We present the results of a detailed study of the interstellar medium ( ISM ) of MS 1512 - cB58 , an \sim L ^ { \ast } Lyman break galaxy at z = 2.7276 , based on new spectral observations obtained with the Echelle Spectrograph and Imager on the Keck II telescope at 58 km s ^ { -1 } resolution .
We focus in particular on the chemical abundances and kinematics of the interstellar gas deduced from the analysis of 48 ultraviolet absorption lines , at rest wavelengths between 1134 and 2576 Å , due to elements from H to Zn .
Our main findings are as follows .
Even at this relatively early epoch , the ISM of this galaxy is already highly enriched in elements released by Type II supernovae ; the abundances of O , Mg , Si , P , and S are all \sim 2 / 5 of their solar values .
In contrast , N and the Fe-peak elements Mn , Fe , and Ni are underabundant by a factor of \sim 3 .
Based on current ideas of stellar nucleosynthesis , these results can be understood if most of the metal enrichment in cB58 has taken place within the last \sim 300 Myr , the timescale for the release of N from intermediate mass stars .
Such a young age is consistent with the UV-optical spectral energy distribution .
Thus , cB58 appears to be an example of a galaxy in the process of converting its gas into stars on a few dynamical timescales—quite possibly we are witnessing the formation of a galactic bulge or an elliptical galaxy .
The energetic star formation activity has stirred the interstellar medium to high velocities ; the strongest absorption lines span a velocity interval of \sim 1000 km s ^ { -1 } .
The net effect is a bulk outflow of the ISM at a speed of \sim 255 km s ^ { -1 } and at a rate which exceeds the star formation rate .
It is unclear whether this gas will be lost or retained by the galaxy .
On the one hand , the outflow probably has sufficient energy to escape the potential well of cB58 , for which we derive a baryonic mass of \sim 10 ^ { 10 } M _ { \odot } .
On the other hand , at least some of the elements manufactured by previous generations of stars must have mixed efficiently with the ambient , neutral , ISM to give the high abundances we measure .
We point out that the chemical and kinematic properties of cB58 are markedly different from those of most damped Lyman \alpha systems at the same redshift .