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The Kinematic Composition of MgII Absorbers
The study of galaxy evolution using quasar absorption lines requires an
understanding of what components of galaxies and their surroundings are
contributing to the absorption in various transitions. This paper considers the
kinematic composition of the class of 0.4 < z < 1.0 MgII absorbers,
particularly addressing the question of what fraction of this absorption is
produced in halos and what fraction arises from galaxy disks. We design models
with various fractional contributions from radial infall of halo material and
from a rotating thick disk component. We generate synthetic spectra from lines
of sight through model galaxies and compare the resulting ensembles of MgII
profiles with the 0.4 < z < 1.0 sample observed with HIRES/Keck. We apply a
battery of statistical tests and find that pure disk and pure halo models can
be ruled out, but that various models with rotating disk and infall/halo
contributions can produce an ensemble that is nearly consistent with the data.
A discrepancy in all models that we considered requires the existence of a
kinematic component intermediate between halo and thick disk. The variety of
MgII profiles can be explained by the gas in disks and halos of galaxies not
very much different than galaxies in the local Universe.
In any one case there is considerable ambiguity in diagnosing the kinematic
composition of an absorber from the low ionization high resolution spectra
alone. Future data will allow galaxy morphologies, impact parameters, and
orientations, FeII/MgII of clouds, and the distribution of high ionization gas
to be incorporated into the kinematic analysis. Combining all these data will
permit a more accurate diagnosis of the physical conditions along the line of
sight through the absorbing galaxy.Comment: 34 pages including 14 postscript figures; Accepted by the
Astrophysical Journal; URL http://www.astro.psu.edu/users/cwc/pubs.htm
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