arXiv subjects

S. Apunevych

Publications and source records attributed to S. Apunevych.

10 recordsLinked to original sources

arXiv2018

Network analysis of the COSMOS galaxy field

The galaxy data provided by COSMOS survey for 1 by 1 degree field of sky are analysed by methods of complex networks. Three galaxy samples (slices) with redshifts ranging within intervals 0.88-0.91, 0.91-0.94 and 0.94-0.97 are studied as two-dimensional projections for the spatial distributions of galaxies. We construct networks and calculate network measures for each sample, in order to analyse the network similarity of different samples, distinguish various topological environments, and find associations between galaxy properties (colour index and stellar mass) and their topological environments. Results indicate a high level of similarity between geometry and topology for different galaxy samples and no clear evidence of evolutionary trends in network measures. The distribution of local clustering coefficient C manifests three modes which allow for discrimination between stand-alone singlets and dumbbells (0 <= C <= 0.1), intermediately (0 < C < 0.9) and clique (0.9 <= C <= 1) like galaxies. Analysing astrophysical properties of galaxies (colour index and stellar masses), we show that distributions are similar in all slices, however weak evolutionary trends can also be seen across redshift slices. To specify different topological environments we have extracted selections of galaxies from each sample according to different modes of C distribution. We have found statistically significant associations between evolutionary parameters of galaxies and selections of C: the distribution of stellar mass for galaxies with interim C differ from the corresponding distributions for stand-alone and clique galaxies, and this difference holds for all redshift slices. The colour index realises somewhat different behaviour.

astro-ph.CO↗

arXiv2010

Properties and uncertainties of scalar field models of dark energy with barotropic equation of state

The dynamics of expansion and large scale structure formation in the multicomponent Universe with dark energy modeled by the minimally coupled scalar field with generalized linear barotropic equation of state (EoS) are analyzed. It is shown that the past dynamics of expansion and future of the Universe -- eternal accelerated expansion or turnaround and collapse -- are completely defined by the current energy density of a scalar field and relation between its current and early EoS parameters. The clustering properties of such models of dark energy and their imprints in the power spectrum of matter density perturbations depend on the same relation and, additionally, on the "effective sound speed" of a scalar field, defined by its Lagrangian. It is concluded that such scalar fields with different values of these parameters are distinguishable in principle. This gives the possibility to constrain them by confronting the theoretical predictions with the corresponding observational data. For that we have used the 7-year WMAP data on CMB anisotropies, the Union2 dataset on Supernovae Ia and SDSS DR7 data on luminous red galaxies (LRG) space distribution. Using the Markov Chain Monte Carlo technique the marginalized posterior and mean likelihood distributions are computed for the scalar fields with two different Lagrangians: Klein-Gordon and Dirac-Born-Infeld ones. The properties of such scalar field models of dark energy with best fitting parameters and uncertainties of their determination are also analyzed in the paper.

astro-ph.CO↗

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.

astro-ph↗

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.

astro-ph↗

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.

astro-ph↗

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$<1$.

astro-ph↗

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.

astro-ph↗

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.

astro-ph↗

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.

astro-ph↗

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.

astro-ph↗