The Population of B z K -selected ULIRGs at z ~ 2

Abstract

We investigate the multiwavelength emission of BzK -selected star-forming galaxies at z ~ 2 in the Great Observatories Origins Deep Survey (GOODS) North region. Most (82%) of the sources are individually detected at 24 μm in the Spitzer MIPS imaging, and one-fourth (26%) in the VLA radio data. Significant detections of the individually undetected objects are obtained through stacking in the radio, submillimeter, and X-ray domains. The typical star-forming galaxy with stellar mass ~10 11 M ☉ at z = 2 is an ultraluminous infrared galaxy (ULIRG), with L IR ~ (1-2) × 10 12 L ☉ and star formation rate SFR ≈ 200-300 M ☉ yr -1 , implying a comoving density of ULIRGs at z = 2 at least 3 orders of magnitude above the local one. SFRs derived from the reddening-corrected UV luminosities agree well, on average, with the longer wavelength estimates. The high 24 μm detection rate suggests a relatively large duty cycle for the BzK star-forming phase, which is consistent with the available independent measurements of the space density of passively evolving galaxies at z > 1.4. If the IMF at z = 2 is similar to the local one, and in particular if it is not top-heavy, this suggests that a substantial fraction of the high-mass tail (≳10 11 M ☉ ) of the galaxy stellar mass function was completed by z ≈ 1.4.