}ϕ^{;i}/2-V(ϕ)$ and tachyon field Lagrangian $L=-V(ϕ)\sqrt{1-ϕ_{;i}ϕ^{;i}}$ causing the observable accelerated expansion of the Universe are analyzed. The models with constant equation-of-state parameter $w_{de}=p_{de}/ρ_{de}<-1/3$ are studied. For both cases the fields $ϕ(a)$ and potentials $V(a)$ are reconstucted for the parameters of cosmological model of the Universe derived from the observations. The effect of rolling down of the potential $V(ϕ)$ to minimum is shown.

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arXiv2008

WMAP2006: Cosmological Parameters and Large-scale Structure of the Universe

The parameters of cosmological model with cold dark matter and cosmological constant (Lambda CDM) have been determined on a basis of three-year cosmic microwave background observations by space mission WMAP, as well as the data on the large-scale structure of the Universe. The data cover scales from 1 up to 10000 Mpc. The best-fit values of LambdaCDM model parameters were found by minimization of chi^2 using the Levenberg-Markquardt approach (Omega_Lambda=0.736+-0.065, Omega_m=0.238+-0.080, Omega_b=0.05+-0.011, h=0.68+- 0.09, sigma_8=0.73+-0.08 and n_s=0.96+-0.015). It is shown that the LambdaCDM model with these values of the parameters agrees well with the angular power spectrum of cosmic microwave background and with power spectra of the density perturbations, estimated from spatial distributions of galaxies, rich galaxy clusters and from statistics of Ly_alpha absorption lines in spectra of distant quasars as well. The accordance of modeled characteristics of the large-scale structure with observable ones was analyzed, and possible reasons of significant discrepancies between some of them were considered.

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arXiv2006

Perturbations of ionization fractions at the cosmological recombination epoch

A development of perturbations of number densities of ions and electrons during recombination epoch is analysed. The equations for relative perturbations of ionization fractions were derived from the system of equations for accurate computation of the ionization history of the early Universe given by Seager et al. (1999,2000). It is shown that strong dependence of ionization and recombination rates on the density and temperature of plasma provides the significant deviations of amplitudes of ionization fractions relative perturbations from ones of baryon matter density adiabatic perturbations. Such deviations are most prominent for cosmological adiabatic perturbations of scales larger than sound horizon at recombination epoch. The amplitudes of relative perturbations of number densities of electrons and protons at last scattering surface exceed by factor of $\simeq$5 the amplitude of relative perturbation of baryons total number density, for helium ions this ratio reaches the value of $\simeq$18. For subhorizon cosmological perturbations these ratios appear to be essentially lesser and depend on oscillation phase at the moment of decoupling. These perturbations of number densities of ions and electrons at recombination epoch do not contribute to the intrinsic plasma temperature fluctuations but cause the ''corrugation'' of last scattering surface in optical depth, $δz_{dec}/(z_{dec}+1)\approx -δ_b/3$, at scales larger than sound horizon. It may result into noticeable changes of precalculated values of CMB polarization pattern at several degrees angular scales.

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arXiv2005

Gradient and dispersion analyses of the WMAP data

We studied the WMAP temperature anisotropy data using two different methods. The derived signal gradient maps show regions with low mean gradients in structures near the ecliptic poles and higher gradient values in the wide ecliptic equatorial zone, being the result of non-uniform observational time sky coverage. We show that the distinct observational time pattern present in the raw (cleaned) data leaves also its imprints on the composite CMB maps. Next, studying distribution of the signal dispersion we show that the north-south asymmetry of the WMAP signal diminishes with galactic altitude, confirming the earlier conclusions that it possibly reveals galactic foreground effects. As based on these results, one can suspect that the instrumental noise sky distribution and non-removed foregrounds can have affected some of the analyses of the CMB signal. We show that actually the different characteristic axes of the CMB sky distribution derived by numerous authors are preferentially oriented towards some distinguished regions on the sky, defined by the observational time pattern and the galactic plane orientation.

