The Canada-UK Deep Sub-Millimeter Survey II: First identifications, redshifts and implications for galaxy evolution

Identifications are sought for 12 sub-mm sources detected by Eales et al (1998). Six are securely identified, two have probable identifications and four remain unidentified with I_AB > 25. Spectroscopic and estimated photometric redshifts indicate that four of the sources have z < 1, and four have 1 < z < 3, with the remaining four empty field sources probably lying at z > 3. The spectral energy distributions of the identifications are consistent with those of high extinction starbursts such as Arp 220. The far-IR luminosities of the sources at z > 0.5 are of order 3 x 10^12 h_50^-2 L_sun, i.e. slightly larger than that of Arp 220. Based on this small sample, the cumulative bolometric luminosity function shows strong evolution to z ~ 1, but weaker or possibly even negative evolution beyond. The redshift dependence of the far-IR luminosity density does not appear, at this early stage, to be inconsistent with that seen in the ultraviolet luminosity density. Assuming that the energy source in the far-IR is massive stars, the total luminous output from star-formation in the Universe is probably dominated by the far-IR emission. The detected systems have individual star-formation rates (exceeding 300 h_50^-2 M_O yr^-1) that are much higher than seen in the ultraviolet selected samples, and which are sufficient to form substantial stellar populations on dynamical timescales of 10^8 yr. The association with merger-like morphologies and the obvious presence of dust makes it attractive to identify these systems as forming the metal-rich spheroid population, in which case we would infer that much of this activity has occurred relatively recently, at z ~ 2.