arXiv subjects

O. V. Kompaniiets

Publications and source records attributed to O. V. Kompaniiets.

11 recordsLinked to original sources

arXiv2026

Revealing a multi-zone circumnuclear dust response in UGC~11487 through phase-resolved WISE W1--W2 diagnostics

Mid-infrared (MIR) flares provide a direct probe of dust reprocessing in obscured tidal disruption event (TDE) candidates when the primary optical or ultraviolet flare is weak, missed, or strongly attenuated. We present a phase-resolved analysis of the WISE/NEOWISE W1-W2 evolution of the MIR-selected TDE candidate UGC 11487/WTP14adeqka over 2014-2024. We combine timing, colour, and flux diagnostics with phenomenological modelling, hydrodynamically motivated clumpy dust-echo calculations, and an aperture-matched ultraviolet-to-radio spectral energy distribution of the host. The decade-long flare shows a delayed and broader W2 response, colour hysteresis, and cooling from approximately 900 K to 500-600 K. Positive-fluence centroids yield a preferred delay of $224 +/- 45$ d, corresponding to $0.188 +/- 0.038$ pc. The effective infrared luminosity peaks at approximately $3 x 10^{43}$ erg s$^{-1}$, and the integrated infrared energy is $(2.9-3.8) x 10^{51}$ erg. A single self-similar MIR response is strongly disfavoured, with Delta BIC = 281.7, while the preferred compact description is a two-component phenomenological model. Representative hydro-clumpy calculations reproduce the empirical diagnostics in a structured, multi-zone dust-response scenario. The host is a moderately star-forming isolated barred disc without a dominant persistent active galactic nucleus component. These results support an obscured TDE-like accretion transient reprocessed by structured circumnuclear dust and show that phase-resolved WISE diagnostics can recover characteristic sub-parsec response scales in obscured accretion-powered nuclear transients.

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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.

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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.

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arXiv2026

The 2MIG isolated AGNs. 3. Optical--IR variability and dust reverberation in the NLSy1 galaxies Mrk~42 and Mrk~493

This work presents the first dedicated optical--mid-infrared time-domain variability and dust-reverberation analysis of the isolated NLSy1 galaxies Mrk 42 and Mrk 493. We combine ZTF optical light curves, WISE mid-infrared monitoring, archival Swift and SDSS data, and high-cadence IAC80 optical observations. Using colour--magnitude relations, flux--flux analysis, and interpolated cross-correlation functions, we trace variable optical continuum and delayed dust response. Both galaxies show positive optical--MIR lags consistent with dust reverberation. For Mrk 493, we measure an observed-frame g--W1 lag of $τ_{\rm obs}=79.4\pm2.2$ d, corresponding to $R_{\rm dust}(W1)\simeq0.0648$ pc. For Mrk 42, the corresponding lag is $τ_{\rm obs}=39.1\pm2.6$ d, giving $R_{\rm dust}(W1)\simeq0.0320$ pc. These lags provide optical--MIR dust-reverberation radii and BLR--dust scale comparisons for both objects; the resulting $R_{\rm dust}/R_{\rm BLR}$ ratios are $\simeq6.8$ for Mrk 493 and $\sim6$--7 for Mrk 42. For Mrk 42, we derive the first host-subtracted AGN continuum luminosity at 5100 Å from SDSS spectral decomposition, giving a self-consistent BLR--dust comparison on an AGN-only luminosity basis. Both galaxies have similar radial hierarchies but different colour behaviour: Mrk 493 shows significant optical and MIR bluer-when-brighter trends, whereas Mrk 42 shows strong optical but weak MIR colour variability. We also identify and analyse a major optical flare in Mrk 42 with four internal maxima spaced by 45--47 d. We interpret this signal as quasi-periodic substructure within a broader accretion-driven flare, rather than as a strictly coherent periodic process. These results indicate that, even in dynamically isolated environments, the variability of low-mass, high-accretion-rate AGNs is governed mainly by the intrinsic state of the accretion flow and its coupling to circumnuclear dust.

