Thermal Emission from Dust in High-Z Galaxies

Abstract

A measure of the FIR luminosity in galaxies, assuming optically thin re-radiated emission from dust grains heated by young massive stars (and no contribution from an AGN), provides an estimate of their current starformation rates and dust masses. The fundamental reason for making millimetre and submillimetre continuum observations of high-z (z ~ 2 → 5) galaxies, which measure the rest-frame FIR emission, is to determine their evolutionary status. This is achieved in a relatively model-independent way by inferring the molecular gas mass, through a measure of dust mass and assuming a gas-to-dust ratio, available for further starformation and to compare this mass with the expected baryonic mass of a present-day counterpart. If this mass fraction is ≥ 0.9 then, together with the extreme FIR luminosities (L _FIR ≥ 10¹³ L _⊙) implying starformation rates ≥ 1000M _⊙ yr^-1, there is persuasive evidence that high-z galaxies are seen early in their evolution, whilst undergoing a significant (and possibly first) burst of massive starformation.