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arXiv2004

Dark Energy and Large-Scale Structure of the Universe

The evolution of matter density perturbations in two-component model of the Universe consisting of dark energy (DE) and dust-like matter (M) is considered. We have analyzed it for two kinds of DE with $ω\ne -1$: a) unperturbed energy density and b) perturbed one (uncoupled with matter). For these cases the linear equations for evolution of the gauge-invariant amplitudes of matter density perturbations are presented. It is shown that in the case of unperturbed energy density of DE the amplitude of matter density perturbations grow slightly faster than in the second case.

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arXiv2004

The constraints on power spectrum of relic gravitational waves from current observations of large-scale structure of the Universe

We carry out the determination of the amplitude of relic gravitational waves power spectrum. Indirect best-fit technique was applied to compare observational data and theory predictions. As observations we have used data on large-scale structure (LSS) of the Universe and anisotropy of cosmic microwave background (CMB) temperature. The conventional inflationary model with 11 parameters has been investigated, all of them evaluated jointly. This approach gave us a possibility to find parameters of power spectrum of gravitational waves along with statistical errors. The main result consists in following: WMAP data on power spectrum of CMB temperature fluctuations along with LSS data prefer model with small amplitude of tensor mode power spectrum, close to zero. The upper limit for its amplitude at quadupole harmonics T/S=0.6 at 95% C.L.

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arXiv2003

Spherical collapse and mass function of rich clusters in models with curvature and cosmological constant

We have analyzed the dependences of the threshold value of amplitude of linear density fluctuation collapsed at the current epoch, $δ_c$, and its overdensity after virialization, $Δ_c$, on matter density content, 3D curvature parameter and cosmological constant. Though the range for the threshold values of perturbation amplitude is quite narrow - $1.55\le δ_c\le 1.75$ in the region of parameters $-0.4\leΩ_k\le0.4$, $0\leΩ_Λ\le 1$, $0.1\leΩ_m\le 1$, the difference in the concentrations of rich clusters of galaxies (calculated within the Press-Schechter formalism framework) with real and with canonical values of $δ_c$ reaches, and for some models exceeds, 30%. The range of changes for the overdensity after virialization, $Δ_c$, is considerably wider for the same region of parameters: $60\leΔ_c\le180$. It results into difference up to $\sim40$% between the X-ray temperatures of gas, as calculated for these values and for the canonical value of $Δ_c=178$. Also we have found analytical approximations of the dependences $δ_c(Ω_m,Ω_Λ)$ and $Δ_c(Ω_m,Ω_Λ)$ with their accuracies for above mentioned region of parameters being no worse than 0.2% and 1.7% respectively.

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arXiv2002

Acoustic peaks and dips in the CMB power spectrum: observational data and cosmological constraints

The locations and amplitudes of three acoustic peaks and two dips in the last releases of the Boomerang, MAXIMA and DASI measurements of the cosmic microwave background (CMB) anisotropy power spectra as well as their statistical confidence levels are determined in a model-independent way. It is shown that the Boomerang-2001 data (Netterfield et al. 2001) fixes the location and amplitude of the first acoustic peak at more than 3σconfidence level. The next two peaks and dips are determined at a confidence level above 1σbut below 2σ. The locations and amplitudes of the first three peaks and two dips are 212+/-17, 5426+/-1218μK^2, 544+/-56, 2266+/-607μK^2, 843+/-35, 2077+/-876μK^2, 413+/-50, 1960+/-503μK^2, 746+/-89, 1605+/-650μK^2 respectively (1σerrors include statistical and systematic errors). The MAXIMA and DASI experiments give similar values for the extrema which they determine. The determined cosmological parameters from the CMB acoustic extrema data show good agreement with other determinations, especially with the baryon content as deduced from standard nucleosynthesis constraints. These data supplemented by the constraints from direct measurements of some cosmological parameters and data on large scale structure lead to a best-fit model which agrees with practically all the used experimental data within 1σ. The best-fit parameters are: Ω_Λ=0.64^{+0.14}_{-0.27}, Ω_{m}= 0.36^{+0.21}_{-0.11}, Ω_b=0.047^{+0.093}_{-0.024}, n_s=1.0^{+0.59}_{-0.17}, h=0.65^{+0.35}_{-0.27} and τ_c=0.15^{+0.95}_{-0.15} (plus/minus values show 1σupper/lower limits obtained by marginalization over all other model parameters). The best-fit values of Ω_ν and T/S are close to zero, their 1σupper limits are 0.17 and 1.7 respectively.

