9 research outputs found
NGC 7468: a galaxy with an inner polar disk
We present our spectroscopic observations of the galaxy NGC 7468 performed at
the 6-m Special Astrophysical Observatory telescope using the UAGS long-slit
spectrograph, the multipupil fiber spectrograph MPFS, and the scanning
Fabry-Perot interferometer (IFP). We found no significant deviations from the
circular rotation of the galactic disk in the velocity field in the regions of
brightness excess along the major axis of the galaxy (the putative polar ring).
Thus, these features are either tidal structures or weakly developed spiral
arms. However, we detected a gaseous disk at the center of the galaxy whose
rotation plane is almost perpendicular to the plane of the galactic disk. The
central collision of NGC 7468 with a gas-rich dwarf galaxy and their subsequent
merging seem to be responsible for the formation of this disk.Comment: 8 pages, 6 figures, accepted in Astronomy Letters, 2004, vol 30., N
9, p. 58
The Gas Content in Galactic Disks: Correlation with Kinematics
We consider the relationship between the total HI mass in late-type galaxies
and the kinematic properties of their disks. The mass for galaxies with
a wide variety of properties, from dwarf dIrr galaxies with active star
formation to giant low-brightness galaxies, is shown to correlate with the
product ( is the rotational velocity, and is the radial
photometric disks scale length), which characterizes the specific angular
momentum of the disk. This relationship, along with the anticorrelation between
the relative mass of HI in a galaxy and , can be explained in terms of the
previously made assumption that the gas density in the disks of most galaxies
is maintained at a level close to the threshold (marginal) stability of a
gaseous layer to local gravitational perturbations. In this case, the
regulation mechanism of the star formation rate associated with the growth of
local gravitational instability in the gaseous layer must play a crucial role
in the evolution of the gas content in the galactic disk.Comment: revised version to appear in Astronomy Letters, 8 pages, 5 EPS
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Deep Near Infrared Mapping of Young and Old Stars in Blue Compact Dwarf Galaxies
We analyze J, H and Ks near-infrared data for 9 Blue Compact Dwarf (BCD)
galaxies, selected from a larger sample that we have already studied in the
optical. We present contour maps, surface brightness and color profiles, as
well as color maps of the sample galaxies. The morphology of the BCDs in the
NIR has been found to be basically the same as in the optical. The inner
regions of these systems are dominated by the starburst component. At low
surface brightness levels the emission is due to the underlying host galaxy;
the latter is characterized by red, radially constant colors and isophotes well
fit by ellipses. We derive accurate optical near--infrared host galaxy colors
for eight of the sample galaxies; these colors are typical of an evolved
stellar population. Interestingly, optical near--infrared color maps reveal the
presence of a complex, large-scale absorption pattern in three of the sample
galaxies. We study the applicability of the Sersic law to describe the surface
brightness profiles of the underlying host galaxy, and find that, because of
the limited surface brightness interval over which the fit can be made, the
derived Sersic parameters are very sensitive to the selected radial interval
and to errors in the sky subtraction. Fitting an exponential model gives
generally more stable results, and can provide a useful tool to quantify the
structural properties of the host galaxy and compare them with those of other
dwarf classes as well as with those of star-forming dwarfs at higher redshifts.Comment: 49 pages, 9 figures, 10 tables, accepted for publication in the
Astrophysical Journa