ALMA Deep Field in SSA22: Source Catalog and Number Counts

We present results from a deep 2'x3' (comoving scale of 3.7 Mpc x 5.5 Mpc at z=3) survey at 1.1 mm taken with the Atacama Large Millimeter/submillimeter Array (ALMA) in the SSA22 field. We observe the core region of a z = 3.09 protocluster, achieving a typical rms sensitivity of 60 micro-Jy/beam at a spatial resolution of 0".7. We detect 18 robust ALMA sources at a signal-to-noise ratio (SNR) > 5. Comparison between the ALMA map and a 1.1 mm map taken with the AzTEC camera on the Atacama Submillimeter Telescope Experiment (ASTE) indicates that three submillimeter sources discovered by the AzTEC/ASTE survey are resolved into eight individual submillimeter galaxies (SMGs) by ALMA. At least ten of our 18 ALMA SMGs have spectroscopic redshifts of z = 3.09, placing them in the protocluster. This shows that a number of dusty starburst galaxies are forming simultaneously in the core of the protocluster. The nine brightest ALMA SMGs with SNR > 10 have a median intrinsic angular size of 0".32+0".13-0".06 (2.4+1.0-0.4 physical kpc at z = 3.09), which is consistent with previous size measurements of SMGs in other fields. As expected the source counts show a possible excess compared to the counts in the general fields at S_1.1mm >= 1.0 mJy due to the protocluster. Our contiguous mm mapping highlights the importance of large-scale structures on the formation of dusty starburst galaxies.