arXiv subjects

A. Moiseev

Publications and source records attributed to A. Moiseev.

At least 19 recordsLinked to original sources

arXiv2026

Spectroscopic galaxy redshifts in the Peanut cluster -- a massive nearly head-on cluster merger shortly after pericenter passage

The Peanut cluster (SRGe J023820.8+200556, SRGe CL0238.3+2005, $z_{spec}$ = 0.42) has recently emerged as a candidate for a rare, massive merger, potentially analogous to the Bullet cluster. We present the results of optical identification and spectroscopic redshift measurements for 31 galaxies in the Peanut cluster, including 26 new redshifts obtained with the 6-m telescope BTA (Big Telescope Alt-azimuthal) at SAO RAS between October 2024 and January 2025. The derived distribution of line-of-sight velocities reveals the possible presence of two subclusters with a line-of-sight velocity difference of ~2000 km/s. However, statistical tests and the Dressler-Schectman test show that the hypothesis that the observed velocity distribution can be described by a normal distribution for a single cluster cannot be ruled out, and the evidence for the existence of two gravitationally bound substructures remains ambiguous. Assuming a single cluster with the normal velocity distribution, the estimated galaxy velocity dispersion is $\sigma_{los} = 1455 \pm 83$ km/s, corresponding to the total cluster mass of $M_{200} = 2 \times 10^{15} M_\odot$ based on the mass-velocity dispersion scaling relation. In either scenario -- a single extremely massive cluster or an ongoing merger -- the Peanut cluster appears to be a very rare and peculiar object, comparable to such extreme systems as the Bullet cluster (1E 0657-56) or El Gordo (ACT-CL J0102-4915).

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arXiv2025

Green Bean galaxies and the fading echoes of AGN activity

Green Bean is a rare type of galaxy which represents a short-lived phase in the life cycle of active galactic nuclei (AGN), characterised by large-scale, powerful ionised clouds in the circumgalactic medium. Recent studies demonstrate that these extended ionised structures may reflect fading signatures of past AGN activity, often manifested in the form of large-scale ionisation cones. The analysis of their observational properties provides unique constraints on AGN lifetimes, feedback mechanisms, and transitions between radiative and kinetic modes of activity. In this paper we announce the first results of the project dedicated to the long-slit spectroscopic and scanning Fabry-Perot interferometric observations of Green Bean galaxies at the Russian 6-m telescope with SCORPIO-2 multi-mode instrument. We describe the data reduction and spectral fitting procedures that allow one to characterise ionisation conditions in extended gaseous regions of the galaxy SDSSJ095100.54+051026.7.

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arXiv2024

Discovery and characterisation of a new Galactic Planetary Nebula

Planetary nebulae are one of the final stages in the evolution of low and intermediate mass stars. They occur in a variety of shapes. Older and fainter ones are generally more difficult to identify because of the lower surface brightness. This paper reports the serendipitous discovery of a new faint Galactic planetary nebula (PN), during a campaign to identify dwarf galaxies, companions of the spiral galaxy NGC 2403. We aim at confirming the nature as PN of a diffuse object identified in the Camelopardalis constellation. We obtained narrow-band filter images and spectra of the nebula and its central star with amateur and professional telescopes having diameters from 20 cm to 6 m. We detected a dense triangular nebula, surrounded by an elliptical region, named Cam nebula. They are part of a larger and fainter circular nebular structure, named TBG-1, at the centre of which we have identified the possible central star, a white dwarf with a temperature of about 22 000 K. The analysis of the spectrum made it possible to measure the physical characteristics of the nebula, in particular its electronic density and temperature. Analysis of the images, of the spectra of the nebula and of the central star confirm the PN nature of TBG-1, located at the distance of about 1 kpc. This work reaffirms the potential for fruitful collaborations between astronomers and amateur astronomers in the detection and study of new objects.

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arXiv2022

Star Formation in Outer Rings of S0 galaxies. V. UGC 4599 -- an S0 with gas probably accreted from a filament

