arXiv subjects

Alexei V. Moiseev

Publications and source records attributed to Alexei V. Moiseev.

33 records · Page 2Linked to original sources

arXiv2018

AGN photoionization of gas in companion galaxies as a probe of AGN radiation in time and direction

We consider AGN photoionization of gas in companion galaxies (cross-ionization) as a way to sample the intensity of AGN radiation in both direction and time, independent of the gas properties of the AGN host galaxies. From an initial set of 212 AGN+companion systems, identified with the help of Galaxy Zoo participants, we obtained long-slit optical spectra of 32 pairs which were a priori likely to show cross-ionization based on projected separation or angular extent of the companion. From emission-line ratios, 10 of these systems are candidates for cross-ionization, roughly the fraction expected if most AGN have ionization cones with 70-degree opening angles. Among these, Was 49 remains the strongest nearby candidate. NGC 5278/9 and UGC 6081 are dual-AGN systems with tidal debris, complicating identification of cross-ionization. The two weak AGN in the NGC 5278/9 system ionize gas filaments to a projected radius 14 kpc from each galaxy. In UGC 6081, an irregular high-ionization emission region encompasses both AGN, extending more than 15 kpc from each. The observed AGN companion galaxies with and without signs of external AGN photoionization have similar distributions in estimated incident AGN flux, suggesting that geometry of escaping radiation or long-term variability control this facet of the AGN environment. This parallels conclusions for luminous QSOs based on the proximity effect among Lyman-alpha absorbers. In some galaxies, mismatch between spectroscopic classifications in the common BPT diagram and the intensity of weaker He II and [Ne V] emission lines highlights the limits of common classifications in low-metallicity environments.

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arXiv2018

Systematic study of outflows in the Local Universe using CALIFA: I. Sample selection and main properties

We present a sample of 17 objects from the CALIFA survey where we find initial evidence of galactic winds based on their off-axis ionization properties. We identify the presence of outflows using various optical diagnostic diagrams (e.g., EW(H$α$), [Nii]/H$α$, [Sii]/H$α$, [Oi]/H$α$ line-ratio maps). We find that all 17 candidate outflow galaxies lie along the sequence of active star formation in the M$_\star$ vs. star-formation rate diagram, without a clear excess in the integrated SFR. The location of galaxies along the star-formation main sequence (SFMS) does not influence strongly the presence or not of outflows. The analysis of the star-formation rate density ($Σ_{\rm SFR}$) reveals that the CALIFA sources present higher values when compared with normal star-forming galaxies. The strength of this relation depends on the calibrator used to estimate the SFR. This excess in $Σ_{\rm SFR}$ is significant within the first effective radius supporting the idea that most outflows are driven by processes in the inner regions of a galaxy. We find that the molecular gas mass density ($Σ_\mathrm{gas}$) is a key parameter that plays an important role in the generation of outflows through its association with the local SFR. The canonical threshold reported for the generation of outflows -- $Σ_{\rm SFR}>0.1$ $\mathrm{M}_\odot \mathrm{yr}^{-1} \mathrm{kpc}^{-2}$ -- is only marginally exceeded in our sample. Within the Kennicutt-Schmidt diagram we propose a domain for galaxies hosting starburst-driven outflows defined by $Σ_{\rm SFR}>10^{-2} \,\mathrm{M}_\odot \mathrm{yr}^{-1} \mathrm{kpc}^{-2}$ and $Σ_\mathrm{gas}>10^{1.2} \, \mathrm{M}_\odot \mathrm{pc}^{-2}$ within a central kiloparcec region.

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arXiv2018

Star-formation complexes in the 'galaxy-sized' supergiant shell of the galaxy Holmberg I

We present the results of observations of the galaxy Holmberg I carried out at the Russian 6-m telescope in the narrow-band imaging, long-slit spectroscopy, and scanning Fabry-Perot interferometer modes. A detailed analysis of gas kinematics, ionization conditions, and metallicity of star-forming regions in the galaxy is presented. The aim of the paper is to analyse the propagation of star formation in the galaxy and to understand the role of the ongoing star formation in the evolution of the central 'galaxy-sized' supergiant HI shell (SGS), where all regions of star formation are observed. We show that star formation in the galaxy occurs in large unified complexes rather than in individual giant HII regions. Evidence of the triggered star formation is observed both on scales of individual complexes and of the whole galaxy. We identified two supernova-remnant candidates and one late-type WN star and analysed their spectrum and surrounding-gas kinematics. We provide arguments indicating that the SGS in Holmberg I is destructing by the influence of star formation occurring on its rims.

