arXiv subjects

A. V. Moiseev

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

At least 109 records · Page 6Linked to original sources

arXiv2003

The phenomenon of the galaxy NGC 6286: a forming polar ring or a superwind?

(abridged)We present the observations of the pair of interacting galaxies NGC6285/86 carried out with the 6m SAO RAS telescope by using 1D and 2D spectroscopy. The observations of NGC6286 with a long-slit spectrograph (UAGS) near the H-alpha line revealed the rotation of the gaseous disk around an axis offset by 5''-7'' from the photometric center and a luminous gas at a distance up to 9 kpc in a direction perpendicular to the galactic plane. Using a multipupil fiber spectrograph (MPFS), we constructed the velocity fields of the stellar and gaseous components in the central region of this galaxy, which proved to be similar. The similar line-of-sight velocities of the pair and the wide (5'x 5') field of view of the scanning Fabry-Perot interferometer (IFP) allowed us to obtain images in the H-alpha and [NII]6583 emission lines and in the continuum as well as to construct the line-of-sight velocity fields and to map the distribution of the [NII]6583/H-alpha ratio for both galaxies simultaneously. Based on these data, we studied the gas kinematics in the galaxies, constructed their rotation curves, and estimated their masses. We found no evidence of gas rotation around the major axis of NGC6286, which argues against the assumption that this galaxy has a forming polar ring. The IFP observations revealed an emission nebula around this galaxy with a structure characteristic for superwind galaxies. The large [NII]6583/H-alpha ratio, which suggests the collisional excitation of its emission, and the high infrared luminosity are additional arguments for the hypothesis of a superwind in the galaxy NGC 6286. A close encounter of the two galaxies was probably responsible for the starburst and the bipolar outflow of hot gas from the central region of the disk.

astro-ph↗

arXiv2003

The Leo I Cloud: Secular nuclear evolution of NGC 3379, NGC 3384, and NGC 3368?

The central regions of the three brightest members of the Leo I galaxy group -- NGC 3368, NGC 3379, and NGC 3384 -- are investigated by means of 2D spectroscopy. In all three galaxies we have found separate circumnuclear stellar and gaseous subsystems -- more probably, disks -- whose spatial orientations and spins are connected to the spatial orientation of the supergiant intergalactic HI ring reported previously by Schneider et al. (1983) and Schneider (1985, 1989). In NGC 3368 the global gaseous disk seems also to be inclined to the symmetry plane of the stellar body, being probably of external origin. Although the rather young mean stellar age and spatial orientations of the circumnuclear disks in NGC 3379, NGC 3384, and NGC 3368 could imply their recent formation from material of the intergalactic HI cloud, the time scale of these secondary formation events, of order 3 Gyr, does not support the collision scenario of Rood & Williams (1985), but is rather in line with the ideas of Schneider (1985, 1989) regarding tidal interactions of the galaxies with the HI cloud on timescales of the intergroup orbital motions.

astro-ph↗

arXiv2003

Detailed Kinematic Study of the Ionized and Neutral Gas in the Complex of Star Formation in the Galaxy IC 1613

We carried out detailed kinematic studies of the complex of multiple HI and HII shells that represent the only region of ongoing star formation in the dwarf irregular galaxy IC 1613. We investigated the ionized-gas kinematics by using Fabry--Perot H-alpha observations with the 6-m Special Astrophysical Observatory telescope and the neutral-gas kinematics by using VLA 21-cm radio observations. We identified three extended (300-350 pc) neutral shells with which the brightest HII shells in the complex of star formation are associated. The neutral-gas kinematics in the complex has been studied for the first time and the H~I shells were found to expand at a velocity of 15--18 km/s. We constructed velocity ellipses for all HII shells in the complex and refined (increased) the expansion velocities of most of them. The nature of the interacting ionized and neutral shells is discussed.

