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Keck DEIMOS Spectroscopy of a GALEX UV-Selected Sample from the Medium Imaging Survey
We report results from a pilot program to obtain spectroscopy forobjects detected in the Galaxy Evolution Explorer (GALEX) Medium ImagingSurvey (MIS). Our study examines the properties of galaxies detected byGALEX fainter than the Sloan Digital Sky Survey (SDSS) spectroscopicsurvey. This is the first study to extend the techniques of Salim andcoworkers to estimate stellar masses, star formation rates (SFRs), andthe b (star formation history) parameter for star-forming galaxies outto z~0.7. We obtain redshifts for 50 GALEX MIS sources reaching NUV=23.9(AB mag) having counterparts in the SDSS Data Release 4 (DR4). Of oursample, 43 are star-forming galaxies with z<0.7, 3 have emission-lineratios indicative of active galactic nuclei with z<0.7, and 4 objectswith z>1 are QSOs, 3 of which are not previously cataloged. Wecompare our sample to a much larger sample of ~50,000 matched GALEX/SDSSgalaxies with SDSS spectroscopy; while our survey is shallow, theoptical counterparts to our sources reach ~3 mag fainter in SDSS r thanthe SDSS spectroscopic sample. We use emission-line diagnostics for thegalaxies to determine that the sample contains mostly star-forminggalaxies. The galaxies in the sample populate the blue sequence in theNUV-r versus Mr color-magnitude diagram. The derived stellarmasses of the galaxies range from 108 to 1011Msolar, and derived SFRs are between 10-1 and102 Msolar yr-1. Our sample has SFRs,luminosities, and velocity dispersions that are similar to the samplesof faint compact blue galaxies studied previously in the same redshiftrange by Koo and collaborators, Guzmán and collaborators, andPhillips and collaborators. However, our sample is ~2 mag fainter insurface brightness than the compact blue galaxies. We find that the starformation histories for a majority of the galaxies are consistent with arecent starburst within the last 100 Myr.Some of the data presented herein were obtained at the W. M. KeckObservatory, which is operated as a scientific partnership among theCalifornia Institute of Technology, the University of California, andthe National Aeronautics and Space Administration. The Observatory wasmade possible by the generous financial support of the W. M. KeckFoundation.
| Improved Astrometry and Photometry for the Luyten Catalog. II. Faint Stars and the Revised Catalog
We complete construction of a catalog containing improved astrometry andnew optical/infrared photometry for the vast majority of NLTT starslying in the overlap of regions covered by POSS I and by the secondincremental Two Micron All Sky Survey (2MASS) release, approximately 44%of the sky. The epoch 2000 positions are typically accurate to 130 mas,the proper motions to 5.5 mas yr-1, and the V-J colors to0.25 mag. Relative proper motions of binary components are measured to 3mas yr-1. The false-identification rate is ~1% for11<~V<~18 and substantially less at brighter magnitudes. Theseimprovements permit the construction of a reduced proper-motion diagramthat, for the first time, allows one to classify NLTT stars intomain-sequence (MS) stars, subdwarfs (SDs), and white dwarfs (WDs). We inturn use this diagram to analyze the properties of both our catalog andthe NLTT catalog on which it is based. In sharp contrast to popularbelief, we find that NLTT incompleteness in the plane is almostcompletely concentrated in MS stars, and that SDs and WDs are detectedalmost uniformly over the sky δ>-33deg. Our catalogwill therefore provide a powerful tool to probe these populationsstatistically, as well as to reliably identify individual SDs and WDs.
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