Stellar Populations of Luminous Evolved Galaxies at z~1.5

Abstract

Observational evidence has been mounting over the past decade that at least some luminous (~2 L*) galaxies have formed nearly all of their stars within a short period of time only 1-2x10^9 years after the Big Bang. These are examples of the first major episodes of star formation in the Universe and provide insights into the formation of the earliest massive galaxies. We have examined in detail the stellar populations of six z~1.5 galaxies that appear to be passively evolving, using both ground and space-based photometry covering rest-frame UV to visible wavelengths. In addition, we have obtained medium-resolution spectroscopy for five of the six galaxies, covering the rest-frame UV portion of the spectrum. Spectral synthesis modeling for four of these galaxies favors a single burst of star formation more than 1 Gyr before the observed epoch. The other two exhibit slightly younger ages with a higher dust content and evidence for a small contribution from either recent star formation or active nuclei. The implied formation redshifts for the oldest of these sources are consistent with previous studies of passive galaxies at high redshift, and improved stellar modeling has shown these results to be quite robust. It now seems clear that any valid galaxy formation scenario must be able to account for these massive (2x10^11 M_sun) galaxies at very early times in the Universe.

10 pages, 3 figures (2 in color), accepted for publication in ApJ

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• The COSMOS-WIRCam near-infrared imaging survey: I: BzK selected passive and star forming galaxy candidates at z>1.4
• Red Nuggets at High Redshift: Structural Evolution of Quiescent Galaxies Over 10 Gyr of Cosmic History
• Spectroscopic Confirmation Of An Extreme Starburst At Redshift 4.547
• Central mass-to-light ratios and dark matter fractions in early-type galaxies
• A submillimetre galaxy at z=4.76 in the LABOCA survey of the Extended Chandra Deep Field South
• The population of early-type galaxies at 1<z<2 - New clues on their formation and evolution
• The Rise of Massive Red Galaxies: the color-magnitude and color-stellar mass diagrams for z < ~2 from the MUltiwavelength Survey by Yale-Chile (MUSYC)
• Morphologies and Color Gradients of Luminous Evolved Galaxies at z~1.5
• The fate of high-redshift massive compact galaxies
• The impact of nebular emission on the broadband fluxes of high-redshift galaxies
• The Evolution of Field Early-Type Galaxies in the FDF and WHDF
• Red-Sequence Galaxies at High Redshift by the COMBO-17+4 Survey