arXiv subjects

A. V. Tugay

Publications and source records attributed to A. V. Tugay.

15 recordsLinked to original sources

arXiv2025

Penrose hypothesis and instability of naked singularities in static spherically symmetric systems with scalar fields

General relativistic static spherically symmetric (SSS) asymptotically flat configurations with scalar fields typically contain naked singularities at the center. We consider minimally coupled scalar fields with power-law potentials leading to the Coulomb asymptotic of the field $ϕ(r)\approx Q/r$ for large values of the radial variable r. The configurations are uniquely defined by total mass and a Q-parameter characterizing the strength of the scalar field at spatial infinity. The focus is on the linear stability against radial (monopole) perturbations of the SSS configurations satisfying conditions of asymptotic flatness. Our numerical investigations show the existence of divergent modes of small perturbations against the static background, at least for sufficiently small values of Q. This means instability of the configurations, confirming the well-known Penrose conjecture about the nonexistence of naked singularities - in this particular case. On the other hand, we have not found divergent modes of linear radial perturbations for sufficiently large Q.

gr-qc↗

arXiv2024

What excites the optical emission in X-ray-selected galaxies?

We present a study of $1347$ galaxies at $z<0.35$ with detected nuclear X-ray emission and optical emission line diagnostics in the Baldwin-Phillips-Terlevich (BPT) diagram. This sample was obtained by cross-matching the X-ray Multi-Mirror Mission Observatory - Newton (XMM-Newton) DR10 catalogue with Sloan Digital Sky Survey (SDSS) DR17 galaxies with well-measured line ratios. The distribution of these sources in the BPT diagram covers all three excitation regimes: Ionized Hydrogen (HII) regions (23\%), `composites' (30\%), and Seyfert galaxies with the low ionization nuclear emission line regions (LINERs) (47\%). In contrast, the fraction of objects classified as active galactic nuclei (AGN) in the SDSS subsample selected for cross-match with XMM-Newton is only 13\%. This fact illustrates that X-ray emission from galaxies commonly points towards the presence of AGN. Our data show, for the first time, a clear dependence of the BPT position on the ratio of the X-ray to $Hα$ fluxes. Sources dominated by X-ray emission lie in the Seyfert and LINER regimes of the BPT diagram. Most sources with a low X-ray-to-$Hα$-luminosity ratio, $log_{10}(L_X/L_{Hα}) < 1.0$, lie in the HII regime. In our sample, there are even 45 galaxies that have $L^{Star}_{XR}/L^{Total}_{Xray}>0.5$. In contrast, the positions of the sample members in the BPT diagram exhibit {no} dependence on the X-ray hardness ratio. Our finding suggests that the X-ray-to-$Hα$ ratio can help us to differentiate galaxies whose X-ray flux is dominated by an AGN {from galaxies with} central X-ray binaries and other stellar X-ray sources.

astro-ph.GA↗

arXiv2018

Numerical Estimator for Large-Scale Cosmic Structures

Components of large-scale structure (LSS) of Universe includes galaxy clusters, walls, filaments, groups and field galaxies. The question of spatial organization of all these components remains open despite of a number of recently developed methods of LSS analysis. In this paper we introduce new continuous structural parameter of galaxy distribution for the determinig of the type of LSS surrounding. This parameter is based on comparison of the radial distribution of galaxies around the certain point with the uniform one. Our method for structure parameter calculation is based on the distribution of 1000 closets galaxies to the selected one. Such number was selected because most galaxy clusters contains up to 1000 galaxies. When we exceed 1000th closest galaxy we will leave possible cluster or filament and will pass to another type of LSS. We suppose that in uniform distribution of galaxies their number should increase as third power a distance, similar to luminosity. Therefore the inverse dependence of galaxy distance from number should be cubic root. New structural parameter was introduced as the difference of this dependence of cubic root. The main type of cosmic surrounding for a galaxy is defined by the value and the sign of such structural parameter. If a galaxy lie in a cluster the distances of nearby galaxies will be less than cubic root. We integrated distance difference for all 1000 galaxies and get negative stuctural parameter in this case. In the case of void the structural parameter will be positive. New parameter was calculated for sky distribution of SDSS galaxies at distances from 50 to 150 Mpc. Analysing obtained values, we come to conclusion that our structural parameter can be used for the division of LSS components and extragalactic filament detection.

astro-ph.CO↗

arXiv2018

Luminosity - Spectral Index Dependence of X-ray Bright Seyfert Galaxies

X-ray luminosities and spectral indices of 97 bright Seyfert 1 galaxies from XMM archive are analyzed in this article. Distribution of these values is random so we conclude that the model of emission should be at least two-parametric. Within the merging model of AGN the relation between black hole mass, stage of merging and observable X-ray parameters is proposed.

