HST 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

S. Toft; P. van Dokkum; M. Franx; I. Labbe; N. M. Forster Schreiber; S. Wuyts; T. Webb; G. Rudnick; A. Zirm; M. Kriek; P. van der Werf; J. P. Blakeslee; G. Illingworth; H. -W. Rix; C. Papovich; A. Moorwood

doi:10.1086/521810

arXiv · 0707.4484

HST 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

S. Toft·P. van Dokkum·M. Franx·I. Labbe·N. M. Forster Schreiber·S. Wuyts·T. Webb·G. Rudnick·A. Zirm·M. Kriek·P. van der Werf·J. P. Blakeslee·G. Illingworth·H. -W. Rix·C. Papovich·A. Moorwood

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Abstract

We present HST NICMOS+ACS and Spitzer IRAC+MIPS observations of 41 galaxies at 2<z<3.5 in the FIRES MS1054 field with red and blue rest-frame optical colors. About half of the galaxies are very compact (effective radii r_e < 1 kpc) at rest-frame optical wavelengths, the others are extended (1< r_e < 10 kpc). For reference, 1 kpc corresponds to 0.12 arcsec 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 r_e<2kpc. In the redshift range where MIPS 24 micron imaging is a sensitive probe of re-radiated dust emission (z<2.5), the 24 micron 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 z_f~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.

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S. Toft, P. van Dokkum, M. Franx, I. Labbe, N. M. Forster Schreiber, S. Wuyts, T. Webb, G. Rudnick, A. Zirm, M. Kriek, P. van der Werf, J. P. Blakeslee, G. Illingworth, H. -W. Rix, C. Papovich, A. Moorwood. 2007-07-31. HST 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. https://doi.org/10.1086/521810

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