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arXiv2000

Cosmological parameters from complementary observations of the Universe

We use observational data on the large scale structure (LSS) of the Universe measured over a wide range of scales from sub-galactic up to horizon scale and on the cosmic microwave background anisotropies to determine cosmological parameters within the class of adiabatic inflationary models. We show that a mixed dark matter model with cosmological constant ($Λ$MDM model) and parameters $Ω_m=0.37^{+0.25}_{-0.15}$, $Ω_Λ=0.69^{+0.15}_{-0.20}$, $Ω_ν=0.03^{+0.07}_{-0.03}$, $N_ν=1$, $Ω_b=0.037^{+0.033}_{-0.018}$, $n_s=1.02^{+0.09}_{-0.10}$, $h=0.71^{+0.22}_{-0.19}$, $b_{cl}=2.4^{+0.7}_{-0.7}$ (1$σ$ confidence limits) matches observational data on LSS, the nucleosynthesis constraint, direct measurements of Hubble constant, the high redshift supernova type Ia results and the recent measurements of the location and amplitude of the first acoustic peak in the CMB anisotropy power spectrum. The best model is $Λ$ dominated (65% of the total energy density) and has slightly positive curvature, $Ω=1.06$. The clustered matter consists in 8% massive neutrinos, 10% baryons and 82% cold dark matter (CDM). The upper 2$σ$ limit on the neutrino content can be expressed in the form $Ω_νh^2/N_ν^{0.64}\le0.042$ or, via the neutrino mass, $m_ν\le4.0$eV. The upper 1(2)$σ$ limit for the contribution of a tensor mode to the COBE DMR data is T/S$<1(1.5)$. Furthermore, it is shown that the LSS observations together with the Boomerang (+MAXIMA-1) data on the first acoustic peak rule out zero-$Λ$ models at more than $2σ$ confidence limit.

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arXiv2000

Constraints on the tensor mode from large scale structure observations

Observational data on the large scale structure (LSS) of the Universe are used to establish an upper limit for the amplitude of the tensor mode marginalized over all other cosmological parameters within the class of adiabatic inflationary models. It is shown that the upper 1$σ$ limit for the contribution of a tensor mode to the COBE DMR data is T/S$<1$.

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arXiv2000

Constraints on the neutrino mass and the cosmological constant from large scale structure observations

The observational data on the large scale structure (LSS) of the Universe are used to establish the upper limit on the neutrino content marginalized over all other cosmological parameters within the class of adiabatic inflationary models. It is shown that the upper 2$σ$ limit on the neutrino content can be expressed in the form $Ω_νh^2/N_ν^{0.64}\le0.042$ or, via the neutrino mass, $m_ν\le4.0$eV.

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arXiv2000

Cosmological parameters from observational data on the large scale structure of the Universe