astro-ph↗

arXiv2002

Application of the global modal approach to the spiral galaxies

We have tested the applicability of the global modal approach in the density wave theory of spiral structure for a sample of spiral galaxies with measured axisymmetric background properties. We report here the results of the simulations for four galaxies: NGC 488, NGC 628, NGC 1566, and NGC 3938. Using the observed radial distributions for the stellar velocity dispersions and the rotation velocities we have constructed the equilibrium models for the galactic disks in each galaxy and implemented two kinds of stability analyses - the linear global analysis and 2D-nonlinear simulations. In general, the global modal approach is able to reproduce the observed properties of the spiral arms in the galactic disks. The growth of spirals in the galactic disks can be physically understood in terms of amplification by over-reflection at the corotation resonance. Our results support the global modal approach as a theoretical explanation of spiral structure in galaxies.

astro-ph↗

arXiv2002

Reduction of CCD observations with scanning Fabry-Perot interferometer

The algorithms used for reduction of data obtained in a Fabry-Perot interferometer mode of the new focal reducer of the 6m telescope SCORPIO are described. The main attention is focused on the procedures of photometry correction of channels and night sky emission subtraction, which is especially important for observations with a CCD in comparison with a photon counter. The influence of various sources of errors on measurements of radial velocities in a data cube is investigated. Examples of velocity field construction by using emission lines in the galaxy NGC 6951 and absorption lines in the globular cluster M 71 are presented.

astro-ph↗

arXiv2002

Two-dimensional spectroscopy of double-barred galaxies

We describe the results of our spectroscopy for a sample of barred galaxies whose inner regions exhibit an isophotal twist commonly called a secondary bar. The line-of-sight velocity fields of the ionized gas and stars and the light-of-sight velocity dispersion fields of the stars were constructed from two-dimensional spectroscopy with the 6m Special Astrophysical Observatory telescope. We detected various types of non-circular motions of ionized gas: radial flows within large-scale bars, counter-rotation of the gas and stars at the center of NGC 3945, a polar gaseous disk in NGC 5850, etc. Our analysis of the optical and near-infrared images (both ground-based and those from the Hubble Space Telescope) revealed circumnuclear minispirals in five objects. The presence of an inner (secondary) bar in the galaxy images is shown to have no effect on the circumnuclear kinematics of the gas and stars. Thus, contrary to popular belief, the secondary bar is not a dynamically decoupled galactic structure. We conclude that the so-called double-barred galaxies are not a separate type of galaxies but are a combination of objects with distinctly different morphology of their circumnuclear regions.

astro-ph↗

arXiv2002

A Spectroscopic Study of the Peculiar Galaxy UGC 5600

We present our observations of the galaxy UGS 5600 with a long-slit spectrograph (UAGS) and a multi-pupil field spectrograph (MPFS) using the 6-m telescope at Special Astrophysical Observatory. Radial-velocity fields of the stellar and gaseous components were constructed for the central region and inner ring of the galaxy. We proved the existence of two almost orthogonal kinematic subsystems and conclude that UGC 5600 is a galaxy with an inner polar ring. In the circumnuclear region, we detected noncircular stellar motions and suspected the existence of a minibar. The emission lines are shown to originate in H II regions. We estimated the metallicity from the intensity ratio of the [NII]$\lambda6583$ and \Ha lines to be nearly solar, which rules out the possibility that the polar ring was produced by the accretion of gas from a dwarf companion.

astro-ph↗

arXiv2002

2D spectroscopy of double-barred galaxies

The first results of the observational program of the study of 2D-kinematics in double-barred galaxies are presented. We show that, for the main part of the sample, the inner bars do not affect the circumnuclear stellar kinematics. Therefore, they are not dynamically decoupled structures. Various types of non-circular gas motion were found in many galaxies. The analysis of the ground-based and HST optical and NIR images reveals mini-spirals in about half of the investigated objects. We suggest that so called ``double-barred galaxies'' are, in fact, galaxies with very different circumnuclear structure.

astro-ph↗

arXiv2002

Fabry-Perot observations at the 6m telescope

A current status of the observations with Interferometer Fabry-Perot (IFP) at the 6m telescope are described. A reduction of the data obtaining with a new focal reducer SCORPIO in IFP mode are outlined.

astro-ph↗

arXiv2001

Observations of Stellar Objects at a Shell Boundary in the Star-Forming Complex in the Galaxy IC1613

