Journal
ASTROPHYSICAL JOURNAL LETTERS
Volume 726, Issue 2, Pages -Publisher
IOP PUBLISHING LTD
DOI: 10.1088/2041-8205/726/2/L18
Keywords
cosmology: observations; galaxies: evolution; galaxies: formation; galaxies: high-redshift; radio continuum: galaxies; submillimeter: galaxies
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Funding
- National Science Council of Taiwan [98-2112-M-001-003-MY2, 99-2112-M-001-012-MY3]
- NSF [AST 0709356, AST 0708793]
- Wisconsin Alumni Research Foundation
- David and Lucile Packard Foundation
- University of Wisconsin Research Committee
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We carried out extremely sensitive Submillimeter Array (SMA) 340 GHz continuum imaging on two submillimeter galaxies (SMGs): GOODS 850-11 and GOODS 850-13. The observations reach sub-mJy rms sensitivities and, interestingly, resolve both sources into multiple, physically unrelated SMGs. GOODS 850-11 is resolved into two sources at different redshifts. GOODS 850-13 is resolved into three sources, two with different spectroscopic redshifts and one only with a photometric redshift. All the SMA sources have fluxes in the 3-5 mJy range and all are detected at 1.4 GHz. Three of them are detected by Chandra, and one is a previously unknown X-ray SMG. This is the first time that single-dish SMGs are resolved into multiple unrelated sources and also the first time that the SMA has discovered new SMGs. Our results show that identifications of SMGs at any wavelengths other than the submillimeter itself can be misleading, since such identifications usually only pick up one of the real counterparts. Using simulations that mimic our SCUBA and SMA observations, we find that the number of triple systems detected in our SMA survey is much higher than that expected from the current best-determined number counts. We tentatively attribute this to clustering. We also predict that ALMA will find similar to 1/3 of > 5 mJy 850 mu m SCUBA sources to be multiple systems. Based on our SMA observations and simulations, we suggest that large samples of existing SMGs should be imaged with sensitive interferometric observations, even if the SMGs were previously thought to be securely identified.
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