STRUCTURAL EVOLUTION OF EARLY-TYPE GALAXIES TO z = 2.5 IN CANDELS
- Max-Planck Institut fuer Astronomie, Koenigstuhl 17, D-69117 Heidelberg (Germany)
- UCO/Lick Observatory, Department of Astronomy and Astrophysics, University of California, Santa Cruz, CA 95064 (United States)
- Department of Astronomy, University of Michigan, 500 Church Street, Ann Arbor, MI 48109 (United States)
- Department of Physics and Astronomy, Colby College, Waterville, ME 04901 (United States)
- Max-Planck-Institut fuer Extraterrestrische Physik, Postfach 1312, Giessenbachstr., D-85741 Garching (Germany)
- Schools of Physics and Astronomy, University of Nottingham, University Park, Nottingham NG7 2RD (United Kingdom)
- Institute of Astro- and Particle Physics, University of Innsbruck, Technikerstrasse 25, A-6020 Innsbruck (Austria)
- Space Telescope Science Institute, 3700 San Martin Drive, Baltimore, MD 21218 (United States)
- INAF-Osservatorio di Roma, Via Frascati 33, I-00040 Monteporzio (Italy)
- Racah Institute of Physics, Hebrew University, Jerusalem 91904 (Israel)
Projected axis ratio measurements of 880 early-type galaxies at redshifts 1 < z < 2.5 selected from CANDELS are used to reconstruct and model their intrinsic shapes. The sample is selected on the basis of multiple rest-frame colors to reflect low star-formation activity. We demonstrate that these galaxies as an ensemble are dust-poor and transparent and therefore likely have smooth light profiles, similar to visually classified early-type galaxies. Similar to their present-day counterparts, the z > 1 early-type galaxies show a variety of intrinsic shapes; even at a fixed mass, the projected axis ratio distributions cannot be explained by the random projection of a set of galaxies with very similar intrinsic shapes. However, a two-population model for the intrinsic shapes, consisting of a triaxial, fairly round population, combined with a flat (c/a {approx} 0.3) oblate population, adequately describes the projected axis ratio distributions of both present-day and z > 1 early-type galaxies. We find that the proportion of oblate versus triaxial galaxies depends both on the galaxies' stellar mass, and-at a given mass-on redshift. For present-day and z < 1 early-type galaxies the oblate fraction strongly depends on galaxy mass. At z > 1, this trend is much weaker over the mass range explored here (10{sup 10} < M{sub *}/M{sub Sun} < 10{sup 11}), because the oblate fraction among massive (M{sub *} {approx} 10{sup 11} M{sub Sun }) was much higher in the past: 0.59 {+-} 0.10 at z > 1, compared to 0.20 {+-} 0.02 at z {approx} 0.1. When combined with previous findings that the number density and sizes of early-type galaxies substantially increase over the same redshift range, this can be explained by the gradual emergence of merger-produced elliptical galaxies, at the expense of the destruction of pre-existing disks that were common among their high-redshift progenitors. In contrast, the oblate fraction among low-mass early-type galaxies (log (M{sub *}/M{sub Sun }) < 10.5) increased toward the present, from z = 0 to 0.38 {+-} 0.11 at z > 1 to 0.72 {+-} 0.06 at z = 0. We speculate that this lower incidence of disks at early cosmic times can be attributed to two factors: low-mass, star-forming progenitors at z > 1 were not settled into stable disks to the same degree as at later cosmic times, and the stripping of gas from star-forming disk galaxies in dense environments is an increasingly important process at lower redshifts.
- OSTI ID:
- 22130970
- Journal Information:
- Astrophysical Journal, Vol. 773, Issue 2; Other Information: Country of input: International Atomic Energy Agency (IAEA); ISSN 0004-637X
- Country of Publication:
- United States
- Language:
- English
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