astro-ph.GA↗

arXiv2018

X-ray Emission and Orientation of Selected PF Galaxy Clusters

X-ray counterparts for 35 galaxy clusters contained in the PF catalog of galaxy clusters and groups were found in XMM-Newton archive. 22 ones (all from ACO catalogue) have extended elliptic X-ray haloes appropriate for determination of orientation. Position angles and eccentricities were calculated and compared with cluster orientations optical band.

astro-ph.CO↗

arXiv2018

Determination of the Galaxy Cluster Orientation Using X-ray Images by FOCAS Method

In our work we considered orientations of bright X-ray halos of the galaxy clusters (mainly Abell clusters). 78 appropriate clusters were selected using data from Xgal sample of extragalactic objects in XMM-Newton observation archive. Position angles and eccentricities of these halos were calculated applying FOCAS method. No privileged orientations were found.

astro-ph.CO↗

arXiv2018

Statistical Analysis of Large-Scale Structure of Universe

While galaxy cluster catalogs were compiled many decades ago, other structural elements of cosmic web are detected at definite level only in the newest works. For example, extragalactic filaments were described by velocity field and SDSS galaxy distribution during the last years. Large-scale structure of the Universe could be also mapped in the future using ATHENA observations in X-rays and SKA in radio band. Until detailed observations are not available for the most volume of Universe, some integral statistical parameters can be used for its description. Such methods as galaxy correlation function, power spectrum, statistical moments and peak statistics are commonly used with this aim. The parameters of power spectrum and other statistics are important for constraining the models of dark matter, dark energy, inflation and brane cosmology. In the present work we describe the growth of large-scale density fluctuations in one- and three-dimensional case with Fourier harmonics of hydrodynamical parameters. In result we get power-law relation for the matter power spectrum.

astro-ph.CO↗

arXiv2018

X-ray Emission of ICRF Sources

Considering increasing requirements to the coordinates measurement precision by the end of XX century International Astronomical Union commenced implementation of the new astrometric system ICRF (International Celestial Reference Frame). This quasi-inertial reference frame system centered in the barycenter of the Solar System and has axes defined by the positions of distant extragalactic sources - frames. Unlike equatorial system ICRF has no shortcomings of the coordinates identification due to the Earth axis precession, stellar proper motions and other factors. Extragalactic frames of the ICRF system are mostly quasars, radio galaxies, blazars and Seyfert galaxies i.e. different types of the active galaxy nuclei (AGN). Active galaxy nuclei are characterized by processes with significant. Such processes quite often are followed by X-ray emission generation. The purpose of this work is to consider X-ray emission of ICRF sources and features of their possible proper motions. Among 295 selected reference frames of the system we identified 54 X-ray sources which were observed by space observatory XMM Newton and noticed rapid variability of the blazars 2E 2673 (W Com) and 2E 1802 which enables to conclude that they have some very active processes in the sources centers. With regards to the future more detailed analysis we beleive that evidences of the objects proper motion could be found in their spectra. Based on the constructed luminosity and spectral graphs we could conclude that apart from above mentioned AGNs rest 52 objects do not show veriability and special attention should be paid to blazars within ICRF system development and use. Major part of the X-ray sources between the reference frames are stable.

astro-ph.HE↗

arXiv2018

Simulation of Large-Scale Structure of Universe by Gaussian Random Fields

Large-scale structure of Universe includes galaxy clusters connected by filaments. Voids occupy the rest of cosmic volume. The search of any dependencities in filament structure can give answer to more general questions about origin of structures in the Universe. This becomes possible because, according to current picture of Universe, one could simulate the evolution of Universe until its very beginning or vice versa. According to current cosmological hydrodynamical theories a number of computer simulations of LSS were performed to describe its properties. In this work we consider alternative variant of simulating the distribution of matter that is very similar to real. We simulated two-dimensional galaxy distribution on the sky using random distributions of clusters and single galaxies. The main assumption was that matter clusterised to initial density fluctuations with uniform distribution. According to Zeldovich theory, low-dimensional anisotropies should increase, that corresponds to appearance of filaments in 2D case. Thus we generated a net of filaments between clusters with certain length limits. Real galaxy distribution was simulated by random changing galaxy positions in filaments and clusters. We generated radial distributions of galaxies in clusters taking into account the surrounding and add uniform distribution of isolated galaxies in voids. Our model has been coordinated with SDSS galaxy distribution with using two-point angular correlation function. Parameters of random distributions were found for the case of equality of correlation function slope for the model and for observational data.