The single region of ongoing star formation in the galaxy IC 1613 has been observed in order to reveal the nature of compact emission-line objects at the edges of two shells in the complex, identified earlier in H-alpha line images. The continuum images show these compact objects to be stars. Detailed spectroscopic observations of these stars and the surrounding nebulae were carried out with an integral field spectrograph MPFS mounted on the 6m telescope of the Special Astrophysical Observatory. The resulting stellar spectra were used to determine the spectral types and luminosity classes of the objects. An Of star we identified is the only object of this spectral type in IC 1613. The results of optical observations of the multi-shell complex are compared to 21cm radio observations. The shells harboring the stars at their boundaries constitute the most active part of the star-forming region. There is evidence that shocks have played an important role in the formation of the shells.

astro-ph↗

arXiv2001

Helical structures in Seyfert galaxies

The Seyfert galaxies with Z-shaped emission filaments in the Narrow Line Region (NLR) are considered. We assume that observable Z-shaped structures and velocity pattern of NLR may be explained as tridimensional helical waves in the ionization cone.

astro-ph↗

arXiv2001

Measurement of radial velocities and velocity dispersion of stars in circumnuclear regions of galaxies using the 2D spectrosopy technique

A procedure is described of construction of velocity fields and velocity dispersion of the stellar component in the central regions of galaxies on the basis of data obtained with the integral field spectrograph MPFS. Cross-correlation and Fourier quotients techniques adapted for 2D spectra reduction are used. A detailed discussion is given of the problems of providing for the instrumental profile in measuring the velocity dispersion. Using the existing version of the spectrograph, one can measure radial velocities and the dispersion of velocities to an accuracy of 5-10 km/s and 10-15 km/s, respectively. As an example the double-barred galaxy NGC2950 is considered.

astro-ph↗

arXiv2001

Velocity dispersion of stars and gas motion in double-barred galaxies

The current state of the problem of double-barred galaxies investigation is reviewed. The necessity for application of the panoramic spectroscopy methods to a detailed study of kinematics of these objects is being proved. The first results of observing double-barred galaxies at the 6m telescope using the multipupil spectrograph MPFS and the scanning interferometer Fabry-Perot are described.

astro-ph↗

arXiv2001

Host Galaxies of Gamma-ray Bursts: Spectral Energy Distributions and Internal Extinction

We present BVRcIc broad-band flux spectra for the host galaxies of GRB970508, GRB980613, GRB980703, GRB990123 and GRB991208 obtained with the 6-m telescope of SAO RAS. The BVRcIc of these hosts are best fitted by the spectral properties of template SEDs of starburst galaxies and that there is a significant internal extinction in these host galaxies. We derived the absolute magnitudes of the GRB host galaxies making use of SEDs for the starburst galaxies. We performed the population synthesis modeling of the continuum spectral energy distribution of the host galaxies of GRB970508 and GRB980703 using different extinction laws and assuming burst and exponential scenarios of star formation. The comparison of BVRcIc broad-band flux spectra with the local starburst galaxies templates and theoretical templates as well as direct estimates (using Balmer emission lines) of the internal extinction shows that it is likely to be of great importance to take into account effects of the internal extinction in the host galaxies. From the SED of the host galaxy of GRB991208 and from the intensity of their spectral lines it follows that this is a GRB galaxy with the highest massive star-formation rate of all known GRB galaxies. The reduced luminosity of these dusty galaxies (e.g. for the host of GRB970508 A_V\sim 2 mag, for the host of GRB980703 A_V\sim 0.6 mag and for the host of GRB991208 A_V\sim 2 mag) could explain the observational fact: none of the observed GRB host galaxies with known distances is brighter than the local galaxies with the luminosity L_*.

astro-ph↗

arXiv2001

Interstellar Medium Surrounding the WO Star in the Galaxy IC 1613: New Optical and Radio Observations

