A panchromatic study of BLAST counterparts: Total star formation rate, morphology, active galactic nucleus fraction, and stellar mass

We carry out a multi-wavelength study of individual galaxies detected by the Balloon-borne Large Aperture Submillimeter Telescope (BLAST) and identified at other wavelengths, using data spanning the radio to the ultraviolet (UV). We develop a Monte Carlo method to account for flux boosting, source blending, and correlations among bands, which we use to derive deboosted far-infrared (FIR) luminosities for our sample. We estimate total star-formation rates (SFRs) for BLAST counterparts with z ≤ 0.9 by combining their FIR and UV luminosities. Star formation is heavily obscured at L_fir ≳ 10¹¹ L_⊙, z ≳ 0.5, but the contribution from unobscured starlight cannot be neglected at L_fir ≲ 10¹¹ L _̇, z ≲ 0.25. We assess that about 20% of the galaxies in our sample show indication of a type 1 active galactic nucleus, but their submillimeter emission is mainly due to star formation in the host galaxy. We compute stellar masses for a subset of 92 BLAST counterparts; these are relatively massive objects, with a median mass of ∼10¹¹ M _⊙, which seem to link the 24 μm and Submillimetre Common-User Bolometer Array (SCUBA) populations, in terms of both stellar mass and star formation activity. The bulk of the BLAST counterparts at z ≲ 1 appears to be run-of-the-mill star-forming galaxies, typically spiral in shape, with intermediate stellar masses and practically constant specific SFRs. On the other hand, the high-z tail of the BLAST counterparts significantly overlaps with the SCUBA population, in terms of both SFRs and stellar masses, with observed trends of specific SFR that support strong evolution and downsizing.