1,871 research outputs found
Are polar rings indeed polar?
We have considered polar ring galaxy candidates, the images of which can be
found in the SDSS. The sample of 78 galaxies includes the most reliable
candidates from the SPRC and PRC catalogs, some of which already have kinematic
confirmations. We analyze the distributions of studied objects by the angle
between the polar ring and the central disk, and by the optical diameter of the
outer ring structures. In the vast majority of cases, the outer structures lie
in the plane close to polar (within 10-20 deg) which indicates the stability of
the corresponding orbits in the gravitational potential of the halo. Moderately
inclined outer structures are observed only in about 6% of objects which
probably indicates their short lifetime. In such an unstable configuration, the
polar ring would often cross the disk of the galaxy, being smaller than it in
the diameter. We show that the inner polar structures and outer large-scale
polar rings form a single family in the distribution of diameters normalized to
the optical size of the galaxy. At the same time, this distribution is bimodal,
as the number of objects with d_ring= (0.4-0.7)*d_disk is negligible. Such a
shape of size distribution is most likely due to the fact that the stability of
polar orbits in the inner regions of galaxies is maintained by the bulge or the
bar, while in the outer regions it is provided by the spheroidal (or triaxial)
halo.Comment: Corrected version accepted in Astrophysical Bulletin, 8 pages, 5 EPS
figure
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 and the line-of-sight velocity dispersion
profiles and provides an anisotropy-independent estimate of the
galaxy circular speed . The mass-anisotropy degeneracy is effectively
overcome by evaluating at a characteristic radius defined
from {\it local} properties of observed profiles. The sweet radius is expected to lie close to , where , and not
far from the effective radius . 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 -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 -estimate to the X-ray one is equal to with
scatter, i.e. there is no evidence for the large non-thermal pressure
contribution in the gas at . From analysis of the Lick
indices H, 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 in the sample galaxies is for the
Salpeter IMF and for the Kroupa IMF.Comment: accepted for publication in MNRA
Maxwell strata in sub-Riemannian problem on the group of motions of a plane
The left-invariant sub-Riemannian problem on the group of motions of a plane
is considered. Sub-Riemannian geodesics are parametrized by Jacobi's functions.
Discrete symmetries of the problem generated by reflections of pendulum are
described. The corresponding Maxwell points are characterized, on this basis an
upper bound on the cut time is obtained
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.Comment: 8 paged, 7 figures, accepted for publication in A&
- …