Publications (19)4.41 Total impact
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Article: WSRT observations and surface photometry of two unusual spiral galaxies
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ABSTRACT: We discuss the results of a mass decomposition of two spiral galaxies, NGC 6824 and UGC 11919. In a previous analysis of the Hyperleda catalog, the galaxies were identified as having a peculiar dynamical $M/L$. The aim of this study is to confirm or disprove the preliminary findings, indicating a non-standard stellar initial mass function (IMF) for the galaxies. The surface photometry in B, V, and R bands was carried out with the Apache Point 0.5-m telescope and the \ion{H}{I} data cubes were obtained with the Westerbork Synthesis Radio Telescope (WSRT). Photometric profiles were decomposed into bulge and exponential disk components. Using the obtained \ion{H}{I} data cubes, rotation curves of both galaxies were constructed. Employing the photometric profiles, the mass distribution of the galaxies was decomposed into mass components: bulge, stellar disk, gas, and pseudo-isothermal dark halo. We conclude that NGC 6824 possesses a stellar disk with mass-to-light ratio $(M/L_B)_{\rm disk} = 2.5$, in agreement with its color $(B-V)_0$. On the contrary, UGC 11919 appears to have a very lightweight disk. Its dynamically estimated mass corresponds to a low stellar disk mass-to-light ratio $(M/L_B)_{\rm disk} \approx 0.5$. Under standard assumptions, this ratio does not agree with the relatively red color of the disk, while a bottom light stellar initial mass function is needed to explain the observations.05/2013; -
Article: Interaction between collisionless galactic discs and non-axisymmetric dark matter haloes
mnras. 03/2013; -
Article: Interaction between collisionless galactic discs and nonaxissymmetric dark matter haloes
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ABSTRACT: Using $N$-body simulations ($N\sim 10^6 - 10^7$), we examine how a non-axisymmetric dark halo affects the dynamical evolution of the structure in collisionless (stellar) discs. We demonstrate how the model parameters such as mass of the halo, initial conditions in the disc and the halo axes ratio affect morphology and kinematics of the stellar discs. We show that a non-axisymmetric halo can generate a large-scale spiral density pattern in the embedded stellar disc. The pattern is observed in the disc for many periods of its revolution, even if the disc is gravitationally over-stable. The growth of the spiral arms is not accompanied by significant dynamical heating of the disc, irrelevant to its initial parameters. We also investigate transformation of the dark halo's shape driven by the long-lived spiral pattern in the disc . We show that the analysis of the velocity field in the stellar disc and in the spiral pattern gives us a possibility to figure out the spatial orientation of the triaxial-shaped dark halo and to measure the triaxiality.Monthly Notices of the Royal Astronomical Society. 02/2013; 431(2):1230-1239. -
Article: Do Disk Galaxies with Abnormally Low Mass-to-Light Ratios Exist?
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ABSTRACT: We performed the photometric B, V and R observations of nine disk galaxies that were suspected in having abnormally low total mass-to-light (M/L) ratios for their observed color indices. We use our surface photometry data to analyze the possible reasons for the anomalous M/L. We infer that in most cases this is a result of errors in photometry or rotational velocity, however for some galaxies we cannot exclude the real peculiarities of the galactic stellar population. The comparison of the photometric and dynamical mass estimates in the disk shows that the low M/L values for a given color of disks are probably real for a few our galaxies: NGC 4826 (Sab), NGC 5347 (Sab), and NGC 6814 (Sb). The small number of such galaxies suggests that the stellar initial mass function is indeed universal, and that only a small fraction of galaxies may have a non-typical low-mass star depleted initial mass function. Such galaxies require more careful studies for understanding their star formation history.12/2011; -
Article: Gas Emission Spectrum in the Irr Galaxy IC 10
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ABSTRACT: Spectroscopic long-slit observations of the dwarf Irr galaxy IC 10 were conducted at the 6-m Special Astrophysical Observatory telescope with the SCORPIO focal reducer. The ionized-gas emission spectra in the regions of intense current star formation were obtained for a large number of regions in IC 10. The relative abundances of oxygen, N+, and S+ in about twenty HII regions and in the synchrotron superbubble were estimated. We found that the galaxy-averaged oxygen abundance is 12 + log(O/H) = 8.17 +- 0.35 and the metallicity is Z = 0.18 +- 0.14 Z_sun. Our abundances estimated from the strong emission lines are found to be more reliable than those obtained by comparing diagnostic diagrams with photoionization models. Comment: Abridged; accepted in Astronomy Letters10/2009; -
