Ryan Leaman, Kim A. Venn, Alyson M. Brooks, Giuseppina Battaglia, Andrew A. Cole, Rodrigo A. Ibata, Mike J. Irwin, Alan W. McConnachie, J. Trevor Mendel, Eline Tolstoy
We present spectroscopic data for 180 red giant branch stars in the isolated
dwarf irregular galaxy WLM. Observations of the Calcium II triplet lines in
spectra of RGB stars covering the entire galaxy were obtained with FORS2 at the
VLT and DEIMOS on Keck II allowing us to derive velocities, metallicities, and
ages for the stars. With accompanying photometric and radio data we have
measured the structural parameters of the stellar and gaseous populations over
the full galaxy. The stellar populations show an intrinsically thick
configuration with $0.39 \leq q_{0} \leq 0.57$. The stellar rotation in WLM is
measured to be $17 \pm 1$ km s$^{-1}$, however the ratio of rotation to
pressure support for the stars is $V/\sigma \sim 1$, in contrast to the gas
whose ratio is seven times larger. This, along with the structural data and
alignment of the kinematic and photometric axes, suggests we are viewing WLM as
a highly inclined oblate spheroid. Stellar rotation curves, corrected for
asymmetric drift, are used to compute a dynamical mass of $4.3\pm
0.3\times10^{8} $M$_{\odot}$ at the half light radius ($r_{h} = 1656 \pm 49$
pc). The stellar velocity dispersion increases with stellar age in a manner
consistent with giant molecular cloud and substructure interactions producing
the heating in WLM. Coupled with WLM's isolation, this suggests that the
extended vertical structure of its stellar and gaseous components and increase
in stellar velocity dispersion with age are due to internal feedback, rather
than tidally driven evolution. These represent some of the first observational
results from an isolated Local Group dwarf galaxy which can offer important
constraints on how strongly internal feedback and secular processes modulate SF
and dynamical evolution in low mass isolated objects.
View original:
http://arxiv.org/abs/1202.4474
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