SUBMILLIMETER ARRAY IDENTIFICATION OF THE MILLIMETER-SELECTED GALAXY SSA22-AzTEC1: A PROTOQUASAR IN A PROTOCLUSTER?
We present results from Submillimeter Array (SMA) 860-micron sub-arcsec astrometry and multiwavelength observations of the brightest millimeter (S_1.1mm = 8.4 mJy) source, SSA22-AzTEC1, found near the core of the SSA22 protocluster that is traced by Lyα emitting galaxies at z = 3.09. We identify a 860-micron counterpart with a flux density of S_860um = 12.2 +/- 2.3 mJy and absolute positional accuracy that is better than 0.3". At the SMA position, we find radio to mid-infrared counterparts,
... d counterparts, whilst no object is found in Subaru optical and near-infrared deep images at wavelengths < 1 micron (J > 25.4 in AB, 2σ). The photometric redshift estimate, using flux densities at > 24 microns, indicates z_phot = 3.19^+0.26_-0.35, consistent with the protocluster redshift. We then model the near-to-mid-infrared spectral energy distribution (SED) of SSA22-AzTEC1, and find that the SED modeling requires a large extinction (A_V ≈ 3.4 mag) of starlight from a stellar component with M_star 10^10.9 M_sun, assuming z = 3.1. Additionally, we find a significant X-ray counterpart with a very hard spectrum (Gamma_eff = -0.34 ^+0.57_-0.61), strongly suggesting that SSA22-AzTEC1 harbors a luminous AGN (L_X 3*10^44 ergs s^-1) behind a large hydrogen column (N_H 10^24 cm^-2). The AGN, however, is responsible for only 10 luminosity of the host galaxy, and therefore the star-formation activity likely dominates the submillimeter emission. It is possible that SSA22-AzTEC1 is the first example of a protoquasar growing at the bottom of the gravitational potential underlying the SSA22 protocluster.