arXiv subjects

A. A. Vasylenko

Publications and source records attributed to A. A. Vasylenko.

11 recordsLinked to original sources

arXiv2026

Milky Way Near Twins (MWNeTs). I. A Hierarchical Framework for Identifying the Evolutionary Counterparts of the Milky Way

The search for Milky Way (MW) analogues has traditionally relied on similarity in a limited set of present-day global properties, including morphology. However, galaxies with similar current properties may have experienced different assembly histories, secular evolution, nuclear activity, and environmental histories. We introduce Milky Way Near Twins (MWNeTs) as galaxies that resemble the Milky Way in present-day properties and exhibit observational signatures consistent with broadly similar evolutionary pathways. We reformulate the search for the closest extragalactic counterparts of the MW by shifting from parameter-based similarity toward evolutionary similarity. We propose a hierarchical methodology consisting of five stages: isolation and cosmic-web context, morphological and structural constraints, nuclear activity and supermassive black hole properties, global spectrophotometric and dynamical constraints, and advanced evolutionary diagnostics. The first four stages identify galaxies consistent with the present-day environmental, structural, nuclear, spectrophotometric, and dynamical state of the MW, while the fifth stage tests this similarity using independent signatures of comparable evolutionary histories. We introduce the concept of evolutionary memory, in which complementary diagnostics preserve information about physical processes operating on different timescales and probing different layers of galaxy formation and evolution. These diagnostics include the integrated spectral energy distribution, rotation-curve morphology, chemo-dynamical signatures, globular-cluster systems, merger history, circumgalactic-medium properties, and multiwavelength fossil tracers. Together, the MWNeT framework establishes an observational bridge between Galactic and extragalactic astronomy and supports future searches for the closest evolutionary counterparts of the Milky Way.

astro-ph.GA↗

arXiv2026

The 2MIG isolated AGNs -- 2. X-ray general properties and peculiarities

We have analysed a sample of 2MIG isolated galaxies hosting AGNs (isolated AGNs) to assess whether their nuclear activity differs from that in denser environments. The isolation criteria rule out interactions with other galaxies of similar evolutionary stage at least $\sim 3$~Gyr. We systematised the available \textit{Swift}, \textit{NuSTAR}, \textit{XMM-Newton}, \textit{Chandra}, and \textit{INTEGRAL} X-ray data for isolated AGNs at $z<0.05$, determining their general X-ray properties and peculiarities, spectral models, and supermassive black hole (SMBH) masses. We investigated the best spectral models for 20 isolated AGNs, including 9 sources fitted for the first time in this work. Our results indicate that an isolation of galaxies in the nearby Universe does not significantly affect nuclear activity. This conclusion is supported by the diversity of accretion types and the absence of any preference for a particular basic or composite spectral model. We note an interesting case for ESO~499$-$041, where the data-to-model ratio shows significant changes above 5~keV. These deviations from the continuum may tentatively indicate the presence of a relativistic iron line in the \textit{Chandra} spectrum of ESO~499$-$041 compared to the \textit{Swift} spectrum. We derived SMBH masses for 24/32 isolated AGNs applying the $M_{\rm BH}$--$σ_\star$ relation and used available estimates for 8/32. A general distribution is that 27/32 isolated AGNs host SMBHs with $M_{\mathrm{SMBH}} \lesssim 10^{8}\,M_\odot$. For the first time, we found evidence of the linear correlation between L$_{2-10, keV}$ and $\log M_{\mathrm{SMBH}}$ that is not observed in other AGNs samples. This trend may be affected by the limited sample size and requires further confirmation with larger datasets.

astro-ph.HE↗

arXiv2026

NGC 3521 as the Milky Way near twin: spectral energy distribution from UV to radio decameter ranges

