paper

Spectroscopic Confirmation of a Population of Normal Star-Forming Galaxies at Redshifts z>3

arXiv:astro-ph/9602024 · doi:10.1086/310029

Abstract

We report the discovery of a substantial population of star--forming galaxies at $3.0 \simlt z \simlt 3.5$. These galaxies have been selected using color criteria sensitive to the presence of a Lyman continuum break superposed on an otherwise very blue far-UV continuum, and then confirmed with deep spectroscopy on the W. M. Keck telescope. The surface density of galaxies brighter than R=25 with 3 < z < 3.5 is galaxies arcmin, approximately 1.3\% of the deep counts at these magnitudes; this value applies both to ``random'' fields and to fields centered on known QSOs. The corresponding co-moving space density is approximately half that of luminous ($L \simgt L^{\ast}$) present--day galaxies. Our sample of galaxies is large enough that we can begin to detail the spectroscopic characteristics of the population as a whole. The spectra of the galaxies are remarkably similar to those of nearby star-forming galaxies, the dominant features being strong low--ionization interstellar absorption lines and high--ionization stellar lines, often with P-Cygni profiles characteristic of Wolf-Rayet and O--star winds. Lyman emission is generally weak ( Å rest equivalent width) and is absent for >50% of the galaxies. The star formation rates, measured directly from the far-UV continua, lie in the range 4-25 M$\sun$ yr for . Together with the morphological properties of the galaxy population, which we discuss in a companion paper (Giavalisco \et 1996), all of these findings strongly suggest that we have identified the high-redshift counterparts of the spheroid component of present--day luminous galaxies. In any case, it is clear that massive galaxy formation was already well underway by . (shortened abstract). arch-ive/yymmnnn

To be published in ApJ Letters, 12 pages, AAS Latex, including 2 figures. Also available at ftp://astro.caltech.edu/users/ccs/zg3spec.tar.gz

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