MAMBO 1.2 mm Observations of B z K -selected Star-forming Galaxies at z ~ 2

Abstract

We present MAMBO 1.2 mm observations of five BzK-preselected vigorous starburst galaxies at z~2. Two of these were detected at more than 99.5% confidence levels, with 1.2 mm fluxes around 1.5 mJy. These millimeter fluxes imply vigorous activity with star formation rates (SFRs) of ~500-1500 Msolar yr-1, which were also confirmed by detections at 24 μm with the Multiband Imaging Photometer on Spitzer (MIPS). The two detected galaxies are the ones in the sample with the highest SFRs estimated from the rest-frame UV, and their far-IR-derived and UV-derived SFRs agree reasonably well. This is different from local ultraluminous infrared galaxies (ULIRGs) and high-z submillimeter/millimeter-selected galaxies, for which the UV is reported to underestimate SFRs by factors of 10-100, but similar to the average BzK ULIRG at z~2. The two galaxies detected at 1.2 mm are brighter in K than the typical NIR counterparts of MAMBO and SCUBA sources, implying a significantly different K-band-to-submillimeter/millimeter flux ratio as well. This suggests a scenario in which z~2 galaxies, after their rapid (sub)millimeter-bright phase that is opaque to optical/UV light, evolve into a longer lasting phase of K-band-bright and massive objects. Targeting the most UV-active BzK galaxies could yield substantial detection rates at submillimeter/millimeter wavelengths. Based on observations carried out with the IRAM 30 m Telescope at Pico Veleta. IRAM is supported by INSU/CNRS (France), MPG (Germany), and IGN (Spain). Also based on ESO observations (program IDs 072.A-0506 and 075.A-0439) and on Subaru observations (programs S02B-101 and S04A-081), and on observations made with the Spitzer Space Telescope, which is operated by the JPL, Caltech, under a contract with NASA.