Though S0 galaxies are usually thought to be `red and dead', they often demonstrate weak star formation organised in ring structures and located in their outer disks. We try to clarify the nature of this phenomenon and its difference from star formation in spiral galaxies. The moderate-luminosity nearby S0 galaxy, UGC 4599, is studied here. By applying long-slit spectroscopy at the Russian 6m telescope, we have measured stellar kinematics for the main body of the galaxy and strong emission-line flux ratios in the ring. After inspecting the gas excitation in the ring using line ratio diagrams and having shown that it is ionized by young stars, we have determined the gas oxygen abundance by using conventional strong-line calibration methods. We have inspected the gas kinematics in the ring with Fabry-Perot interferometer data obtained at the William Herschel Telescope. The pattern and properties of the brightest star formation regions are studied with the tunable filter MaNGaL at the 2.5m telescope of the Caucasian Mountain Observatory of the Sternberg Astronomical Institute (CMO SAI MSU). The gas metallicity in the ring is certainly subsolar, [O/H]$=-0.4 \pm 0.1$~dex, that is different from the majority of the outer starforming rings in S0s studied by us which have typically nearly solar metallicity. The total stellar component of the galaxy which is old in the center is less massive than its extended gaseous disk. We conclude that probably the ring and the outer disk of UGC~4599 are a result of gas accretion from a cosmological filament.

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arXiv2022

Search for LBVs in the Local Volume galaxies: study of two stars in NGC 1156

We continue the search for luminous blue variables (LBVs) in Local Volume galaxies in order to study their fundamental parameters. In this paper, we report the discovery of two new LBVs in the dwarf irregular galaxy NGC 1156. Both stars exhibit spectral variability simultaneously with strong brightness variations: $\Delta \text{R}_c = 0.84 \pm 0.23^m$ for J025941.21+251412.2 and $\Delta \text{R}_c = 2.59 \pm 0.10^m$ for J025941.54+251421.8. The bolometric luminosities of the stars are in the range of L$_\text{Bol} \approx (0.8 - 1.6) \times 10^6$ L$_\odot$. These values are corrected for reddening A$_\text{V} \approx 0.9$ and are given for the distance to the galaxy D=7.0$\pm$0.4 Mpc, which we have measured by the TRGB method. Both stars are above the Humphreys-Davidson limit in the region of relatively low temperatures, T$_\text{eff} \lesssim 10$ kK on the temperature-luminosity diagram. J025941.54+251421.8 had a temperature below the hydrogen ionisation threshold at maximum brightness, exhibiting behaviour very similar to that of the known LBV R71 during its 2012 outburst. We have estimated the masses of the detected LBVs and studied the properties of their stellar environment. We discuss our results within the framework of both a single star and a binary system evolution scenario for LBVs.

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arXiv2022

Follow-Up of Extended Shells around B[e] Stars

B[e] stars are massive B type emission line stars in different evolutionary stages ranging from pre-main sequence to post-main sequence. Due to their mass loss and ejection events these objects deposit huge amounts of mass and energy into their environment and enrich it with chemically processed material, contributing significantly to the chemical and dynamical evolution of their host galaxies. However, the large-scale environments of these enigmatic objects have not attracted much attention. The first and so far only catalog reporting the detection of extended shells around a sample of B[e] stars was an Ha imaging survey carried out in the year 2001, and was limited to bright targets in the northern hemisphere. We have recently started a follow-up of those targets to detect possible evolution of their nebulae in the plane of the sky over a baseline of two decades. Furthermore, we extend our survey to southern targets and fainter northern ones to complement and complete our knowledge on large-scale ejecta surrounding B[e] stars. Besides imaging in Ha and selected nebular lines, we utilize long-slit and 3D spectral observations across the nebulae to derive their physical properties. We discovered pronounced nebula structures around 15 more objects, resulting in a total of 27 B[e] stars with a large-scale nebula. Here we present our (preliminary) results for three selected objects: the two massive supergiants MWC137 and MWC 314, and the unclassified B[e] star MWC 819.

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arXiv2019

Star formation in outer rings of S0 galaxies. II. NGC 4513 -- a multi-spin ringed S0 galaxy

Though S0 galaxies are usually thought to be `red and dead', they demonstrate often star formation organized in ring structures. We try to clarify the nature of this phenomenon and its difference from star formation in spiral galaxies. The moderate-luminosity nearby S0 galaxy, NGC 4513, is studied here. By applying long-slit spectroscopy along the major axis of NGC 4513, we have measured gas and star kinematics, Lick indices for the main body of the galaxy, and strong emission-line flux ratios in the ring. After inspecting the gas excitation in the ring using the line ratios diagnostic diagrams and have assured that it is ionized by young stars, we have determined the gas oxygen abundance by using popular strong-line calibration methods. We have estimated star formation rate (SFR) in the outer ring by using the archival Galaxy Evolution Explorer (GALEX) ultraviolet images of the galaxy. The ionized gas counterrotates the stars over the whole extension of NGC 4513 so being accreted from outside. The gas metallicity in the ring is slightly subsolar, [O/H]=-0.2 dex, matching the metallicity of the stellar component of the main galactic disc. However the stellar component of the ring is much more massive than can be explained by the current star formation level in the ring. We conclude that probably the ring of NGC 4513 is a result of tidal disruption of a massive gas-rich satellite, or it may be a consequence of a long star-formation event provoked by a gas accretion from a cosmological filament having started some 3 Gyr ago.

