Multiwavelength Study of Massive Galaxies at z~2. I. Star Formation and Galaxy Growth

November 2007 • 2007ApJ...670..156D

Authors • Daddi, E. • Dickinson, M. • Morrison, G. • Chary, R. • Cimatti, A. • Elbaz, D. • Frayer, D. • Renzini, A. • Pope, A. • Alexander, D. M. • Bauer, F. E. • Giavalisco, M. • Huynh, M. • Kurk, J. • Mignoli, M.

Abstract • Examining a sample of massive galaxies at 1.4<z<2.5 with K_Vega<22 from GOODS, we compare photometry from Spitzer at mid- and far-IR to submillimeter, radio, and rest-frame UV wavelengths, to test the agreement between different tracers of star formation rates (SFRs) and to explore the implications for galaxy assembly. For z~2 galaxies with moderate luminosities (L_8μm<10¹¹ L_solar), we find that the SFR can be estimated consistently from the multiwavelength data based on local luminosity correlations. However, 20%-30% of massive galaxies, and nearly all those with L_8μm>10¹¹ L_solar, show a mid-IR excess that is likely due to the presence of obscured active nuclei, as shown in a companion paper. There is a tight and roughly linear correlation between stellar mass and SFR for 24 μm-detected galaxies. For a given mass, the SFR at z=2 was larger by a factor of ~4 and ~30 relative to that in star-forming galaxies at z=1 and 0, respectively. Typical ultraluminous infrared galaxies (ULIRGs) at z=2 are relatively ``transparent'' to ultraviolet light, and their activity is long lived (>~400 Myr), unlike that in local ULIRGs and high-redshift submillimeter-selected galaxies. ULIRGs are the common mode of star formation in massive galaxies at z=2, and the high duty cycle suggests that major mergers are not the dominant trigger for this activity. Current galaxy formation models underpredict the normalization of the mass-SFR correlation by about a factor of 4 and the space density of ULIRGs by an order of magnitude but give better agreement for z>1.4 quiescent galaxies.

Links

View on ADS

IPAC Authors
(alphabetical)

Ranga-Ram Chary

Senior Scientist