350 μm Observations of Ultraluminous Infrared Galaxies at Intermediate Redshifts

Abstract

We present 350 m observations of 36 ultraluminous infrared galaxies (ULIRGs) at intermediate redshifts (0:089 z 0:926) using the Submillimeter High Angular Resolution Camera II (SHARC-II) on the Caltech Submillimeter Observatory (CSO). In total, 28 sources are detected at S/ N ! 3, providing the first flux measurements longward of 100 m for a statistically significant sample of ULIRGs in the redshift range 0:1 P z P 1:0. Combining our 350 m flux measurements with the existing IRAS 60 and 100 m data, we fit a single-temperature model to the spectral energy distribution (SED) and thereby estimate dust temperatures and far-IR luminosities. Assuming an emissivity index of ¼ 1:5, we find a median dust temperature and far-IR luminosity of T d ¼ 42:8 AE 7:1 K and log (L FIR /L) ¼ 12:2 AE 0:5, respectively. The far-IRYradio correlation observed in local star-forming galaxies is found to hold for ULIRGs in the redshift range 0:1 P z P 0:5, suggesting that the dust in these sources is predominantly heated by starbursts. We compare the far-IR luminosities and dust temperatures derived for dusty galaxy samples at low and high redshifts with our sample of ULIRGs at intermediate redshift. A general L FIR-T d relation is observed, albeit with significant scatter due to differing selection effects and variations in dust mass and grain properties. The relatively high dust temperatures observed for our sample compared to that of high-z submillimeter-selected starbursts with similar far-IR luminosities suggest that the dominant star formation in ULIRGs at moderate redshifts takes place on smaller spatial scales than is found at higher redshifts.