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arXiv2019

Spectroscopy and polarimetry of the gravitationally lensed quasar SDSS J1004+4112 with the 6m SAO RAS telescope

We present new spectroscopic and polarimetric observations of the gravitational lens SDSS J1004+4112 taken with the 6m telescope of the Special Astrophysical Observatory (SAO, Russia). In order to explain the variability that is observed only in the blue wing of the C IV emission line, corresponding to image A, we analyze the spectroscopy and polarimetry of the four images of the lensed system. Spectra of the four images were taken in 2007, 2008, and 2018, and polarization was measured in the period 2014-2017. Additionally, we modeled the microlensing effect in the polarized light, assuming that the source of polarization is the equatorial scattering in the inner part of the torus. We find that a blue enhancement in the CIV line wings affects component A in all three epochs. We also find that the UV continuum of component D was amplified in the period 2007-2008, and that the red wings of CIII] and CIV appear brighter in D than in the other three components. We report significant changes in the polarization parameters of image D, which can be explained by microlensing.Our simulations of microlensing of an equatorial scattering region in the dusty torus can qualitatively explain the observed changes in the polarization degree and angle of image D. We do not detect significant variability in the polarization parameters of the other images (A, B, and C), although the averaged values of the polarization degree and angle are different for the different images. Microlensing of a broad line region model including a compact outflowing component can qualitatively explain the CIV blue wing enhancement (and variation) in component A. However, to confirmed this hypothesis, we need additional spectroscopic observation in future.

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arXiv2019

Revealing the nature of central emission nebulae in the dwarf galaxy NGC 185

In this paper we present new optical observations of the galaxy NGC 185 intended to reveal the status of supernova remnants (SNRs) in this dwarf companion of the Andromeda galaxy. Previously, it was reported that this galaxy hosts one SNR. Our deep photometric study with the 2m telescope at Rozhen National Astronomical Observatory using narrow-band H$α$ and [SII] filters revealed complex structure of the interstellar medium in the center of the galaxy. To confirm the classification and to study the kinematics of the detected nebulae, we carried out spectroscopic observations using the SCORPIO multi-mode spectrograph at the 6m telescope at the Special Astrophysical Observatory of the Russian Academy of Science, both in low- and high-resolution modes. We also searched the archival X-ray and radio data for counterparts of the candidate SNRs identified by our optical observations. Our observations imply the presence of one more SNR, one possible HII region previously cataloged as part of an SNR, and the presence of an additional source of shock ionization in one low-brightness PN. We detected enhanced [SII]/H_alpha and [NII]/H_alpha line ratios, as well as relatively high (up to 90 km s$^{-1}$) expansion velocities of the two observed nebulae, motivating their classification as SNRs (with diameters of 45 pc and 50 pc), confirmed by both photometric and spectral observations. The estimated electron density of emission nebulae is 30 - 200 cm$^{-3}$. Archival XMM-Newton observations indicate the presence of an extended, low-brightness, soft source in projection of one of the optical SNRs, whereas the archival VLA radio image shows weak, unresolved emission in the center of NGC 185.

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arXiv2019

The X-ray-Resolved Supernova Remnant S8 in the Dwarf Irregular Galaxy IC 1613

We conducted an observation of the nearby irregular galaxy IC 1613 with the Chandra X-ray Observatory using the S3 chip of the ACIS with an effective exposure time of 49.9 ksec. The observation primarily targeted the extensive bubble and star formation region in the northeast quadrant of the galaxy. The only known supernova remnant (SNR) in IC 1613, S8, is also the galaxy's most luminous X-ray source (L_X (0.3-8 keV) ~5-6x10^{36} erg/s). We resolve the SNR with Chandra and compare its nearly circular X-ray morphology with Halpha and radio images. We assign an upper limit on the luminosity of any possible associated compact central object of ~4x10^{35}$ erg/s (0.3-8 keV band) and conclude that we would detect a Crab-like pulsar but not a Cas A-like object. We infer an age for S8 of ~3400-5600 years and compare it to other SNRs in the Local Group. We suggest that S8 is a young composite SNR.

