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Session 30 - Galaxy Evolution I.
Oral session, Monday, January 15
1st Floor, La Villita Assembly Building

[30.05] The Discovery of a Young, Apparently Normal Disk Galaxy at z = 3.15

S. G. Djorgovski, M. A. Pahre (Caltech), J. Bechtold (U. Arizona), R. Elston (NOAO)

We report on the discovery of an apparently normal disk galaxy, associated with a damped Ly\alpha absorber at z = 3.155, in the field of the quasar 2233+131. The initial observations were obtained with the W.M. Keck telescope at Mauna Kea. This object was detected in Ly\alpha emission at essentially the same redshift as the previously known absorber, with a restframe velocity shift of only \sim 200 km/s. It is also detected in the optical (restframe FUV) continuum, with V \approx 25^m, which is consistent with a luminous, star-forming disk galaxy at that redshift. It is seen 2.5 arcsec in projection from the background quasar, corresponding to the restframe projected separation of \sim 15 h^-1 kpc for Ømega_0 = 0.2. Both the projected spatial extent and the restframe velocity shift are typical of normal disk galaxies, and support the generally believed interpretation of damped Ly\alpha absorbers as disk galaxies at high redshifts. This is the first time that such an absorber galaxy (rather than a clustered companion thereof) has been unambiguously detected through its line and continuum emission. There are no high-ionization lines in the spectrum, suggesting that the observed Ly\alpha emission is powered by active star formation in a young disk galaxy. At this redshift, the age of the universe is only \sim 10 - 15% of its present age, and thus this galaxy can be plausibly interpreted as a proto-disk galaxy, perhaps a progenitor of a Milky Way-like object today. At the meeting we will present the results of the follow-up IR imaging and spectroscopy at IRTF, Keck, and telescopes at Kitt Peak.

Program listing for Monday