Metals and a Search for Molecules in the Distant Universe: Magellan MIKE
  Observations of sub-DLAs at 2<z<3
  We present abundance measurements of the elements Zn, S, O, C, Si and Fe for
four sub-DLAs at redshifts ranging from z=2.173 to z=2.635 using observations
from the MIKE spectrograph on the Magellan telescope to constrain the chemical
enrichment and star formation of gas-rich galaxies. Using weakly depleted
elements O, S, and or Zn, we find the metallicities after the photoionization
corrections to be [S/H]=-0.50\pm0.11, [O/H]>-0.84, [O/H]=-1.27\pm0.12, and
[Zn/H]=+0.40\pm0.12 for the absorbers at z=2.173, 2.236, 2.539, and 2.635,
respectively. Moreover, we are able to put constraints on the electron
densities using the fine structure lines of C II* and Si II* for two of the
sub-DLAs. We find that these values are much higher than the median values
found in DLAs in the literature. Furthermore, we estimate the cooling rate
lc=1.20\times10-26 erg s-1 per H atom for an absorber at z=2.173, suggesting
higher star formation rate density in this sub-DLA than the typical star
formation rate density for DLAs at similar redshifts. We also study the
metallicity versus velocity dispersion relation for our absorbers. Most of the
absorbers follow the trend one can expect from the mass versus metallicity
relation for sub-DLAs in the literature. Finally, we are able to put limits on
the molecular column density from the non detections of various strong lines of
CO molecules. We estimate 3\sigma upper limits of log N(CO,J=0)<13.87, log
N(CO,J=0)<13.17, and log N(CO,J=0)<13.08, respectively, from the non-detections
of absorption from the J=0 level in the CO AX 0-0, 1-0, and 2-0 bands near
1544, 1510, and 1478\AA.