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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.

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arXiv2026

NGC3521 as the Milky Way analogue: spectral energy distributon from UV to Radio and photometric variability

We studied the multiwavelength properties of NGC 3521, the Milky Way galaxy-twin, from UV- to radio, exploring the data from GALEX for UV-, SDSS for optical, 2MASS, WISE, MIPS (Spitzer) and PACS, SPIRE (Herschel) for IR-, and NRAO VLA for radio ranges. To obtain the spectral energy distribution (SED), we exploited the CIGALE software and constructed SEDs without (model A) and with (model B) AGN module. The type of nuclear activity of NGC 3521 is confirmed as the LINER. We also present the results of the photometric data processing. Exploring the ZTF observations in 2018-2024, we found, for the first time, a weak photometric variability of the nuclear activity, where the correlation between g-r color indices and g-magnitude for long-term timescale shows a BWB trend (bluer-when-brighter) with a Pearson coefficient r(g-r)=0.56, which is a medium correlation. To detect the variability of NGC 3521 during the day (IDV), we provided observations using a Zeiss-600 telescope with an aperture size of 8" at the Terskol observatory. The data obtained in the R-filter with an exposure of 90 sec for three hours on Feb 11, 2022, serve in favor of a trend towards an increase in brightness with the amplitude of variability of 0.04 +- 0.001 mag. According to the results of the simulations, the best fit to the observed SED is provided by model A, which considers the contribution to the radiation from all galaxy components, assuming that the galaxy nucleus is inactive. Within this model, we derived the stellar mass M$_{star}$ = 2.13 * 10$^{10} M_{Sun}$, the dust mass M$_{dust}$ = 8.45 * 10$^{7} M_{Sun}$, and the star formation rate SFR = 1.76 $M_{Sun}$ * yr$^{-1}$ with $χ^{2}$/d.o.f = 1.8. Also, based on the HIPASS radio data, we estimated the mass of neutral hydrogen to be M$_{HI}$ = 1.3 * 10$^{10} M_{Sun}$, which is an order of magnitude greater than the mass of the stellar component.

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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.

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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.

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arXiv2025

Discovery of the Polar Ring Galaxies with deep learning

The aim of our research is to create a catalog of strong and good candidates for PRGs using existing catalogs of PRGs, develop an image-based approach with machine learning methods for the search and discovery of PRGs in a big sky survey, and explore the capability of the CIGALE software for determining their multiwavelength properties. For the first time, we applied a deep learning method to the search for PRGs. We visually inspected galaxies from existing catalogs of PRGs to create a training sample based on high-quality SDSS images. Since the resulting training sample was extremely small (87 strong and good PRGs), we applied augmentation, image segmentation, and ensemble learning techniques. However, most effective method was transfer learning with its ability to enlarge the training sample by synthetic images generated by GALFIT. To examine deep learning approach for finding new PRGs we used the SDSS catalog of galaxies at z < 0.1. The method with synthetic images showed that even with overtraining we were able to find galaxies with a ring pattern. Our deep learning approach has resulted in the discovery of three PRGs (SDSS J140644.42+471602.0; SDSS J133650.48+492745.3; SDSS J095717.30+364953.5). Also, we visually inspected the Catalog of the SDSS Ring galaxies at z < 0.1 and discovered four PRGs among ~2,200 ring galaxies (SDSS J095851.32+320422.9; SDSS J104211.05+234448.2; SDSS J162212.63+272032.2; SDSS J104600.10+090627.2). One of the discovered galaxies with transfer learning, SDSS J140644.42+471602.0, was studied with CIGALE software to determine its spectral energy distribution in IR-UV bands. The current SFR is 71 M_sun per year, although the lack of FUV data limits this estimate. The total stellar mass is 8.34x10^{10} M_sun. The predominance of an old stellar population (two-thirds of the total mass) suggests that this PRG is undergoing interaction process.

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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.

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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↗