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arXiv2017

SCORPIO-2 Guiding and Calibration System in the Prime Focus of the 6-m Telescope

We describe a device (adapter) for off-axis guiding and photometric calibration of wide-angle spectrographs operating in the prime focus of the 6-m telescope of the Special Astrophysical Observatory of the Russian Academy of Sciences. To compensate coma in off-axis star images an achromatic lens corrector is used, which ensures maintaining image quality (FWHM) at a level of about 1'' within 15' from the optical axis. The device has two 54'-diameter movable guiding fields, which can move in 10' x 4'.5 rectangular areas. The device can perform automatic search for guiding stars, use them to control the variations of atmospheric transmittance, and focus the telescope during exposure. The limiting magnitude of potential guiding stars is mR ~17 mag. The calibration path whose optical arrangement meets the telecentrism condition allows the spectrograph to be illuminated both by a source of line spectrum (a He-Ne-Ar filled lamp) and by a source of continuum spectrum. The latter is usually represented either by a halogen lamp or a set of light-emitting diodes, which provide illumination of approximately uniform intensity over the wavelength interval from 350 to 900 nm. The adapter is used for observations with SCORPIO-2 multimode focal reducer.

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arXiv2016

The ultraluminous X-ray source HoII X-1: kinematic evidence of its escape from the cluster

We analyse the structure and kinematics of ionized gas in the vicinity of the ultraluminous X-ray source (ULX) HoII X-1 in the Holmberg II galaxy using observational data obtained with a scanning Fabry-Perot interferometer in the H$α$, [SII] and [OIII] emission lines at the Russian 6-m telescope. Decomposition of the line profiles allows us to identify the broad component of emission lines caused by the ULX action. We found evidence of an expanding superbubble around the young star cluster located in the studied region. We conclude that the blue-shifted 'arc' around the ULX observed in the line-of-sight velocity field may correspond to a bow shock caused by the ULX movement from that nearby young star cluster. If this interpretation is correct, it will be the first kinematic evidence of ULX's escape from their parent star clusters.

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arXiv2016

Complexes of triggered star formation in supergiant shell of Holmberg II

We report a detailed analysis of all regions of current star formation in the walls of the supergiant HI shell (SGS) in the galaxy Holmberg II based on observations with a scanning Fabry-Perot interferometer at the 6-m SAO RAS telescope. We compare the structure and kinematics of ionized gas with that of atomic hydrogen and with the stellar population of the SGS. Our deep H$α$ images and archival images taken by the HST demonstrate that current star formation episodes are larger and more complicated than previously thought: they represent unified star-forming complexes with sizes of several hundred pc rather than 'chains' of separate bright nebulae in the walls of the SGS. The fact that we are dealing with unified complexes is evidenced by identified faint shell-like structures of ionized and neutral gas which connect several distinct bright HII regions. Formation of such complexes is due to the feedback of stars with very inhomogeneous ambient gas in the walls of the SGS. The arguments supporting an idea about the triggering of star formation in SGS by the HI supershells collision are presented. We also found a faint ionized supershell inside the HI SGS expanding with a velocity of no greater than 10-15 km/s. Five OB stars located inside the inner supershell are sufficient to account for its radiation, although a possibility of leakage of ionizing photons from bright HII regions is not ruled out as well.

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arXiv2016

Galaxies with conspicuous optical warps

In this paper, we present results of a photometric and kinematic study for a sample of 13 edge-on spiral galaxies with pronounced integral-shape warps of their stellar discs. The global structure of the galaxies is analyzed on the basis of the Sloan Digital Sky Survey (SDSS) imaging, in the g, r and i passbands. Spectroscopic observations are obtained with the 6-m Special Astrophysical Observatory telescope. In general, galaxies of the sample are typical bright spiral galaxies satisfying the Tully-Fisher relation. Most of the galaxies reside in dense spatial environments and, therefore, tidal encounters are the most probable mechanism for generating their stellar warps. We carried out a detailed analysis of the galaxies and their warps and obtained the following main results: (i) maximum angles of stellar warps in our sample are about 20°; (ii) warps start, on average, between 2 and 3 exponential scale lengths of a disc; (iii) stronger warps start closer to the center, weak warps start farther; (iv) warps are asymmetric, with the typical degree of asymmetry of about several degrees (warp angle); (v) massive dark halo is likely to preclude the formation of strong and asymmetric warps.

