1,461 research outputs found
Polar rings dynamics in the triaxial dark matter halo
Spectroscopic observations at the Russian 6-m telescope are used to study the
two polar ring galaxies (PRGs) from the catalogue by Moiseev et al.: SPRC-7 and
SPRC-260. We have analyzed the kinematics of the stellar component of the
central galaxies as well as the ionized gas kinematics in the external ring
structures. The disc-halo decomposition of rotation curves in two perpendicular
directions are considered. The observed 2D velocity fields are compared with
the model predictions for different dark halo shapes. Based on these data, we
constrain that for potential of DM halo semiaxis ratios is , for
SPRC-7 and , for SPRC-260. Using 3D hydrodynamic simulations we
also study the dynamics and evolution of the polar component in the potential
of the galactic disc and dark halo for these two galaxies. We show that the
polar component is dynamically quasi-stable on the scale of dynamical
times (about a few Gyr). This is demonstrate the possibility for the growth of
a spiral structure, which then steadily transforms to a lopsided gaseous system
in the polar pane.Comment: 4 pages, 4 figures, to pe published in EWASS-SPS4, Roma, P. Di Matteo
and C. Jog, ed
Dynamic dislocation drag near to a point of martensitic transformation
The influence of coherent interface on dissipations of mechanical energy of
driven dislocations near to a point of martensite type phase transition is
considered. The expressions for dynamic braking of dislocations, owing to
losses of energy on excitation of deformations-type phase transition are
received.Comment: 6 pages, 1 figure
Search for gas accretion imprints in voids: I. Sample selection and results for NGC 428
We present the first results of a project aimed at searching for gas
accretion events and interactions between late-type galaxies in the void
environment. The project is based on long-slit spectroscopic and scanning
Fabry-Perot interferometer observations performed with the SCORPIO and
SCORPIO-2 multimode instruments at the Russian 6-m telescope, as well as
archival multiwavelength photometric data. In the first paper of the series we
describe the project and present a sample of 18 void galaxies with oxygen
abundances that fall below the reference `metallicity-luminosity' relation, or
with possible signs of recent external accretion in their optical morphology.
To demonstrate our approach, we considered the brightest sample galaxy NGC 428,
a late-type barred spiral with several morphological peculiarities. We analysed
the radial metallicity distribution, the ionized gas line-of-sight velocity and
velocity dispersion maps together with WISE and SDSS images. Despite its very
perturbed morphology, the velocity field of ionized gas in NGC 428 is well
described by pure circular rotation in a thin flat disc with streaming motions
in the central bar. We also found some local non-circular gas motions clearly
related to stellar feedback processes. At the same time, we revealed a
circumnuclear inclined disc in NGC 428 and a region with significant residual
velocities that could be considered as a result of a recent (<0.5 Gyr)
accretion event. The observed oxygen abundance gradient does not contradict
this conclusion.Comment: Accepted for publication in MNRAS; 13 pages, 10 figures, 4 table
SDSS J170745+302056: a low surface brightness galaxy in a group
On the basis of the SDSS survey and spectral observations with the 6-m
telescope of SAO RAS, we have peformed a detailed study of SDSS J170745+302056.
By combination of its characteristics -- exponential surface brightness
distribution, central surface brightness of stellar disk \mu_0(B) =
23.25\,^m/\square", blue colors, low metallicity and low star formation rate
-- the galaxy is a typical low surface brightness spiral galaxy. Exponential
scalelength of the galaxy is 3 kpc, its optical diameter exceeds 20
kpc. SDSS J170745+302056 is a member of a group of five galaxies and probably
it is in interaction with UGC 10716. The existence of a large low surface
brightness galaxy in such a dense environment is very unusual.Comment: 8 pages, 4 figure
The shape of dark matter halo in PRG NGC 4262
With the aim to determine the spatial distribution of dark matter, we
investigate the polar ring galaxy NGC 4262. We used the stellar kinematics data
for the central galaxy obtained from optical spectroscopy together with
information about the kinematics of the neutral hydrogen for polar component.
