Dust and gas in star-forming galaxies at z ∼ 3 Extending galaxy uniformity to 11.5 billion years

We present millimetre dust emission measurements of two Lyman-break galaxies at z similar to 3 and construct for the first time fully sampled infrared spectral energy distributions (SEDs), from mid-IR to the Rayleigh-Jeans tail, of individually detected, unlensed, UV-selected, main sequence (MS) galaxies at z = 3. The SED modelling of the two sources confirms previous findings, based on stacked ensembles, of an increasing mean radiation field < U > with redshift, consistent with a rapidly decreasing gas metallicity in z > 2 galaxies. Complementing our study with CO[J = 3 -> 2] emission line observations, we have measured the molecular gas mass reservoir (MH2) of the systems using three independent approaches: 1) CO line observations; 2) the dust to gas mass ratio vs. metallicity relation; and 3) a single band, dust emission flux on the Rayleigh-Jeans side of the SED. All techniques return consistent MH2 estimates within a factor of two or less, yielding gas depletion time-scales (tau(dep) approximate to 0.35 Gyr) and gas-to-stellar mass ratios (M-H2/M-* approximate to 0 .5-1) for our z similar to 3 massive MS galaxies. The overall properties of our galaxies are consistent with trends and relations established at lower redshifts, extending the apparent uniformity of star-forming galaxies over the last 11.5 billion years.