Article: 3D spectroscopic study of galactic rings: formation and kinematics
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ABSTRACT: In this review we consider various ring structures that are observed in galaxies. Formation and evolution of the rings are interesting problems in studies of galactic morphology. They are related to such fundamental aspects of galactic evolution and dynamics as the nature and distribution of the dark matter in galaxies, galactic interactions and internal secular evolution of galactic substructures. A significant fraction of galactic rings forms in the disks due to gravitational torques from bar-like patterns. In contrast to this internally driven origin, the phenomenon of the polar-ring galaxies is closely connected with the processes of intergalactic interactions and merging. A rare class of collisional rings reveals the density waves triggered in the stellar and gaseous disks after a strong head-on collision with a companion. We briefly review the status of studies of gas kinematics in the rings of different origin. We stress that velocity fields of the ionized gas obtained with the Fabry-Perot interferometers provide a very important information for these studies. Comment: 13 pages, 4 figures, New Astronomy Reviews (proceeding of 7th SCSLSA), in press08/2009; -
Article: Propagating Star Formation in the Collisional Ring Galaxy Arp 10
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ABSTRACT: Propagating star formation in a collisional ring galaxy Arp10 is investigated by a complex approach, which includes the broad- and narrow-band photometry, long- slit spectroscopy, and scanning Fabry-Perot spectroscopy. The ionized gas velocity field obtained with best spatial resolution to date indicates a non- isotropic expansion of the outer ring with a maximum velocity 110km/s. Strong vertical and non-circular motions are also seen in the vicinity of the inner ring. Our kinematic data suggest that Arp10 has a small inclination i=22\degr and high total (luminous plus dark matter) mass of about $10^{12} M_{\odot}$ within a 50 kpc radius.The abundance of oxygen 12 + log(O/H) in both star- forming rings is about 8.6.The analysis of spectral indices provides an estimate on the propagation velocities of both rings and metallicity of the pre-collision stellar population.A small "knot" near the nucleus of Arp10,which was previously suspected as a possible candidate for collision, is now unambiguously identified as the "intruder" of at least 1/4 of the total mass of Arp~10.We use a simplified two-dimensional hydrodynamic modeling of galaxy collisions to test a collisional origin of Arp10. We confirm that the sizes of the inner and outer rings, maximum expansion velocity of the outer ring, and radial profile of the gas circular velocity can be reproduced by a near-central collision with the intruder galaxy, which occurred approximately 85Myr ago. We acknowledge that an apparent crescent- shaped distribution of H$\alpha$ emission in the outer ring is caused by a star formation threshold in the gas disk of Arp10.03/2007; -
Article: Long-slit and Fabry-Perot spectroscopy of collisional ring galaxy Arp 10
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ABSTRACT: We present results of Fabry-Perot and long-slit spectroscopy of the peculiar galaxy Arp 10. The ionized gas velocity field shows evidence for significant radial motions in both outer and inner galactic rings. Long-slit spectroscopy reveals gradients of age and metallicity of stellar population in agreement with the propagating nature of star formation in the galaxy. We present strong evidence that a small ``knot'' at 5 arcsec from the center of Arp 10 is its dwarf elliptic satellite, the most probable ``intruder'' responsible for triggering the expanding rings in Arp 10.02/2005; -
Article: Bending instability in galaxies: the stellar disk thickness and the mass of spheroidal component
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ABSTRACT: We present results of numerical N-body simulations of a galactic stellar disk embedded into a spherical dark halo. The non-linear dynamics of bending instabilities developing in the disk is studied. The bending modes, axisymmetric and not, are considered as main factors increasing the disk thickness. The relation between the disk vertical scale height and the halo+bulge-to-disk mass ratio is inferred. The method of estimation of the spherical-to-disk mass ratio for edge-on spiral galaxies based on this relation is studied and applied to constrain the spherical subsystem mass and the mass of dark halos (M_h/M_d) in seven edge-on galaxies. The values of M_h/M_d are of order 1 for our galaxies.06/2004; -
Article: A Thickness of Stellar Disks of Edge-on Galaxies and Position of Their Truncation Radii
