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

• Published in: The Astrophysical journal 2007-11, Vol.670 (1), p.156-172
• Main 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
• Format: Article
• Language: English
• ISSN: 0004-637X
• DOI: 10.1086/521818

Examining a sample of massive galaxies at 1.4 < z < 2.5 with [unk] < 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 similar to 2 galaxies with moderate luminosities ( [unk] < 10 super(11) L [unk]), 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 [unk] 10 super(11) L [unk], 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 mu m-detected galaxies. For a given mass, the SFR at z = 2 was larger by a factor of similar to 4 and similar to 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 ( [unk]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.