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

摘要

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 _(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 two or less, yielding gas depletion time-scales ( τ _(dep) ≈ 0.35 ?Gyr) and gas-to-stellar mass ratios ( M _(H_(2)) / 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.