Optical Spectroscopy of K-selected Extremely Red Galaxies

Abstract

We have obtained spectroscopic redshifts for 24 red galaxies from a sample with median Ks=18.7 and F814W - Ks > 4, using the Keck telescope. These EROshave high resolution morphologies from HST (Yan & Thompson 2003). Among the 24 redshifts, the majority (92%) are at $0.9<z<1.5$. We derived the rest-frame J-band luminosity function at $z_{median}=1.14$. Our result suggests that the luminosity evolution between bright EROs at $z\sim 1$ and the present-day $>$L${}^{\ast }$ massive galaxies is at most about 0.7 magnitude. Combining the morphologies and deep spectroscopy revealed the following properties: (1) 86% of the spectra have absorption features from old stars, suggesting that the dominant stellar populations seen in the rest-frame UV are old stars. 50% of the sources have pure absorption lines, while the remaining 50% have emission lines, indicating recent star formation. We conclude that the color criterion for EROs is very effective in selecting old stellar populations at $z\sim 1$, and a large fraction of these systems with prominent old stellar populations also have recent star formation. (2) The 12 emission line systems have the same number of disk and bulge galaxies as in the remaining 12 pure absorption line systems. We conclude that spectral classes do not have a simple, direct correspondence with morphological types. (3) Three EROs could be isolated, pure passively evolving early-type galaxies at $z\sim 1$. This implies that only a small fraction (10%--15%) of early-type galaxies are formed in a rapid burst of star formation at high redshifts and evolved passively since then. (Abridged).

27 pages, 8 figures. Accepted for publication in Astronomical Journal, issue March 2004

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• The Las Campanas Infra-red Survey. V. Keck Spectroscopy of a large sample of Extremely Red Objects
• An H-band survey of the Herschel Deep Field
• Morphologies of Two Massive Old Galaxies at z ~ 2.5
• Observational tests of the evolution of spheroidal galaxies
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• A LABOCA survey of the Extended Chandra Deep Field South - submillimeter properties of near-IR selected galaxies
• The Clustering of Extragalactic Extremely Red Objects
• Deep GMOS Spectroscopy of Extremely Red Galaxies in GOODS-South: Ellipticals, Mergers and Red Spirals at 1<z<2
• Spitzer Observations of the Prototypical Extremely Red Objects HR10 and LBDS53W091: Separating Dusty Starbursts from Old Elliptical Galaxies
• Number Counts of Bright Extremely Red Objects: Evolved Massive Galaxies at z~1
• The Serendipitous XMM-Newton Cluster Athens Survey (SEXCLAS): Sample selection and the cluster log N - log S
• Galaxy Collisions - Dawn of a New Era
• Stellar Populations of Luminous Evolved Galaxies at z~1.5
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• Properties of Extremely Red Objects in an Overdense Region
• The nature of the red disk-like galaxies at high redshift: dust attenuation and intrinsically red stellar populations
• Optical to Near-IR Spectrum of a Massive Evolved Galaxy at z = 1.26
• Morphologies in a Cluster of Extremely Red Galaxies with Old Stellar Populations at z=1.34
• A massive disk galaxy at z>3 along the sightline of QSO 1508+5714