ALMA galaxy properties in the COSMOS survey field

We also develop a physical basis and empirical calibration (with 72 low-z and z~2 galaxies) for using the dust continuum as a quantitative probe of ISM masses. The galaxies with the highest star formation rates (SFRs) at <z>=2.2 and 4.4 have gas masses up to 100 times that of the Milky Way and gas mass fractions reaching 50%-80%, i.e., gas masses 1-4x their stellar masses.

We find a single high-z star formation law: SFR=35 M_mol_^0.89^x(1+z)_z=2_^0.95^x(sSFR)_MS_^0.23^ M_{sun}_/yr - an approximately linear dependence on the ISM mass and an increased star formation efficiency per unit gas mass at higher redshift. Galaxies above the main sequence (MS) have larger gas masses but are converting their ISM into stars on a timescale only slightly shorter than those on the MS; thus, these "starbursts" are largely the result of having greatly increased gas masses rather than an increased efficiency of converting gas to stars.