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ABSTRACT: The relationship between the geometrical properties of stellar disks (a flatness and truncation radius) and the disk kinematics are considered for edge-on galaxies. It is shown that the observed thickness of the disks and the approximate constancy of their thickness along the radius well agrees with the condition of their marginal local gravitational stability. As a consequence, those galaxies whose disks are thinner should harbor more massive dark haloes. The correlation between the de-projeced central brightness of the disks and their flatness is found (the low surface brightness disks tend to be the thinniest ones). We also show that positions of observed photometrically determined truncation radii $R_{cut}$ for the stellar disks support the idea of marginal local gravitational stability of gaseous protodisks at $R =R_{cut}$, and hence the steepening of photometric profiles may be a result of too inefficient star formation beyond $R_{cut}$.01/2003; -
Article: BVRI surface photometry of the galaxy NGC 3726
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ABSTRACT: We present BVRI surface photometry of the late-type spiral galaxy NGC 3627. The distributions of the color indices and extinction-independent Q indices show that the observed photometric asymmetry in the inner part of the galaxy, including the bar, is due to an asymmetric distribution of absorbing material. The bluest regions of star formation are located in a ring surrounding the bar. The background-subtracted color indices of individual blue knots are used to estimate the ages of young stellar aggregates. In combination with previously published photometric data, our measurements indicate that the R-band profile of the disk is rather flat in its inner part (r<50″) and becomes steeper further from its center. We estimate the mass of the disk and dark halo by decomposing the rotation curve. The mass-to-light ratio M/L B for the stellar disk is ≈1.4. The galaxy possesses a massive dark halo; however, the mass of the disk exceeds that of the halo in the inner part of the galaxy, which displays a regular spiral structure.Astronomy Reports 08/2002; 46(9):704-711. · 0.73 Impact Factor -
Article: Disk boundaries in spiral galaxies
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ABSTRACT: We explore the hypothesis that the outer boundaries (“cutoffs”) of the stellar disks observed in many galaxies are determined by the condition of local gravitational (Jeans) stability for the gaseous protodisks at large galactocentric distances. The ratio of the surface density of the disk Σdisk to the critical value for Jeans instability Σcrit is computed for a number of galaxies, assuming that the gas velocity dispersion in the forming disk corresponded to its current thickness and that the disk itself is in a quasi-equilibrium state. The mean estimated stellar velocity dispersion in the vicinity of the cutoff (12 km/s) is close to the typical velocity dispersions of gaseous clouds in disk galaxies. At greater distances, such velocity dispersions should ensure gravitational stability of the disk both at the present epoch and in the past. The cutoff radius of the disk R cut is correlated with other disk parameters, and the ratio Σdisk/Σcrit at R cut is close to unity in most cases. We conclude that the available observational data agree well with the hypothesis that stellar disk cutoffs are due to a rapid decrease in the star-formation rate beyond R cut, where the gaseous disk has always been stable.Astronomy Reports 08/2002; 46(9):721-730. · 0.73 Impact Factor -
Article: Relationship between the thickness of stellar disks and the relative mass of a dark galactic halo
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ABSTRACT: We analyze the R-and K s-band photometric profiles for two independent samples of edge-on galaxies. The thickness of old stellar disks is shown to be related to the relative masses of the spherical and disk components of galaxies. The radial-to-vertical scale length ratio for galactic disks increases (the disks become thinner) with increasing total mass-to-light ratio of the galaxies, which reflects the relative contribution of the dark halo to the total mass, and with decreasing central deprojected disk brightness (density). Our results are in good agreement with numerical models of collisionless disks that evolved to a marginally stable equilibrium state. This suggests that, in most galaxies, the vertical stellar-velocity dispersion, on which the equilibrium-disk thickness depends, is close to a minimum value that ensures disk stability. The thinnest edge-on disks appear to be low-brightness galaxies in which the dark-halo mass far exceeds the stellar-disk mass.Astronomy Letters 07/2002; 28(8):527-535. · 0.99 Impact Factor -
Article: Combined color indices and photometric structures of the galaxies NGC 834 and NGC 1134