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arXiv2016

First results of the Kourovka Planet Search: discovery of transiting exoplanet candidates in the first three target fields

We present the first results of our search for transiting exoplanet candidates as part of the Kourovka Planet Search (KPS) project. The primary objective of the project is to search for new hot Jupiters which transit their host stars, mainly in the Galactic plane, in the $R_c$ magnitude range of 11 to 14 mag. Our observations were performed with the telescope of the MASTER robotic network, installed at the Kourovka astronomical observatory of the Ural Federal University (Russia), and the Rowe-Ackermann Schmidt Astrograph, installed at the private Acton Sky Portal Observatory (USA). As test observations, we observed three celestial fields of size $2\times2$ deg$^2$ during the period from 2012 to 2015. As a result, we discovered four transiting exoplanet candidates among the 39000 stars of the input catalogue. In this paper, we provide the description of the project and analyse additional photometric, spectral, and speckle interferometric observations of the discovered transiting exoplanet candidates. Three of the four transiting exoplanet candidates are most likely astrophysical false positives, while the nature of the fourth (most promising) candidate remains to be ascertained. Also, we propose an alternative observing strategy that could increase the project's exoplanet haul.

astro-ph.EP↗

arXiv2016

Imaging and spectroscopic observations of a strange elliptical bubble in the northern arm of the spiral galaxy NGC 6946

NGC 6946, known as the Fireworks galaxy because of its high supernova rate and high star formation, is embedded in a very extended HI halo. Its northern spiral arm is well detached from the galactic main body. We found that this arm contains a large (~300 pc in size) Red Ellipse, named according to a strong contamination of the H-alpha emission line on its optical images. The ellipse is accompanied by a short parallel arc and a few others still smaller and less regular; a bright star cluster is seen inside these features. The complicated combination of arcs seems to be unique, it is only a bit similar to some SNRs. However, the long-slit spectral data obtained with the Russian 6-m telescope did not confirm the origin of the nebula as a result of a single SN outburst. The emission-line spectrum corresponds to the photoionization by young hot stars with a small contribution of shock ionization. The most likely explanation of the Red Ellipse is a superbbuble created by a collective feedback of massive stars in the star cluster located in the NE side of the Red Ellipse. However, the very regular elliptical shape of the nebulae seems strange.

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arXiv2015

What controls the ionized gas turbulent motions in dwarf galaxies?

Using 3D spectroscopy with a scanning Fabry-Perot interferometer, we study the ionized gas kinematics in 59 nearby dwarf galaxies. Combining our results with data from literature, we provide a global relation between the gas velocity dispersion (sigma) and the star formation rate (SFR) and Hαluminosity for galaxies in a very broad range of star formation rates SFR=0.001-300 Msun/yr. We find that the SFR-sigma relation for the combined sample of dwarf galaxies, star forming, local luminous, and ultra-luminous infrared galaxies can be fitted as sigma~ SFR^(5.3+-0.2). This implies that the slope of the L-sigma relation inferred from the sample of rotation supported disc galaxies (including mergers) is similar to the L-sigma relation of individual giant HII regions. We present arguments that the velocity dispersion of the ionized gas does not reflect the virial motions in the gravitational potential of dwarf galaxies, and instead is mainly determined by the energy injected into the interstellar medium by the ongoing star formation.

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arXiv2014

Ionized gas velocity dispersion and multiple supernova explosions

Using 3D numerical simulations we study the evolution of the H$α$ intensity and velocity dispersion for single and multiple supenova (SN) explosions. We find that the $I_{\rm Hα}-σ$ diagram obtained for simulated gas flows is similar in shape to that observed in dwarf galaxies. We conclude that colliding SN shells with significant difference in age are resposible for high velocity dispersion that reaches values high as $\simgt 100$kms$^{-1}$. Such a high velocity dispersion could be hardly got for a single SN remnant. Peaks of velocity dispersion on the $I_{\rm Hα}-σ$ diagram may correspond to several stand-alone or merged SN remnants with moderately different ages. The procedure of the spatial resolution degrading in the H$α$ intensity and velocity dispersion maps makes the simulated $I_{\rm Hα}-σ$ diagrams close to those observed in dwarf galaxies not only in shape, but also quantitatively.