It was shown that NGC 4262 is the classic polar ring galaxy case with the
relative angle of between components. From simulations of the
central galaxy and ring kinematics we found that the shape of the dark matter
distribution varies strongly with the radius. Namely, the dark matter halo is
flattened towards the galactic disk plane , however it is prolate to
the orthogonal (polar) plane far beyond the central galaxy . Also, the
simulations of the ring evolution let us to confirm the stability of the ring
and the formation of quasi-spiral structures within it.Comment: 4 pages, 2 figures, proceedings of "Multi-spin galaxies", Napoli,
October 201
To be or not to be oblate: the shape of the dark matter halo in the polar ring galaxies
With the aim to determine the spatial distribution of the dark matter halo,
we investigate two polar ring galaxies NGC 4262 and SPRC-7. For both galaxies
the stellar kinematics data for the central galaxy were obtained from optical
spectroscopy at the 6-m telescope of the Special Astrophysical Observatory of
the Russian Academy of Sciences. The information about polar gaseous components
was taken from the optical 3D-spectroscopic observations of ionized gas (for
SPRC-7) and H {\sc i} radio observations (for NGC 4262). SPRC-7 is the system
with a relative angle towards the central galaxy and a
quite massive stellar-gaseous polar component. Meanwhile NGC 4262 is the
classic polar case with where the polar ring mainly
consists of neutral gas with a negligible stellar contribution to the mass. We
are hence dealing with two different systems and the results are quite diverse
too. The observed properties of both galaxies were compared with the results of
self consistent simulations of velocity fields of the polar component along
with the rotation curve of the central lenticular galaxy. For SPRC-7 we have
found a slightly flattened halo towards the polar plane with the axis ratio
for the isothermal halo model and for the NFW model. The case of NGC 4262 is more unusual, the shape of the
dark matter distribution varies strongly with radius. Namely, the dark matter
halo is fattened in the vicinity of the galactic disc (), however it is prolate far beyond the central galaxy (
for the isothermal halo and for NFW).Comment: 15 pages, 11 figures, Accepted for publication in MNRA
A close look at the well-known Seyfert galaxy: extended emission filaments in Mrk6
Using various techniques of optical observations at the 6-m Russian telescope
(emission-line images, long-slit and 3D spectroscopy), we have studied
large-scale morphology and kinematics of the ionized gas in the Seyfert galaxy
Mrk6. Having a significantly deeper images and spectra than those in previous
works, we have not only mapped the ionized gas in the stellar disc but also
found a system of faint filaments elongated in the NE direction up to a
projected distance of 40 kpc (4.3R). Kinematics as well as an ionization
state of the filament gas suggest the scenario that hard radiation of the
active nucleus illuminated the matter accreted from outside and orbiting almost
orthogonally to the Mrk 6 stellar disc. A possible source of gas accretion is
still unknown, a deep image taken with the 1-m Byrakan Schmidt telescope does
not show any stellar counterparts at the level of 27-28 mag/arcsec.Comment: 6 pages, 5 figures. Accepted for publication in MNRA
Application of the global modal approach to spiral galaxies
We have tested the applicability of the global modal approach in the density
wave theory of spiral structure for a sample of six spiral galaxies: NGC 488,
NGC 628, NGC 1566, NGC 2985, NGC 3938 and NGC 6503. The galaxies demonstrate a
variety of spiral patterns from the regular open and tightly wound spiral
patterns to a multi-armed spiral structure. Using the observed radial
distributions of the stellar velocity dispersions and the rotation curves we
have constructed equilibrium models for the galactic disks in each galaxy and
analyzed the dynamics of the spiral perturbations using linear global modal
analysis and nonlinear hydrodynamical simulations. The theory reproduces
qualitatively the observed properties of the spiral arms in the galactic disks.
Namely the theory predicts observed grand-design spiral structure in the galaxy
NGC 1566, the tightly-wound spirals in galaxies NGC 488 and NGC 2985, the
two-armed spiral pattern with the third spiral arm in the galaxy NGC 628, and
the multi-armed spiral structure in the galaxies NGC 3938 and NGC 6503. In
general, more massive disks are dominated by two-armed spiral modes. Disks with
lower mass, and with lower velocity dispersion are simultaneously unstable for
spiral modes with different numbers of arms, which results in a more
complicated pattern.Comment: 21 pages, 19 EPS and 1 JPEG figure
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.Comment: 4 pages, 1 figure, to appear in the proceedings of "The Evoution of
Galaxies. III. From simple approaches to self-consistent models" (Kiel, July
2002), G. Hensler et al. (eds.
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{\deg}; (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.Comment: 15 pages, 8 figures, accepted for publication in MNRA
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