We present millimetre dust emission measurements of two Lyman Break Galaxies at z \sim 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 \langle U \rangle with redshift , consistent with a rapidly decreasing gas metallicity in z > 2 galaxies .
Complementing our study with CO [ J=3 \rightarrow 2 ] emission line observations , we measure the molecular gas mass reservoir ( M _ { H _ { 2 } } ) 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 _ { H _ { 2 } } estimates within a factor of \sim 2 or less , yielding gas depletion time-scales ( \tau _ { dep } \approx 0.35 Gyrs ) and gas-to-stellar mass ratios ( M _ { H _ { 2 } } / M _ { \ast } \approx 0.5 - 1 ) for our z \sim 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 .