Milky Way analogues (MWAs) are usually selected from structural and kinematic properties, but robust SED-based similarity criteria are limited by heterogeneous photometry and incomplete wavelength coverage. We present a homogeneous, aperture-photometry SED of the Milky Way near-twin NGC~3521 from the ultraviolet to the radio decameter range. Fluxes are measured within a fixed elliptical isophotal aperture using GALEX, SDSS, WISE, Spitzer/MIPS, Herschel/PACS+SPIRE, and VLA data, and supplemented by meter/decameter constraints. We report new observations obtained in Jan-Feb 2022 with the Ukrainian T-shape radio telescope and derive, for the first time, an upper limit in the 24--32~MHz band. The UV-to-decameter SED (27 points) is modelled with \textsc{CIGALE}, including a dedicated low-frequency radio prescription (\texttt{radio_extra}) that accounts for emission and absorption effects. Using ZTF and NEOWISE data (2014--2025), we detect genuine nuclear variability; optical trends at $\sim2^{\prime\prime}$ primarily trace the compact nucleus, while NEOWISE variability reflects a mix of nuclear changes and warm-dust emission within the larger aperture. The preferred fit yields $M_\star \simeq 6.0\times10^{10},M_\odot$, ${\rm SFR}\simeq1.65,M_\odot,{\rm yr}^{-1}$, $M_{\rm dust}\simeq1.3\times10^{8},M_\odot$, and an effective dust temperature of $\sim23$~K. The decameter constraint gives $S_{28,{\rm MHz}}<11.22$~Jy, consistent with expectations for a Milky Way-like system placed at 10.7~Mpc. We conclude that an integrated, homogeneous SED, especially below 100~MHz, provides a complementary diagnostic for identifying and validating MWAs and for interpreting how Milky Way properties would appear to an external observer.

astro-ph.GA↗

arXiv2026

Milky Way galaxy-analogs and isolated galaxies with bars: environmental density in the Local Volume

The environmental density of galaxies within the cosmic web constrains their 3D locations in filaments, voids, groups, and clusters. It traces the distribution of baryons and the influence of dark-matter halos on galaxy evolution, and helps diagnose external processes such as supernova and AGN feedback, tidal interactions, ram-pressure stripping, and large-scale flows. We focus on isolated barred galaxies, the parent population that includes Milky Way analogs. To measure local environmental density and verify isolation (|Delta v| <= 500 km s^-1), we built a Python pipeline that works in two redshift regimes: low (z0 < 0.02) and high (z0 >= 0.02). Densities were estimated with k-nearest neighbors and Voronoi tessellations and classified as void (Sigma < 0.05), filament (0.05 <= Sigma < 0.5), group (0.5 <= Sigma < 2.0), and cluster (Sigma >= 2.0). Our northern-sky sample contains 311 isolated barred galaxies from 2MIG plus Milky Way analog systems (z < 0.07). We find 157 void, 84 filament, 27 group, and 11 cluster galaxies; 30 have no detected neighbors. Sixty-seven lie in extremely low-density regions (Sigma_3D < 0.01 gal Mpc^-3), and 22 have the nearest companion beyond 5 Mpc, indicating residence in extended voids. The Milky Way (Sigma_5NN ~ 0.13 gal Mpc^-3, R ~ 2.1 Mpc) and its close analog NGC 3521 both lie in filamentary environments at the edge of a nearby void. For z > 0.02 we identify three additional Milky Way analog candidates from the density metrics: CGCG 208-043 (3D Voronoi) and NGC 5231 and CGCG 047-026 (5th-nearest neighbor). These results show that local environmental density is an effective, physically motivated criterion for selecting Milky Way analogs.

astro-ph.GA↗

arXiv2025

Galaxy rotation curve based on RGB stars from the Gaia DR3 catalogue

In this paper, we construct a detailed circular velocity curve of the Milky Way out to 20 kpc based on the radial component of the Jeans equation in cylindrical coordinates, assuming an axisymmetric gravitational potential, and show its dependence on azimuth. We use only Gaia DR3 data and aim to minimize the use of model data and various assumptions. To build the rotation curves, we used a sample of 4,547,980 RGB stars with measured spatial velocities, covering the Galactic plane in the range of Galactocentric cylindrical coordinates $150^\circ < θ< 210^\circ$ and 0 < R < 20 kpc. We exclude systematics in the data that may arise from neglecting higher-order moments of the velocity distribution and their dispersions, as well as due to random measurement errors in Gaia. At the distance of the Sun, the circular velocity $V_{\rm c}(R_0)$ turned out to be ($229.63\pm0.30$) km s$^{-1}$, which is in good agreement with many previous estimates. The average slope of the circular velocity is $(-2.29\pm0.05)$ km s$^{-1}$ kpc$^{-1}$ obtained in the range of $R$ from 6 to 20 kpc and $θ$ from 150 to 210 degrees. The determined circular velocity curve has some peculiarities in behavior near $R\sim$13 and 18 kpc, but in general it does not contradict the results of other authors up to distances where our statistics are reliable.

