THE INFRARED PROPERTIES OF SUBMILLIMETER GALAXIES: CLUES FROM ULTRADEEP 70 m IMAGING

We present 70 m properties of submillimeter galaxies (SMGs) in the Great Observatories Origins Deep Survey (GOODS) North field. Out of 30 submillimeter galaxies (S850 > 2 mJy) in the central GOODS-N region, we find two with secure 70 m detections. These are the first 70 m detections of SMGs. One of the matched SMGs is at z 0:5, and has S70 /S850 and S70 /S24 ratios consistent with a cool galaxy. The second SMG (z 1⁄4 1:2) has infrared-submillimeter colors that indicate it is more actively forming stars. We examine the average 70 m properties of the SMGs by performing a stacking analysis, which also allows us to estimate that S850 > 2 mJy SMGs contribute 9% 3% of the 70 m background light. The S850 /S70 colors of the SMG population as a whole is best fit by cool galaxies, and because of the redshifting effects these constraints are mainly on the lower z subsample. We fit spectral energy distributions (SEDs) to the far-infrared data points of the two detected SMGs and the average low-redshift SMG (zmedian 1⁄4 1:4). We find that the average low-z SMG has a cooler dust temperature than local ultraluminous infrared galaxies (ULIRGs) of similar luminosity and an SED that is best fit by scaled-up versions of normal spiral galaxies. The average low-z SMG is found to have a typical dust temperature T 1⁄4 21Y33K and infrared luminosity L8Y1000 m 1⁄4 8:0 ; 10 L . We estimate the AGN contribution to the total infrared luminosity of low-z SMGs is less than 23%. Subject headingg s: galaxies: evolution — galaxies: formation — galaxies: starburst — submillimeter