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arXiv2014

Inner polar gaseous disks: incidence, ages, possible origin

We review our current knowledge about a particular case of decoupled gas kinematics -- inner ionized-gas polar disks. Though more difficult to be noticed, they seem to be more numerous than their large-scale counterparts; our recent estimates imply about 10 per cent of early-type disk galaxies to be hosts of inner polar disks. Since in the most cases the kinematics of the inner polar gaseous disks is decoupled from the kinematics of the outer large-scale gaseous disks and since they nested around very old stellar nuclei, we speculate that the inner polar disks may be relics of very early events of external gas accretion several Gyr ago. Such view is in agreement with our new paradigm of the disk galaxies evolution.

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arXiv2011

Stars and ionized gas in S0 galaxy NGC 7743: an inclined large-scale gaseous disk

We used deep long-slit spectra and integral-field spectral data to study the stars and ionized gas kinematics and stellar population properties in the lenticular barred galaxy NGC 7743. We have shown that ionized gas at the distances larger than 1.5 kpc from the nucleus settles in the disk which is significantly inclined to the stellar disk of the galaxy. Making different assumptions about the geometry of the disks and involving different sets of emission lines into the fitting, under the assumption of thin flat disk circular rotation, we obtain the full possible range of angle between the disks to be 34+/-9 or 77+/-9 deg. The most probable origin of the inclined disk is the external gas accretion from a satellite, orbiting the host galaxy with a corresponding angular momentum direction. The published data on the HI distribution around NGC 7743 suggest that the galaxy has a gas-rich environment. The emission-line ratio diagrams imply the domination of shock waves in the ionization state of the gaseous disk, whereas the contribution of photoionization by recent star formation seems to be negligible. In some parts of the disk a difference between the velocities of the gas emitting in the forbidden lines and in the Balmer lines is detected. It may be caused by the fact that the inclined disk is mainly shock-excited, whereas some fraction of the Balmer-line emission is produced by a small amount of gas excited by young stars in the main stellar disk of NGC 7743. In the circumnuclear region (R< 200 pc) some evidences of the AGN jet interaction with an ambient interstellar medium were found.

astro-ph.CO↗

arXiv2010

Structure of the Galaxies in the NGC 80 Group

BV-bands photometric data obtained at the 6-m telescope of the Special Astrophysical Observatory are used to analyze the structure of 13 large disk galaxies in the NGC 80 group. Nine of the 13 galaxies under consideration are classified by us as lenticular galaxies. The stellar populations in the galaxies are very different, from old ones with ages of T>10 Gyrs (IC 1541) to relatively young, with the ages of T<2-3 Gyr (IC 1548, NGC 85). In one case, current star formation is known (UCM 0018+2216). In most of the galaxies, more precisely in all of them more luminous than M(B) -18, two-tiered (`antitruncated') stellar disks are detected, whose radial surface brightness profiles can be fitted by two exponential segments with different scalelengths -- shorter near the center and longer at the periphery. All dwarf S0 galaxies with single-scalelength exponential disks are close companions to giant galaxies. Except for this fact, no dependence of the properties of S0 galaxies on distance from the center of the group is found. Morphological traces of minor merger are found in the lenticular galaxy NGC 85. Basing on the last two points, we conclude that the most probable mechanisms for the transformation of spirals into lenticular galaxies in groups are gravitational ones, namely, minor mergers and tidal interactions.

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arXiv2007

3D Spectroscopy of Blue Compact Galaxies. Diagnostic Diagrams

Here we present the analysis of 3D spectroscopic data of three Blue Compact Galaxies (Mrk324, Mrk370, and IIIZw102). Each of the more than 22500 spectra obtained for each galaxy has been fitted by a single gaussian from which we have inferred the velocity dispersion (sigma), the peak intensity (Ipeak), and the central wavelength (lambda_c). The analysis shows that the sigma vs Ipeak diagrams look remarkably similar to those obtained for giant extragalactic HII regions. They all present a supersonic narrow horizontal band that extends across all the range of intensities and that result from the massive nuclear star-forming regions of every galaxy. The sigma vs Ipeak diagrams present also several inclined bands of lower intensity and an even larger sigma, arising from the large galactic volumes that surround the main central emitting knots. Here we also show that the sigma vs lambda_c and lambda_c vs Ipeak diagrams, are powerful tools able to unveil the presence of high and low mass stellar clusters, and thus allow for the possibility of inferring the star formation activity of distant galaxies, even if these are not spatially resolved.

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