Annu. Rev. Astron. Astrophys. 2000. 38: 667-715 Copyright © 2000 by Annual Reviews. All rights reserved

4.7. Sub-millimeter Sources

The commissioning of the sub-millimeter bolometer array camera SCUBA on the JCMT has opened a potentially revolutionary new window on the distant universe, permitting the detection of dust-reradiated energy from starburst galaxies and AGN out to almost arbitrarily large redshifts (thanks to the strongly negative k-correction at 850 µm, where SCUBA is most sensitive). A series of SCUBA surveys (e.g. [Smail et al. 1997, Barger et al. 1998] ) have now resolved a source population that comprises a substantial fraction of the far-IR background measured by COBE and that may account for a significant fraction of the global radiative energy density from galaxies. One of the first and deepest of such surveys was carried out by [Hughes et al. 1998], who observed the HDF for 50 hours, detecting five sources at 850 µm to a 4.4 limit of 2 mJy. Given the 15 SCUBA beam size and possible pointing uncertainties, the optical identifications for many (if not all) of these five sources remain in doubt, and some may be blends due to multiple objects. The brightest source, however, was subsequently pinpointed by a 1.3mm interferometric observation from institute de radioastronomie millimetrique (IRAM) ([Downes et al. 1999]). Unfortunately, this accurate position (which coincides with a microjansky radio source) did not fully settle the identification of the optical counterpart, falling halfway between two HDF galaxies separated by 2 (and almost certainly at very different redshifts). The second brightest SCUBA source, falling just outside the primary WFPC2 field, has no obvious counterpart in the flanking field WFPC2 images, nor in the NICMOS data of [Dickinson et al. 2000b].

Taking advantage of the frequent (but not universal) association of sub-millimeter sources with centimeter radio detections, [Barger et al. 1999] have used SCUBA to observe 14 radio sources in the HDF flanking fields with optical and near-IR counterparts fainter than I > 25 and K > 21, respectively. They surveyed roughly half of the flanking field area to a 3 depth of 6 mJy, detecting five of the "blank field" radio source targets in addition to two new radio-quiet sub-millimeter sources; however, none of the optical/near-IR bright sources were detected at 850 µm. For those sub-millimeter sources with radio counterparts, photometric redshifts from the 850 µm to 20 cm flux ratio [Carilli & Yun 1999, Barger et al. 1999, Cowie & Barger 1999], suggest that most lie in the redshift range 1 < z < 3. Sub-millimeter sources without radio counterparts may represent a higher redshift tail.

The HDF-N has also been imaged at 450 µm [Hughes et al. 1998] and 2.8mm [Wilner & Wright 1997]. No sources were detected at either wavelength, which is not surprising given the flux densities of the 850 µm detections.