ALMA Cycle 2 observations of the long wavelength dust emission in 180 star-forming (SF) galaxies are used to investigate the evolution of ISM masses at z = 1 to 6.4. The ISM masses exhibit strong increases from z = 0 to $rm <z>$ = 1.15 and further to
$rm <z>$ = 2.2 and 4.8, particularly amongst galaxies above the SF galaxy main sequence (MS). The galaxies with highest SFRs at $rm <z>$ = 2.2 and 4.8 have gas masses 100 times that of the Milky Way and gas mass fractions reaching 50 to 80%, i.e. gas masses 1 - 4$times$ their stellar masses. For the full sample of galaxies, we find a single, very simple SF law: $rm SFR propto M_{rm ISM}^{0.9}$, i.e. a `linear dependence on the ISM mass -- on and above the MS. Thus, the galaxies above the MS are converting their larger ISM masses into stars on a timescale similar to those on the MS. At z $> 1$, the entire population of star-forming galaxies has $sim$5 - 10$times$ shorter gas depletion times ($sim0.2$ Gyr) than galaxies at low redshift. These {bf shorter depletion times are due to a different, dominant mode of SF in the early universe} -- dynamically driven by compressive, high dispersion gas motions and/or galaxy interactions. The dispersive gas motions are a natural consequence of the extraordinarily high gas accretion rates which must occur to maintain the prodigious SF.
We report ALMA Band 7 (350 GHz) imaging at 0.4 - 0.6arcsec resolution and Band 9 (696 GHz) at ~0.25arcsec resolution of the luminous IR galaxies Arp 220 and NGC 6240. The long wavelength dust continuum is used to estimate ISM masses for Arp 220 East,
West and NGC 6240 of 1.9, 4.2 and 1.6x10^9 msun within radii of 69, 65 and 190 pc. The HCN emission was modeled to derive the emissivity distribution as a function of radius and the kinematics of each nuclear disk, yielding dynamical masses consistent with the masses and sizes derived from the dust emission. In Arp 220, the major dust and gas concentrations are at radii less than 50 pc in both counter-rotating nuclear disks. The thickness of the disks in Arp 220estimated from the velocity dispersion and rotation velocities are 10-20 pc and the mean gas densities are n_H2 ~10^5 cm^-3 at R < 50 pc. We develop an analytic treatment for the molecular excitation (including photon trapping), yielding volume densities for both the HCN and CS emission with n_H2 ~2x10^5 cm^-3. The agreement of the mean density from the total mass and size with that required for excitation suggests that the volume is essentially filled with dense gas, i.e. it is not cloudy or like swiss cheese.
The use of submm dust continuum emission to probe the mass of interstellar dust and gas in galaxies is empirically calibrated using samples of local star forming galaxies, Planck observations of the Milky Way and high redshift submm galaxies (SMGs).
All of these objects suggest a similar calibration, strongly supporting the view that the Rayleigh-Jeans (RJ) tail of the dust emission can be used as an accurate and very fast probe of the ISM in galaxies. We present ALMA Cycle 0 observations of the Band 7 (350 GHz) dust emission in 107 galaxies from z = 0.2 to 2.5. Three samples of galaxies with a total of 101 galaxies were stellar mass-selected from COSMOS to have $M_* simeq10^{11}$msun: 37 at z$sim0.4$, 33 at z$sim0.9$ and 31 at z$=2$. A fourth sample with 6 IR luminous galaxies at z = 2 was observed for comparison with the purely mass-selected samples. From the fluxes detected in the stacked images for each sample, we find that the ISM content has decreased a factor $sim 6$ from $1 - 2 times 10^{10}$msun at both z = 2 and 0.9 down to $sim 2 times 10^9$msun at z = 0.4. The IR luminous sample at z = 2 shows a further $sim 4$ times increase in M$_{ISM}$ compared to the equivalent non-IR bright sample at the same redshift. The gas mass fractions are $sim 2pm0.5, 12pm3, 14pm2 ~rm{and} ~53pm3$ $%$ for the four subsamples (z = 0.4, 0.9, 2 and IR bright galaxies).