Observations of the nebula S3 associated with the WO star in the galaxy IC 1613 and of an extended region surrounding S3 are reported. The star and bright core of the nebula were observed with a multipupil fiber spectrograph mounted on the 6-m telescope of the Special Astrophysical Observatory of the Russian Academy of Sciences. Images in the principle spectral lines and integrated spectra of the star and three compact clumps were obtained, and the radial-velocity field constructed. An extended region of the galaxy was observed with the Very Large Array at 21 cm. A giant ring or HI shell enclosing a large fraction of the stellar population in IC 1613 was discovered. The WO star and associated bipolar nebula, which we discovered earlier, lies at the inner edge of the H ring. A local HI deficiency and two arc-like HI ridges were also detected for the first time, and probably represent the neutral component of the bipolar shell surrounding the WO star. The two arc-like ridges may also have been produced by the collective stellar wind (and supernova explosions?) in OB association No. 9 from the list of Hodge. A scenario for the formation of the extended bipolar feature is discussed, based on the new data.

astro-ph↗

arXiv2001

The extraordinarily bright optical afterglow of GRB 991208 and its host galaxy

Observations of the extraordinarily bright optical afterglow (OA) of GRB 991208 started 2.1 d after the event. The flux decay constant of the OA in the R-band is -2.30 +/- 0.07 up to 5 d, which is very likely due to the jet effect, and after that it is followed by a much steeper decay with constant -3.2 +/- 0.2, the fastest one ever seen in a GRB OA. A negative detection in several all-sky films taken simultaneously to the event implies either a previous additional break prior to 2 d after the occurrence of the GRB (as expected from the jet effect). The existence of a second break might indicate a steepening in the electron spectrum or the superposition of two events. Once the afterglow emission vanished, contribution of a bright underlying SN is found, but the light curve is not sufficiently well sampled to rule out a dust echo explanation. Our determination of z = 0.706 indicates that GRB 991208 is at 3.7 Gpc, implying an isotropic energy release of 1.15 x 10E53 erg which may be relaxed by beaming by a factor > 100. Precise astrometry indicates that the GRB coincides within 0.2" with the host galaxy, thus given support to a massive star origin. The absolute magnitude is M_B = -18.2, well below the knee of the galaxy luminosity function and we derive a star-forming rate of 11.5 +/- 7.1 Mo/yr. The quasi-simultaneous broad-band photometric spectral energy distribution of the afterglow is determined 3.5 day after the burst (Dec 12.0) implying a cooling frequency below the optical band, i.e. supporting a jet model with p = -2.30 as the index of the power-law electron distribution.

astro-ph↗

arXiv2000

Gas motions in the plane of the spiral galaxy NGC 3631

The velocity field of the nearly face-on galaxy NGC 3631, derived from observations in the H alpha line and the HI radio line, is analysed to study perturbations related to the spiral structure of the galaxy. We confirm our previous conclusion that the line-of-sight velocity field gives evidence of the wave nature of the observed two-armed spiral structure. Fourier analysis of the observed velocity field is used to determine the location of corotation of the spiral structure of this galaxy, and the radius of corotation R_c is found to be about 42 arcsec, or 3.2 kpc. The vector velocity field of the gas in the plane of the disc is restored, and taking into account that we previously investigated vertical motions, we now have a full 3D gaseous velocity field of the galaxy. We show clear evidence of the existence of two anticyclonic and four cyclonic vortices near corotation in a frame of reference rotating with the spiral pattern. The centres of the anticyclones lie between the observed spiral arms. The cyclones lie close to the observed spirals, but their centres are shifted from the maxima in brightness.

astro-ph↗

arXiv2000

A Giant Bipolar Shell around the WO star in the Galaxy IC 1613: Structure and Kinematics

Observations of the nebula associated with the WO star in the galaxy IC 1613 are presented. The observations were carried out with a scanning Interferometer Fabry-Perot in H_alpha at the 6m Special Astrophysical Observatory telescope; narrow-band H_alpha and [OIII] images were obtained with the 4-m KPNO telescope. The monochromatic H_alpha image clearly reveals a giant bipolar shell structure outside the bright nebula S3. The sizes of the southeastern and northwestern shells are 112x77 pc and (186-192)x(214-224) pc, respectively. We have studied the object's kinematics for the first time and found evidence for expansion of both shells. The expansion velocities of the southeastern and northwestern shells exceed 50 and 70 km/s, respectively. We revealed a filamentary structure of the shells and several compact features in the S3 core. A scenario is proposed for the formation of the giant bipolar structure by the stellar wind from the central WO star located at the boundary of a dense ``supercavity'' in the galaxy's H I distribution.

astro-ph↗