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arXiv2019

Neutrinos, Cosmic Rays and the MeV Band

The possible association of the blazar TXS 0506+056 with a high-energy neutrino detected by IceCube holds the tantalizing potential to answer three astrophysical questions: 1. Where do high-energy neutrinos originate? 2. Where are cosmic rays produced and accelerated? 3. What radiation mechanisms produce the high-energy γ-rays in blazars? The MeV gamma-ray band holds the key to these questions, because it is an excellent proxy for photo-hadronic processes in blazar jets, which also produce neutrino counterparts. Variability in MeV gamma-rays sheds light on the physical conditions and mechanisms that take place in the particle acceleration sites in blazar jets. In addition, hadronic blazar models also predict a high level of polarization fraction in the MeV band, which can unambiguously distinguish the radiation mechanism. Future MeV missions with a large field of view, high sensitivity, and polarization capabilities will play a central role in multi-messenger astronomy, since pointed, high-resolution telescopes will follow neutrino alerts only when triggered by an all-sky instrument.

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arXiv2019

High-Energy Polarimetry - a new window to probe extreme physics in AGN jets

The constantly improving sensitivity of ground-based and space-borne observatories has made possible the detection of high-energy emission (X-rays and gamma-rays) from several thousands of extragalactic sources. Enormous progress has been made in measuring the continuum flux enabling us to perform imaging, spectral and timing studies. An important remaining challenge for high-energy astronomy is measuring polarization. The capability to measure polarization is being realized currently at X-ray energies (e.g. with IXPE), and sensitive gamma-ray telescopes capable of measuring polarization, such as AMEGO, AdEPT, e-ASTROGAM, etc., are being developed. These future gamma-ray telescopes will probe the radiation mechanisms and magnetic fields of relativistic jets from active galactic nuclei at spatial scales much smaller than the angular resolution achieved with continuum observations of the instrument. In this white paper, we discuss the scientific potentials of high-energy polarimetry, especially gamma-ray polarimetry, including the theoretical implications, and observational technology advances being made. In particular, we will explore the primary scientific opportunities and wealth of information expected from synergy of multi-wavelength polarimetry that will be brought to multi-messenger astronomy.

astro-ph.HE↗

arXiv2018

The e-ASTROGAM gamma-ray space observatory for the multimessenger astronomy of the 2030s

e-ASTROGAM is a concept for a breakthrough observatory space mission carrying a gamma-ray telescope dedicated to the study of the non-thermal Universe in the photon energy range from 0.15 MeV to 3 GeV. The lower energy limit can be pushed down to energies as low as 30 keV for gamma-ray burst detection with the calorimeter. The mission is based on an advanced space-proven detector technology, with unprecedented sensitivity, angular and energy resolution, combined with remarkable polarimetric capability. Thanks to its performance in the MeV-GeV domain, substantially improving its predecessors, e-ASTROGAM will open a new window on the non-thermal Universe, making pioneering observations of the most powerful Galactic and extragalactic sources, elucidating the nature of their relativistic outflows and their effects on the surroundings. With a line sensitivity in the MeV energy range one to two orders of magnitude better than previous and current generation instruments, e-ASTROGAM will determine the origin of key isotopes fundamental for the understanding of supernova explosion and the chemical evolution of our Galaxy. The mission will be a major player of the multiwavelength, multimessenger time-domain astronomy of the 2030s, and provide unique data of significant interest to a broad astronomical community, complementary to powerful observatories such as LISA, LIGO, Virgo, KAGRA, the Einstein Telescope and the Cosmic Explorer, IceCube-Gen2 and KM3NeT, SKA, ALMA, JWST, E-ELT, LSST, Athena, and the Cherenkov Telescope Array.

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arXiv2015

The Third Catalog of Active Galactic Nuclei Detected by the Fermi Large Area Telescope

The third catalog of active galactic nuclei (AGNs) detected by the Fermi-LAT (3LAC) is presented. It is based on the third Fermi-LAT catalog (3FGL) of sources detected between 100 MeV and 300 GeV with a Test Statistic (TS) greater than 25, between 2008 August 4 and 2012 July 31. The 3LAC includes 1591 AGNs located at high Galactic latitudes (|b|>10°), a 71% increase over the second catalog based on 2 years of data. There are 28 duplicate associations, thus 1563 of the 2192 high-latitude gamma-ray sources of the 3FGL catalog are AGNs. Most of them (98%) are blazars. About half of the newly detected blazars are of unknown type, i.e., they lack spectroscopic information of sufficient quality to determine the strength of their emission lines. Based on their gamma-ray spectral properties, these sources are evenly split between flat-spectrum radio quasars (FSRQs) and BL~Lacs. The most abundant detected BL~Lacs are of the high-synchrotron-peaked (HSP) type. About 50% of the BL~Lacs have no measured redshifts. A few new rare outliers (HSP-FSRQs and high-luminosity HSP BL~Lacs) are reported. The general properties of the 3LAC sample confirm previous findings from earlier catalogs. The fraction of 3LAC blazars in the total population of blazars listed in BZCAT remains non-negligible even at the faint ends of the BZCAT-blazar radio, optical and X-ray flux distributions, which is a clue that even the faintest known blazars could eventually shine in gamma rays at LAT-detection levels. The energy-flux distributions of the different blazar populations are in good agreement with extrapolation from earlier catalogs.

