73 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
Spectrophotometric investigations of Blue Compact Dwarf Galaxies: Markarian 35
We present results from a detailed spectrophotometric analysis of the blue
compact dwarf galaxy Mrk 35 (Haro 3), based on deep optical (B,V,R,I) and
near-IR (J,H,K) imaging, Halpha narrow-band observations and long-slit
spectroscopy. The optical emission of the galaxy is dominated by a central
young starburst, with a bar-like shape, while an underlying component of stars,
with elliptical isophotes and red colors, extends more than 4 kpc from the
galaxy center. High resolution Halpha and color maps allow us to identify the
star-forming regions, to spatially discriminate them from the older stars, and
to recognize several dust patches. We derive colors and Halpha parameters for
all the identified star-forming knots. Observables derived for each knot are
corrected for the contribution of the underlying older stellar population, the
contribution by emission lines, and from interstellar extinction, and compared
with evolutionary synthesis models. We find that the contributions of these
three factors are by no means negligible and that they significantly vary
across the galaxy. Therefore, careful quantification and subtraction of
emission lines, galaxy host contribution, and interstellar reddening at every
galaxy position, are essential to derive the properties of the young stars in
BCDs. We find that we can reproduce the colors of all the knots with an
instantaneous burst of star formation and the Salpeter initial mass function
with an upper mass limit of 100 M_solar. In all cases the knots are just a few
Myr old. The underlying population of stars has colors consistent with being
several Gyr old.Comment: 21 pages, 13 figures. Accepted for publication in ApJ, tentatively
scheduled for the ApJ November 1, 2007 v669n1 issu
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