PHIBSS: MOLECULAR GAS CONTENT AND SCALING RELATIONS IN<i>z</i>∼ 1-3 MASSIVE, MAIN-SEQUENCE STAR-FORMING GALAXIES

Abstract

We present PHIBSS, the IRAM Plateau de Bure high-z blue sequence CO 3-2\nsurvey of the molecular gas properties in normal star forming galaxies (SFGs)\nnear the cosmic star formation peak. PHIBSS provides 52 CO detections in two\nredshift slices at z~1.2 and 2.2, with log(M*(M_solar))&gt;10.4 and\nlog(SFR(M_solar/yr))&gt;1.5. Including a correction for the incomplete coverage of\nthe M*-SFR plane, we infer average gas fractions of ~0.33 at z~1.2 and ~0.47 at\nz~2.2. Gas fractions drop with stellar mass, in agreement with cosmological\nsimulations including strong star formation feedback. Most of the z~1-3 SFGs\nare rotationally supported turbulent disks. The sizes of CO and UV/optical\nemission are comparable. The molecular gas - star formation relation for the\nz=1-3 SFGs is near-linear, with a ~0.7 Gyrs gas depletion timescale; changes in\ndepletion time are only a secondary effect. Since this timescale is much less\nthan the Hubble time in all SFGs between z~0 and 2, fresh gas must be supplied\nwith a fairly high duty cycle over several billion years. At given z and M*,\ngas fractions correlate strongly with the specific star formation rate. The\nvariation of specific star formation rate between z~0 and 3 is mainly\ncontrolled by the fraction of baryonic mass that resides in cold gas.\n