Metals and Molecules in the Distant Universe: Magellan MIKE Observations of Gas-rich Galaxies at 2
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 in order to constrain the chemical enrichment and star formation of gas-rich galaxies. Using weakly depleted elements such as O, S, and or Zn, we find the metallicities after the photoionization corrections to be [S/H]=-0.50\pm0.11, [O/H]=-0.70\pm0.17, [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=1.20X10-26 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 and compare the values with those from the literature. Most of the absorbers follow the trend one can expect from the mass versus metallicity relation for sub-DLAs. 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 NCOJ0<13.68 and log NCOJ0<14.05, respectively, from the non-detections of COJ0 {\lambda}1477.6 and COJ0 {\lambda}1544.4 lines.