astro-ph.GA↗

arXiv2024

Spatial orientation and shape of the velocity ellipsoids of the Gaia DR3 giants and subgiants in the Galactic plane

We present the results of determining the parameters characterizing the shape and orientation of residual velocity ellipsoids from the Gaia DR3 red giants and subgiants. We show the distribution of velocity dispersions in the Galactic plane obtained from three components of the spatial velocity, as well as the coordinate distribution of the intersection points of the velocity ellipsoid axes with the celestial sphere, in particular the deviations of the longitudes and latitudes of the vertices of stellar regions located within spheres with a radius of 1 kpc centered in the Galactic mid-plane. The area of the Galactic disk under study is in the range of Galactocentric coordinates 0 < R < 15 kpc and $120^\circ < θ< 240^\circ$. We show that the vertex deviations in some regions of the Galactic mid-plane can reach $30^\circ$ in longitude, and $15^\circ$ in latitude. This indicates the presence of kinematic distortions of the stellar velocity field, especially noticeable in the angular range of $150^\circ < θ< 210^\circ$ at a distance of approximately 13 kpc. We propose the angles of deviation of longitudes and latitudes of the ellipsoid axes of residual stellar velocities to be considered as kinematic signatures of various Galactic deformations determined from real fields of spatial velocities. We present the distribution of parameters characterizing the shapes of velocity ellipsoids, as well as their distribution of the semi-axes length ratios. We note a local feature in this distribution and in the distribution of the elongation measurements of the ellipsoids. We perform a comparison of the results obtained from the tensor of deformation velocities and from the observed spatial velocities.

astro-ph.GA↗

arXiv2020

Nuclear obscuration structure in Mrk 417 based on NuSTAR and Swift/BAT data

We present the results of X-ray spectral analysis of the Seyfert type 2 galaxy Mrk 417 observed by the NuSTAR (3-60 keV) and the Swift/BAT (14-150) observatories. The NuSTAR data shows a good fit with a baseline model which composed of an absorbed cutoff power-law component and reflected emission from the cold neutral medium. We found that the spectrum is steep $Γ= 1.63_{-0.11}^{+0.10}$ and obscured by hydrogen column density of $N_{H} = 3.22_{-0.39}^{+0.41} \cdot 10^{23} cm^{-2}$, narrow $FeK_α$ emission line has an equivalent width of $EW = 115_{-1}^{+2}$ eV that suggests this feature is originated in a moderate density of obscurer. In combining NuSTAR data with Swift/BAT spectrum we also applied a more physically motivated approach using complex physical models MYTorus and BNTorus. For the first case the photon index of $Γ_{MYTorus} = 1.68_{-0.09}^{+0.09}$ and the line-of-sight column density of the absorber $N_{H,l.o.s} = 3.36_{-0.07}^{+0.04} \cdot 10^{23} cm^{-2}$. Applying BNTorus model shows the photon index $Γ_{BNTorus} = 1.75_{-0.09}^{+0.09}$ and absorption $N_{H,l.o.s} = 3.72_{-0.39}^{+0.49} \cdot 10^{23} cm^{-2}$. Based on the results we get an estimation of gas-dust torus covering factor $f_{c} = 0.29-0.34$ and an intrinsic X-ray luminosity in 2-10 keV of $\approx 3.16\cdot 10^{43}$ erg/s. Further analysis of Mid-Infrared (MIR) observational data, indicates that the covering factor maybe even smaller $f_{c} \approx 0.12$. Our results allow us to suggest that obscuring material of Mrk 417 has preferably a ring-like geometry.

