Dust and gas in star forming galaxies at z ~ 3 - extending galaxy uniformity

We present millimetre dust emission measurements of two Lyman Break Galaxies at z ∼ 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 measure 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 ∼2 or less, yielding gas depletion time-scales (τdep ≈ 0.35Gyrs) and gas-to-stellar mass ratios (MH2 /M∗ ≈ 0.5 − 1) for our z ∼ 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.