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arXiv2015

Polarimetric and Spectroscopic Observations of a Dynamically New Comet C/2012 J1 (Catalina)

We present the analysis of the polarimetric and spectral data obtained for the dynamically new comet C/2012\,J1 (Catalina) when it was at a distance of 3.17~AU from the Sun. The observations were made at the prime focus of the 6-m BTA telescope using the SCORPIO-2 focal reducer. The map of the distribution of linear polarization in the cometary coma was constructed. The calculated value of linear polarization was on average about $-2\%$. Spectral analysis of the cometary coma allowed us to detect the emission of the CN molecule in the (0--0) band. The gas production rate was derived using the Haser model and amounted to $3.7\times10^{23}$~molecules per second.

astro-ph.EP↗

arXiv2014

Structure and kinematics of the polar ring galaxies: new observations and estimation of the dark halo shape

The polar ring galaxies (PRGs) represent an interesting type of peculiar systems in which the outer matter is rotating in the plane which is roughly perpendicular to the disk of the main galaxy. Despite the long lasting study of the PRGs there is a lack of the detailed enough observational data, there are still many open questions. Among the most interesting issues there are the estimate of the flattening of the dark matter halos in these systems and the verification of the assumption that the most massive polar structures were formed by the accretion of the matter from the intergalactic filaments. The new catalog recently collected by our team using the SDSS images increased by several times the number of known PRGs. The current paper gives the overview of our latest results on the study of morphological and photometric structure of the PRGs. Using the stellar and ionized gas kinematics data based on spectral observations with the Russian 6-m telescope we estimate the dark matter halo shape in the individual galaxies.

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arXiv2014

Stellar kinematics of X-ray bright massive elliptical galaxies

We discuss a simple and fast method for estimating masses of early-type galaxies from optical data and compare the results with X-ray derived masses. The optical method relies only on the most basic observables such as the surface brightness $I(R)$ and the line-of-sight velocity dispersion $σ_p(R)$ profiles and provides an anisotropy-independent estimate of the galaxy circular speed $V_c$. The mass-anisotropy degeneracy is effectively overcome by evaluating $V_c$ at a characteristic radius $R_{\rm sweet}$ defined from {\it local} properties of observed profiles. The sweet radius $R_{\rm sweet}$ is expected to lie close to $R_2$, where $I(R) \propto R^{-2}$, and not far from the effective radius $R_{\rm eff}$. We apply the method to a sample of five X-ray bright elliptical galaxies observed with the 6-m telescope BTA-6 in Russia. We then compare the optical $V_c$-estimate with the X-ray derived value, and discuss possible constraints on the non-thermal pressure in the hot gas and configuration of stellar orbits. We find that the average ratio of the optical $V_c$-estimate to the X-ray one is equal to $\approx 0.98$ with $11 \%$ scatter, i.e. there is no evidence for the large non-thermal pressure contribution in the gas at $\sim R_{\rm sweet}$. From analysis of the Lick indices H$β$, Mgb, Fe5270 and Fe5335, we calculate the mass of the stellar component within the sweet radius. We conclude that a typical dark matter fraction inside $R_{\rm sweet}$ in the sample galaxies is $\sim 60\%$ for the Salpeter IMF and $\sim 75 \%$ for the Kroupa IMF.

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arXiv2011

Looking inside the nest: the hidden structure of the merger galaxy NGC 1316 (Fornax A)

We present an analysis of the circumnuclear structure of NGC 1316 using both near-infrared imaging and stellar kinematics. 2D decomposition of the images suggests the presence of a structure that resembles inner gaseous spiral arms, at about 5 to 15" from the center (500 to 1500 pc). We also find a disc-like stellar structure with radius less than 200 pc. Analysis of previously published SINFONI integral field kinematics data indicates a kinematically decoupled core in the same spatial scale, further evidence that indeed the nuclear stellar structure found is a kinematically cold stellar disc. We suggest that both newly-found structural components are the result of a recent accretion of a companion galaxy.

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