2017A&A...603A..93M

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 have measured the molecular gas mass reservoir (M_H2) 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 M_H2 estimates within a factor of two or less, yielding gas depletion time-scales (τ_dep~=0.35Gyr) and gas-to-stellar mass ratios (M_H2/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.