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Title:
Morphologies and Color Gradients of Luminous Evolved Galaxies at z ~ 1.5
Authors:
McGrath, Elizabeth J.; Stockton, Alan; Canalizo, Gabriela; Iye, Masanori; Maihara, Toshinori
Affiliation:
AA(Institute for Astronomy, University of Hawaii, 2680 Woodlawn Dr., Honolulu, HI 96822; Currently at the University of California Observatories/Lick Observatory, Department of Astronomy and Astrophysics, University of California at Santa Cruz, 1156 High Street, Santa Cruz, CA 95064.), AB(Institute for Astronomy, University of Hawaii, 2680 Woodlawn Dr., Honolulu, HI 96822), AC(Department of Physics and Astronomy, University of California, Riverside, CA 92521), AD(Optical and Infrared Astronomy Division, National Astronomical Observatory of Japan, Mitaka, Tokyo 181-8588, Japan), AE(Department of Astronomy, Kyoto University, Kitashirakawa-Oiwake-cho, Sakyo-ku, Kyoto 606-8502, Japan)
Publication:
The Astrophysical Journal, Volume 682, Issue 1, pp. 303-318. (ApJ Homepage)
Publication Date:
07/2008
Origin:
UCP
ApJ Keywords:
Galaxies: Evolution, Galaxies: Formation, Galaxies: High-Redshift
DOI:
10.1086/589631
Bibliographic Code:
2008ApJ...682..303M

Abstract

We have examined in detail the morphologies of seven z~1.5 passively evolving luminous red galaxies using high-resolution HST NICMOS and ACS imaging data. Almost all of these galaxies appear to be relaxed systems, with smooth morphologies at both rest-frame UV and visible wavelengths. Previous results from spectral synthesis modeling favor a single burst of star formation more than 1 Gyr before the observed epoch. The prevalence of old stellar populations, however, does not correlate exclusively with early-type morphologies as it does in the local universe; the light profiles for some of these galaxies appear to be dominated by massive exponential disks. This evidence for massive old disks, along with the apparent uniformity of stellar age across the disk, suggests formation by a mechanism better described as a form of monolithic collapse than as a hierarchical merger. These galaxies could not have undergone a single major merging event since the bulk of their stars were formed, more than 1 Gyr earlier. There is at least one case, however, that appears to be undergoing a ``dry merger,'' which may be an example of the process that converts these unusual galaxies into the familiar spheroids that dominate galaxies comprising old stellar populations at the present epoch.

Based on observations made with the NASA/ESA Hubble Space Telescope, obtained at the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Inc., under NASA contract NAS 5-26555. These observations are associated with program GO-10418.

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