12 research outputs found
New insights to the photometric structure of Blue Compact Dwarf Galaxies from deep Near-Infrared studies I. Observations, surface photometry and decomposition of surface brightness profiles
(shortened) We analyze deep Near Infrared (NIR) broad band images for a
sample of Blue Compact Dwarf Galaxies (BCDs), allowing for the quantitative
study of their extended stellar low-surface brightness (LSB) host galaxies. NIR
surface brightness profiles (SBPs) of the LSB hosts agree at large
galactocentric radii with those from optical studies. At small to intermediate
radii, however, the NIR data reveal for more than half of our sample a
significant flattening of the exponential SBP of the LSB host. Such SBPs ("type
V" SBPs, Binggeli & Cameron 1991) have rarely been detected in LSB hosts of
BCDs at optical wavelengths, where the relative flux contribution of the
starburst is stronger than in the NIR and can hide such central intensity
depressions of the LSB host. The structural properties, frequency and physical
origin of type V LSB SBPs in BCDs and other dwarf galaxies have not yet been
systematically studied. Nevertheless, their occurrence in a significant
fraction of BCDs would impose important new constraints to the radial
distribution of their stellar mass, and to the photometric fading of BCDs after
the termination of star-forming activity. Both a modified exponential
(Papaderos et al. 1996a) and the Sersic law give satisfactory empirical
descriptions for type V SBPs. However, we argue that the practical
applicability of Sersic fits to LSB SBPs of BCDs is limited by, e.g., the
extreme sensitivity of the solutions to small SBP uncertainties. Most stellar
LSB host galaxies in the sample show optical-NIR colors indicative of evolved
stellar populations with subsolar metallicity. Unsharp-masked NIR images and
optical-NIR maps reveal numerous morphological details, and cases of
non-uniform dust absorption on spatial scales up to ~1 kpc.Comment: 29 pages, 17 figures; accepted for publication in Astronomy &
Astrophysics; 1 typo in Table 2 corrected; higher resolution images are
available at
http://www.uni-sw.gwdg.de/~knoeske/PUB_LIST/noeske_BCDs_NIR.ps.g
Super Star Clusters in the Blue Dwarf Galaxy UM 462
I present optical observations of the Blue Compact Dwarf Galaxy UM 462. The
images of this galaxy show several bright compact sources. A careful study of
these sources has revealed their nature of young Super Star Clusters. The ages
determined from the analysis of the stellar continuum and are between
few and few tens Myr. The total star formation taking place into the clusters
is about 0.05 . The clusters seem to be located at the
edges of two large round-like structures, possibly shells originated in a
previous episode of star formation. The sizes of the shells compare well with
the ages of the clusters. Evidence for the presence of an evolved underlying
stellar population is found.Comment: 8 pages, 6 figure
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
figure
Near-infrared properties of blue compact dwarf galaxies: the link between solar and low metallicity
We have obtained near-infrared images and spectra of three blue compact dwarf
galaxies of intermediate sub-solar metallicity Tol~35, Tol~3 and UM 462. This
work is part of a larger project aimed to study the star formation and the
stellar populations of low metallicity galaxies in the near-infrared. In this
frame work galaxies of intermediate metallicity represent an important step in
understanding the most extreme cases filling the gap between solar and very low
metallicity galaxies. We have observed HII region like spectra in all three
galaxies; in all cases the star formation episodes are only a few Myr old.
Consistently with a young age our spectra show no evidence for stellar
absorption features typical of supergiants, nor of [FeII] emission typical of
supernovae. The K-band gas fraction ranges from 20 to 40 % showing that gas
emission can significantly contaminate broadband near-infrared colors in young
metal-poor starbursts. We have detected molecular hydrogen in emission in all
three objects. All sources show bright knots superimposed on a lower surface
brighness envelope. The knots are identified with Super Star Clusters; six of
them are present in UM 462. In all galaxies we detect the presence of an old
stellar population.Comment: 10 pages, 10 figure