astro-ph.HE↗

arXiv2015

X-Ray Spectral Parameters for a Sample of 95 Active Galactic Nuclei

We present a broadband X-ray analysis of a new homogeneous sample of 95 active galactic nuclei (AGN) from the 22-month Swift/BAT all-sky survey. For this sample we treated jointly the X-ray spectra observed by XMM-Newton and INTEGRAL missions for the total spectral range of 0.5-250 keV. Photon index Γ, relative reflection R, equivalent width of Fe $K_α$ line (EW Fe $K_α$), hydrogen column density $N_{H}$, exponential cut-off energy $E_{c}$ and intrinsic luminosity $L_{corr}$ are determined for all objects of the sample. We investigated correlations Γ- R, EW Fe $K_α$ - $L_{corr}$, Γ- $E_{c}$, EW Fe $K_α$ - $N_{H}$. Dependence Γ- R for Seyfert 1 and 2 type of galaxies has been investigated separately. We found that the relative reflection parameter at low power-law indexes for Seyfert 2 galaxies is systematically higher than for Seyfert 1 ones. This can be related to an increasing contribution of the reflected radiation from the gas-dust torus. Our data show that there exists some anticorrelation between EW Fe $K_α$ and $L_{corr}$, but it is not strong. We have not found statistically significant deviations from the AGN Unified Model.

astro-ph.HE↗

arXiv2014

Controlling the transport of electrons on superfluid $^{4}$He in symmetric and asymmetric FET-like structures

When floating on a two-dimensional (2D) surface of superfluid $^{4}$He, electrons arrange themselves in 2D crystalline structure known as Wigner crystal. In channels, the boundaries interfere the crystalline order and in case of very narrow channels one observes a quasi-1D Wigner crystal formed by just a few rows of electrons and, ultimately, one row, i.e., in the ``quantum wire'' regime. Recently, the ``quantum wire'' regime was accessed experimentally [D. Rees {\it et al.}, Phys. Rev. Lett. {\bf 108}, 176801 (2012)] resulting in unusual transport phenomena such as, e.g., oscillations in the electron conductance. Using molecular dynamics simulations, we study the nonlinear transport of electrons in channels with constrictions: single and multiple symmetric and asymmetric geometrical constrictions with varying width and length, and saddle-point-type potentials with varying gate voltage. We analyze the average particle velocity versus driving force or the gate voltage. We have revealed a significant difference in the dynamics for long and short constrictions: the oscillations of the average particle velocity for the systems with short constrictions exhibit a clear correlation with the transitions between the states with different numbers of rows of particles while for longer constrictions these oscillations are suppressed. The obtained results are in agreement with the experimental observations. We proposed a FET-like structure that consists of a channel with asymmetric constrictions. We show that applying a transverse bias results either in increase of the average particle velocity or in its suppression thus allowing a flexible control tool over the electron transport. Our results bring important insights into the dynamics of electrons floating on the surface of superfluid $^{4}$He in channels with constrictions and allow an effective control over the electron transport.

cond-mat.mes-hall↗

arXiv2013

Observations of Sy2 galaxy NGC 3281 by XMM-Newton and INTEGRAL satellites

We present here the results of our analysis of X-ray properties of Seyfert 2 galaxy NGC 3281, based on the observational data obtained by XMM-Newton and INTEGRAL within the energy ranges 0.2-12 keV and 20-150 keV, respectively. The XMM-Newton spectrum of this object is presented for the first time. We show that fitting the X-ray spectrum of this galaxy with models based on the reflection from the disc with infinite column density yields non-physical results. More appropriate fit takes into account both transmitted and reflected emission, passed through a gas-dusty torus-like structure. Keeping this in mind, to model the inhomogeneous clumpy torus, we used the MYTorus model. Hence, we propose that the torus of NGC 3281 is not continuous structure, but it consists of separate clouds, which is in a good agreement with the results of near-IR observations. Using this assumption, we found that the torus inclination angle and the hydrogen column density are 66.98^{+2.63}_{-1.34} degrees and 2.08^{+0.35}_{-0.18}x10^{24} cm^{-2}, respectively. Also, the emission of the hot diffuse gas with temperature ~590 eV and warm absorption were detected.

astro-ph.HE↗

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↗