SMAObservations of GOODS 850-11 and GOODS 850-13 - First Examples of
  Multiple Submillimeter Sources Resolved by an Interferometer
  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 ~1/3 of >5 mJy 850 um 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.