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ABSTRACT: Surface BVRI photometry is presented for two spiral galaxies with a complex photometric structure: NGC 834 and NGC 1134. We propose to introduce the combined color indices Q BVI and Q VRI to investigate the photometric structure of the galaxies. These color indices depend only slightly on selective absorption, which allows them to be used to study the photometric structure of “dusty” galaxies. Evolutionary stellar-population models show that Q BVI is most sensitive to the presence of blue stars, while Q VRI depends on local Hα equivalent width. A ring with active star formation manifests itself on the Q BVI map for NGC 834 at a distance of ∼15 from its center, and a spiral structure shows up on the Q VRI map for NGC 1134 in its inner region. The Q BVI –Q VRI diagram can provide information about the current stage of a star's formation in various galactic regions. A comparison of the color indices for the galaxies with their model values allows us to estimate the color excesses and extinction in various galactic regions.Astronomy Letters 03/2001; 27(4):217-227. · 0.99 Impact Factor -
Article: Comparison of Star Formation Rate estimations from $H_{\alpha}$, FIR and radio data
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ABSTRACT: We used three indicators of massive star formation: $H_{\alpha}$, FIR and non-thermal radio luminosities, to compare estimations of Star Formation Rate (SFR) for the sample of 34 spiral galaxies. To adjust SFR values, obtained from different indicators, we considered the slope $\alpha$ and/or upper mass limit $M_{up}$ of Initial Mass Function (IMF) as free parameters. The best agreement between these indicators reaches for $M_{up} \approx 60 - 100 ~M_{\odot}$ and $\alpha \approx -3.1 $ in the high mass end of IMF ($M > 10 ~M_{\odot}$). Parallel with SFR we also estimated FIR excess $X_{FIR}$ defined as a fraction of the observed FIR which is not related to young massive stars directly. $X_{FIR}$ is found to be well correlated with types of spiral galaxies and their colors (B-V): the redder a galaxy the higher is its FIR excess. We conclude that for any parameters of IMF the observed FIR flux of early type spiral galaxies needs the additional source of energy but the massive star radiation. Comment: 7 pages including 3 PostScript figures. To be published in "The Evolution of galaxies on Cosmological timescales", Ap. & Space Science, Proceedings of the meeting held at Puerto de la Cruz (Spain) on November 30-December 5, 199801/2000; -
Article: An estimate for the Hubble constant using a criterion for gravitational stability of gaseous disks
Astronomy Letters 12/1995; 22:71-78. · 0.99 Impact Factor -
Article: Star-Formation Efficiency and Gravitational Stability of Gaseous Disks in Galaxies
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Article: 3D spectroscopic study of galactic rings: Formation and kinematics
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ABSTRACT: Various ring structures observed in galaxies are considered. Formation and evolution of the rings are interesting problems in studies of the galactic morphology that is related to fundamental aspects of galactic evolution and dynamics: the nature and distribution of the dark matter, galactic interactions and internal secular evolution of the galaxies. A significant fraction of galactic rings forms in the disks due to gravitational torques from bar-like patterns. In contrast to this internally driven origin, the phenomenon of the polar-ring galaxies is closely connected with the processes of intergalactic interactions and merging. A more rare class of collisional rings reveals the density waves triggered in the stellar and gaseous disks after a strong head-on collision with a companion. We briefly review the status of studies of gas kinematics in the rings of different origin. We stress that velocity fields of the ionized gas obtained with the Fabry–Pérot interferometers provide a very important information for these studies.New Astronomy Reviews. -
Article: The Thickness of Stellar Disks of Edge-on Galaxies and Their Truncation Radii
[show abstract] [hide abstract]
ABSTRACT: The relationship between geometrical properties of stellar disks (the flatness and the truncation radius) and disk kinematics are considered for edge-on galaxies. It is shown that the observed thickness of the disks agrees with the condition of marginal local gravitational stability. As a consequence, those galaxies whose disks are thinner should harbor more massive dark halos. A correlation between the de-projected central brightness of disks and their flatness is found (low surface brightness disks tend to be the thinnest ones). We also show that the positions of the observed photometrically determined truncation radii $R_{\rm cut}$ of stellar disks agree well with the hypothesis of marginal local gravitational stability of gaseous proto-disks at $R =R_{\rm cut}$.â©http://dx.doi.org/10.1051/eas:2003157.
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- Astronomy Letters (3)
- Astronomy Reports (2)
Institutions
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2013
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Lomonosov Moscow State University
Moscow, Moscow, Russia
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