A Redshift Survey of the Submillimeter Galaxy Population

Abstract

We have obtained spectroscopic redshifts using the Keck-I telescope for a sample of 73 submillimeter (submm) galaxies for which precise positions are available. The galaxies lie at redshifts out to z=3.6, with a median redshift of 2.2. The dust-corrected ultraviolet (UV) luminosities of the galaxies rarely hint at their huge bolometric luminosities indicated by their radio/submm emission, underestimating the true luminosity by a median factor of ~100 for SMGs with pure starburst spectra. The 850mu, radio, and redshift data is used to estimate the dust temperatures (<Td>=36+-7 K), and characterize photometric redshifts. We calculate total infrared and bolometric luminosities, construct a luminosity function, and quantify the strong evolution of the submm population across z=0.5-3.5, relative to local IRAS galaxies. We conclude that bright submm galaxies contribute a comparable star formation density to Lyman-break galaxies at z=2-3 and including galaxies below our submm flux limit this population may be the dominant site of massive star formation at this epoch. The rapid evolution of submm galaxies and QSO populations contrasts with that seen in bolometrically lower luminosity galaxy samples selected in the restframe UV, and suggests a close link between submm galaxies and the formation and evolution of the galactic halos which host QSOs. [Abridged].Comment: 30 pages, 13 figures, accepted for April1 issue of ApJ (small typos and formatting fixed.

Dusty star-forming galaxies at high redshift

“…The median radio-identified SMG had a redshift of z ≈ 2.2 with far-infrared luminosities >10 12.5 L and star formation rates > 500 M yr −1 . By 2006, about 75 SMGs had confirmed spectroscopic redshifts (Swinbank et al, 2004;Chapman et al, 2005) and many were being followed up at other wavelengths to understand their comprehensive energy budget and evolutionary mechanisms. We describe the follow-up physical characterization of Scuba-selected SMGs more in § 5.…”

“…Although tens of optically-bright galaxies might be visible within one submillimeter beam, it is rare to have more than one radio-bright galaxy (here, radio-bright simply means radiodetected at S 1.4 > ∼ 50µJy). Once a radio position is in hand, the source can quickly be identified at other wavelengths and even followed-up using traditional spectroscopic methods in the optical and near-infrared (which was done most famously by Chapman et al, 2005, for a set of ∼75 Scuba-selected SMGs). With accurate positions and redshifts in hand, follow-up physical characterization can be done.…”

“…The initial assessment of the SMG redshift distribution came from Chapman et al (2005), now one of the most well known compilations of DSFGs in the literature. Chapman et al describe a population of 850µm-selected SMGs which have radio counterparts; these radio counterparts have astrometric precision <1 and provide excellent multi-slit spectroscopic targets.…”

“…For example, the DEIMOS spectrograph on Keck (Faber et al, 2003) has approximate maximum coverage 4500-9500Å in low resolution mode, which corresponds to a redshift desert of 1.6 < z < 3.2, making it not as ideal an instrument for follow-up of a population which peaks at z ∼ 2. Note that since the Chapman et al (2005) spectroscopic survey has been conducted, the red arm of the LRIS instrument has been upgraded so the coverage now runs ≈3000-10000Å, with only a small desert around z ≈1.7.…”

“…This was the procedure largely adopted for 850µm-selected SMGs (e.g. Smail et al, 2002;Blain et al, 2002;Chapman et al, 2004aChapman et al, , 2005 and lead to the first measurements of SMGs' dust temperatures. The dust temperatures implied from the FIR/radio correlation were, as expected (Eales et al, 2000;Blain et al, 2004a;Chapman et al, 2004a), statistically colder on average than local ULIRGs by ∼9 K, a difference which has been attributed to the dust temperature selection effect of 850µm samples (Casey et al, 2009a;Chapman et al, 2010;Magdis et al, 2010).…”