GMOS SV program 66

We propose GMOS deep imaging and multi-slit spectral observations of faint galaxies detected in the vicinity of the QSOs UM 225 (Q0013-004, z_em = 2.083) and Q0201+365 (z_em = 2.912), both of which exhibit complicated absorption-line spectra with several intervening metal-line absorbers evident at various redshifts. Each of these spectra harbors at least one damped Ly-alpha system, which are presumed to originate within the interstellar media of high-redshift galaxies. We propose to study the distribution of galaxies around each of these QSOs in an effort to study and characterize the galaxies responsible for this high column density, low ionization absorption. The imaging of damped Ly-alpha absorbers has been a difficult challenge, even at much lower redshifts, and we do not expect to be able to resolve the absorber from the background QSO with GMOS imaging - we have proposed for higher resolution Hokupa'a + Gemini imaging for that purpose. In this proposal we will image a larger area surrounding the QSOs and obtain optical spectra of all galaxies detected down to a limiting magnitude of R ~ 23. These data will identify low-redshift galaxies which coincidentally lie along the line of sight and are not associated with the damped Ly-alpha absorber. We will also identify, based on the optical spectra plus the H+K' - R color for those galaxies in both the Hokupa'a and GMOS fields of view, high-redshift galaxy candidates suitable for follow-up near-IR spectroscopy. Our goal is to provide redshifts for all galaxies surrounding UM224 and Q0201+365 in an effort to characterize the potential cluster (and formation) environment of these high-redshift damped Ly-alpha absorbers, two of which appear to have unusually neutral, thereby presumably cool and dusty, interstellar media which mimic the absorption properties of galaxy disks.

We propose to construct MOS masks based on deep GMOS r-band imaging. We wish to get spectra of as many galaxies in the field surrounding the QSO as possible. The DLA itself is expected to not be resolved from the QSO with GMOS, yet we expect there will be group or cluster members in the field. We propose to use the R400 grating with central wavelengths of 700nm to obtain spectra of these potential galaxy group members. The DLA for UM224 is at a redshift of 1.975, and is a particularly interesting system because its absorption spectrum shows both C I and molecular hydrogen features. In addition to the DLA, there are metal absorption systems (hence expected galaxies and possible groups or clusters) at redshifts of 1.7, 1.6, and 0.45. The DLA toward 0201+365 is at a redshift of 2.46 and also probably exhibits C I absorption (not as confident a detection). There are additional systems at redshifts of 1.5, 1.7, 1.9, 2.0, 2.8 and 0.3. A third potential QSO target is 0551-366 which has clear detections from ESO UVES of both C I and molecular hydrogen, however it may be more suitable for observations with GMOS-South. None of these three QSOs have been the focus of targeted imaging/spectroscopic campaigns. This would be a good SV program to demonstrate the MOS mode, the data would be of interest to high redshift galaxy types as well as people studying galaxy clustering and evolution. And perhaps we will find the DLA is not so on top of the QSO as everyone assumes (longshot).