astro-ph.CO↗

arXiv2014

Surface Brightness Profiles of Seyfert Galaxies

We built r-band surface brightness profiles by SDSS data for 16 Seyfert galaxies observed in Crimean Astrophysical Observatory. Obtained profiles can be used for finding more accurate lightcurves for these galaxies.

astro-ph.GA↗

arXiv2013

Bright X-ray galaxies in SDSS filaments

Eighteen bright X-ray emitting galaxies were found in nearby filaments within SDSS region. Basic X-ray spectral parameters were estimated for these galaxies using power law model with photoelectric absorption. A close pair of X-ray galaxies was found.

astro-ph.GA↗

arXiv2012

Angular and spatial clustering of photometrically classified quasar candidates from SDSS NBCKDE

The present paper analyses the quasar clustering using the two-point correlation function (2pCF) and the largest existing sample of photometrically selected quasars: the SDSS NBCKDE catalogue (from the SDSS DR6). A new technique of random catalogue generation was developed for this purpose, that allows to take into account the original homogeneity of the survey without knowledge of its imaging mask. When averaged over photometrical redshifts 0.8<z_phot<2.2 the 2pCF of photometrically selected quasars is found to be approximated well with the power law w(θ)=(θ/θ_0)^{-α} with θ_0=4".5+/-1".4, α=0.94+/-0.06 over the range 1'<θ<40'. It agrees well with previous results by Myers et al. (2006,2007), obtained for samples of NBCKDE quasars with similar mean z_phot, but averaged over broader z_phot range. The parameters of the deprojected 2pCF averaged over the same z_phot range and modelled with a power law ξ(r)=(r/r_0)^{-γ}, are r_0=7.81^{+1.18}_{-1.16} Mpc/h, γ=1.94+/-0.06, which are in perfect agreement with previous results from spectroscopic surveys. We confirm the evidence for an increase of the clustering amplitude with z, and find no evidence for luminosity dependence of the quasar clustering. The latter is consistent with the models of the quasar formation, in which bright and faint quasars are assumed to be similar sources, hosted by dark matter halos of similar masses, but observed at different stages of their evolution. Comparison of our results with studies of the X-ray selected AGNs with similar z shows that the clustering amplitude of optically selected quasars is similar to that of X-ray selected quasars, but lower than that of samples of all X-ray selected AGNs. As the samples of all X-ray selected AGNs contain AGNs of both types, our result serves as an evidence for different types of AGNs to reside in different environments.

astro-ph.CO↗

arXiv2010

Correlation function of quasars in real and redshift space from the Sloan Digital Sky Survey Data Release 7

We analyze the quasar two-point correlation function (2pCF) within the redshift interval $0.8 10\,h^{-1}$ Mpc the parameter describing the large-scale infall to density inhomogeneities is $β=0.63\pm0.10$ with the linear bias $b=1.44\pm0.22$ that marginally (within 2$σ$) agrees with the linear theory of cosmological perturbations. We discuss possibilities to obtain a statistical estimate of the random component of quasars velocities (different from the large-scale infall). We note rather slight dependence of quasars velocity dispersion upon the 2pCF parameters in the region $r<2$ Mpc.

astro-ph.CO↗

arXiv2009

XMM-Newton Observations of X-ray Pulsar Cen X-3

We present the results of our study of X-ray pulsar Cen X-3 using XMM-Newton observations. The light curve and the spectrum for this observations were built and Fe triplet within 6.5-7 keV region was detected. The geometric model of relativistic accretion disk for iron emission lines Fe I K alpha, Fe XXV and Fe XXVI in 6.4-7.0 keV region was applied. The values of disc inclination, inner and outer radii of the disc and mass of the central compact object (neutron star) were obtained. Intensity variations of these lines during orbital motion were also detected. The largest variation was detected for Fe I K alpha line, that agrees with the results of other authors. These results conform the model in which Fe I K alpha line forms in hot plasma of accretion disc and highly ionized iron lines form in outer regions of binary system. Probably the most interesting feature of Cen X-3 spectrum is Fe XXV triplet which was found by Iaria et al. (2005) from Chandra data analysis. We did not find this triplet in our analysis of XMM-Newton data and explain its absence by the insufficient energy resolution of XMM-Newton instruments.

astro-ph.HE↗

arXiv2005

New list of peculiar velocities of RFGC galaxies

We present a new version of the list of peculiar velocities of 1561 flat edge-on spirals from the RFGC catalogue. It differs from the previous version by 233 new data and 34 corrected data. A new regression was used for distances estimation based on the Tully-Fisher relationship in the "linear diameter - HI line width" variant. Moreover, we present velocities for 3 models of galaxies collective motion. They are a D-model (dipole, Hubble expansion + bulk motion with constant speed), DQ-model (a quadrupole terms are added) and DQO-model (DQ-model + octopole).

astro-ph↗