ON THE NATURE OF THE FIRST GALAXIES SELECTED AT 350 Delta mm

• Published in: The Astrophysical journal 2009-11, Vol.706 (1), p.319-327
• Main Authors: Khan, Sophia A, Chanial, Pierre F, Willner, S P, Pearson, Chris P, Ashby, M L N, Benford, Dominic J, Clements, David L, Dye, Simon, Farrah, Duncan, Fazio, G G, Huang, J-S, Lebouteiller, V, Le Floc'h, Emeric, Mainetti, Gabriele, Moseley, S Harvey, Negrello, Mattia, Serjeant, Stephen, Shafer, Richard A, Staguhn, Johannes, Sumner, Timothy J, Vaccari, Mattia
• Format: Article
• Language: English
• ISSN: 0004-637X
• DOI: 10.1088/0004-637X/706/1/319

We present constraints on the nature of the first galaxies selected at 350 Delta *mm. The sample includes galaxies discovered in the deepest blank-field survey at 350 Delta *mm (in the Bootes Deep Field) and also later serendipitous detections in the Lockman Hole. In determining multiwavelength identifications, the 350 Delta *mm position and map resolution of the second generation Submillimeter High Angular Resolution Camera are critical, especially in the cases where multiple radio sources exist and the 24 Delta *mm counterparts are unresolved. Spectral energy distribution templates are fitted to identified counterparts, and the sample is found to comprise IR-luminous galaxies at 1 < z < 3 predominantly powered by star formation. The first spectrum of a 350 Delta *mm selected galaxy provides an additional confirmation, showing prominent dust grain features typically associated with star-forming galaxies. Compared to submillimeter galaxies selected at 850 and 1100 Delta *mm, galaxies selected at 350 Delta *mm have a similar range of far-infrared color temperatures. However, no 350 Delta *mm selected sources are reliably detected at 850 or 1100 Delta *mm. Galaxies in our sample with redshifts 1 < z < 2 show a tight correlation between the far- and mid-infrared flux densities, but galaxies at higher redshifts show a large dispersion in their mid- to far-infrared colors. This implies a limit to which the mid-IR emission traces the far-IR emission in star-forming galaxies. The 350 Delta *mm flux densities (15 < S 350 < 40 mJy) place these objects near the Herschel/SPIRE 350 Delta *mm confusion threshold, with the lower limit on the star formation rate density suggesting the bulk of the 350 Delta *mm contribution will come from less luminous infrared sources and normal galaxies. Therefore, the nature of the dominant source of the 350 Delta *mm background-star-forming galaxies in the epoch of peak star formation in the universe-could be more effectively probed using ground-based instruments with their angular resolution and sensitivity offering significant advantages over space-based imaging.