1,816 research outputs found
Neutral Gas Distributions and Kinematics of Five Blue Compact Dwarf Galaxies
We present the results of high spatial resolution HI observations of five
intrinsically compact dwarf galaxies which are currently experiencing a strong
burst of star formation. The HI maps indicate that these systems have a complex
and clumpy interstellar medium. Unlike typical dwarf irregular galaxies, these
Blue Compact Dwarf (BCD) galaxies exhibit strong central concentrations in
their neutral gas distributions which may provide a clue to the origin of their
strong star-burst activity. Furthermore, while all of the systems do appear to
be rotating, based on observed velocity gradients, the kinematics are complex.
All systems have non-ordered kinematic structure at some level; some of the
extended gas is not necessarily kinematically connected to the main system.
The observed gas distributions and kinematics place constraints on
evolutionary scenarios for BCDs. Evolutionary links between BCDs, dwarf
irregulars, and dwarf ellipticals have been postulated to explain their high
star formation rates and low luminosity, low metallicity nature. The BCDs
appear to have higher central mass concentrations in both gas and stellar
content than the dwarf irregulars, indicating that evolutionary scenarios
connecting these two classes will require mass redistribution. In addition, the
fact that BCDs are rotationally supported systems indicates that BCDs are
unlikely to evolve into dwarf ellipticals without substantial loss of angular
momentum. Thus, while such evolutionary scenarios may still be possible with
the aid of mergers or tidal interactions, the isolated nature of BCDs suggests
that the majority of BCDs will not fade to become objects similar to the
present day dwarf ellipticals.Comment: 19 pages, 15 figures. To appear in A
A Population of Metal-Poor Galaxies with ~L* Luminosities at Intermediate Redshifts
We present new spectroscopy and metallicity estimates for a sample of 15
star-forming galaxies with redshifts in the range 0.29 - 0.42. These objects
were selected in the KPNO International Spectroscopic Survey via their strong
emission lines seen in red objective-prism spectra. Originally thought to be
intermediate-redshift Seyfert 2 galaxies, our new spectroscopy in the far red
has revealed these objects to be metal-poor star-forming galaxies. These
galaxies follow a luminosity-metallicity (L-Z) relation that parallels the one
defined by low-redshift galaxies, but is offset by a factor of more than ten to
lower abundances. The amount of chemical and/or luminosity evolution required
to place these galaxies on the local L-Z relation is extreme, suggesting that
these galaxies are in a very special stage of their evolution. They may be
late-forming massive systems, which would challenge the current paradigm of
galaxy formation. Alternatively, they may represent intense starbursts in
dwarf-dwarf mergers or a major infall episode of pristine gas into a
pre-existing galaxy. In any case, these objects represent an extreme stage of
galaxy evolution taking place at relatively low redshift.Comment: 6 pages, 3 figures; to appear in 10 April 2009 ApJ
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