The observational data on the large scale structure (LSS) of the Universe are used to determine cosmological parameters within the class of adiabatic inflationary models. We show that a mixed dark matter model with cosmological constant ($Λ$MDM model) and parameters $Ω_m=0.37^{+0.25}_{-0.15}$, $Ω_Λ=0.69^{+0.15}_{-0.20}$, $Ω_ν=0.03^{+0.07}_{-0.03}$, $N_ν=1$, $Ω_b=0.037^{+0.033}_{-0.018}$, $n_s=1.02^{+0.09}_{-0.10}$, $h=0.71^{+0.22}_{-0.19}$, $b_{cl}=2.4^{+0.7}_{-0.7}$ (1$σ$ confidence limits) matches observational data on LSS, the nucleosynthesis constraint, direct measurements of the Hubble constant, the high redshift supernova type Ia results and the recent measurements of the location and amplitude of the first acoustic peak in the CMB anisotropy power spectrum. The best model is $Λ$ dominated (65% of the total energy density) and has slightly positive curvature, $Ω=1.06$. The clustered matter consists in 8% massive neutrinos, 10% baryons and 82% cold dark matter (CDM). It is shown that the LSS observations together with the Boomerang (+MAXIMA-1) data on the first acoustic peak rule out zero-$Λ$ models at more than $2σ$ confidence level.

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arXiv2000

Determination of cosmological parameters from large scale structure observations

The possibility of determining cosmological parameters on the basis of a wide set of observational data including the Abell-ACO cluster power spectrum and mass function, peculiar velocities of galaxies, the distribution of Ly-$α$ clouds and CMB temperature fluctuations is analyzed. Using a $χ^2$ minimization method, assuming $Ω_Λ+Ω_m =1$ and no contribution from gravity waves, we found that a tilted $Λ$MDM model with one sort of massive neutrinos and the parameters $n\approx 1.12$, $Ω_m\approx 0.4$ ($Ω_Λ\approx 0.6$), $Ω_{cdm}\approx 0.3$, $Ω_ν\approx 0.06$, $Ω_b\approx 0.04$ and $h\approx 0.7$ matches observational data best. $Ω_ν$ is higher for more species of massive neutrinos, $\sim 0.1$ for two and $\sim 0.13$ for three species. $Ω_m$ raises by $\sim 0.08$ and $\sim 0.15$ respectively. Varying only a subset of parameters and fixing the others shows also that the observational data set used here rules out pure CDM models with $h\ge 0.5$, scale invariant primordial power spectrum, zero cosmological constant and spatial curvature at a very high confidence level, $>99.99%$. The corresponding class of MDM models are ruled out at $\sim 95%$ C.L. It is notable also that this data set determines the amplitude of scalar fluctuations approximately at the same level as COBE four-year data. It indicates that a possible tensor component in the COBE data cannot be very substantial.

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arXiv2000

Cosmological parameters from large scale structure observations

The possibility of determining cosmological parameters on the basis of a wide set of observational data including the Abell-ACO cluster power spectrum and mass function, peculiar velocities of galaxies, the distribution of Ly-$α$ clouds and CMB temperature fluctuations is analyzed. Using a $χ^2$ minimization method, assuming $Ω_Λ+Ω_{\rm{matter}} =1 $ and no contribution from gravity waves, we found that a tilted $Λ$MDM model with one sort of massive neutrinos and the parameters $n=1.12\pm 0.10$, $Ω_m=0.41\pm 0.11$ ($Ω_Λ=0.59\pm0.11$), $Ω_{cdm}=0.31\pm 0.15$, $Ω_ν=0.059\pm 0.028$, $Ω_b=0.039\pm 0.014$ and $h=0.70\pm 0.12$ matches observational data best. The 1$σ$ (68.3%) confidence limits on each cosmological parameter, which are obtained by marginalizing over the other parameters, are $0.82\le n\le1.39$, $0.19\leΩ_m\le 1$ ($0\leΩ_Λ\le 0.81$), $0\leΩ_ν\le 0.17$, $0.021\le Ω_b\le 0.13$ and $0.38\le h\le 0.85$ $1.5\le b_{cl}\le 3.5$. Here $b_{cl}$ is the cluster bias parameter. The best-fit parameters for 31 models which are inside of $1σ$ range of the best model are presented. It is shown also that observational data set used here rules out the class of CDM models with $h\ge 0.5$, scale invariant primordial power spectrum, zero cosmological constant and spatial curvature at very high confidence level, $>99.99%$. The corresponding class of MDM models are ruled out at $\sim 95%$ C.L.

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