Hubble Space Telescope and Spitzer Imaging of Red and Blue Galaxies at z ~ 2.5: A Correlation between Size and Star Formation Activity from Compact Quiescent Galaxies to Extended Star-forming Galaxies
Abstract
We present HST NICMOS+ACS and Spitzer IRAC+MIPS observations of 41 galaxies at 2<z<3.5 in the FIRES MS 1054 field with red and blue rest-frame optical colors. About half of the galaxies are very compact (effective radii re<1 kpc) at rest-frame optical wavelengths; the others are extended (1 kpc<re<10 kpc). For reference, 1 kpc corresponds to 0.12" at z=2.5 in the adopted cosmology. We separate actively star-forming galaxies from quiescent galaxies by modeling their rest-frame UV-NIR SEDs. The star-forming galaxies span the full range of sizes, while the quiescent galaxies all have re<2 kpc. In the redshift range where MIPS 24 μm imaging is a sensitive probe of reradiated dust emission (z<2.5), the 24 μm fluxes confirm that the light of the small quiescent galaxies is dominated by old stars, rather than dust-enshrouded star formation or AGN activity. The inferred surface mass densities and velocity dispersions for the quiescent galaxies are very high compared to those in local galaxies. The galaxies follow a Kormendy relation (between surface brightness and size) with approximately the same slope as locally, but shifted to brighter surface brightnesses, consistent with a mean stellar formation redshift of zf~5. This paper demonstrates a direct relation between star formation activity and size at z~2.5 and the existence of a significant population of massive, extremely dense, old stellar systems without readily identifiable counterparts in the local universe.
Based on observations made with the NASA/ESA Hubble Space Telescope, which is operated by the Association of Universities for Research in Astronomy, Inc., under NASA contract NAS5-26555 observations made with the Spitzer Space Telescope, which is operated by the Jet Propulsion Laboratory, California Institute of Technology under NASA contract 1407; and observations collected at the European Southern Observatory, Paranal, Chile (ESO Program 164.O-0612).- Publication:
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The Astrophysical Journal
- Pub Date:
- December 2007
- DOI:
- 10.1086/521810
- arXiv:
- arXiv:0707.4484
- Bibcode:
- 2007ApJ...671..285T
- Keywords:
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- Galaxies: Evolution;
- Galaxies: Formation;
- Galaxies: Fundamental Parameters;
- Galaxies: High-Redshift;
- Galaxies: Structure;
- Infrared: Galaxies;
- Astrophysics
- E-Print:
- Accepted for publication in ApJ