2010ApJ...724.1270T

We present results from Submillimeter Array (SMA) 860 µm subarcsecond 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 µm counterpart with a flux density of S_860 µm_= 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, whilst no object is found in Subaru optical and near-infrared deep images at wavelengths ≤1 µm (J > 25.4 in AB, 2σ). The photometric redshift estimate, using flux densities at ≥24 µm, 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_☉, assuming z = 3.1. Additionally, we find a significant X-ray counterpart with a very hard spectrum (Γ_eff= -0.34^+0.57_–0.61), strongly suggesting that SSA22-AzTEC1 harbors a luminous active galactic nuclei (AGNs; L_X~ 3x10⁴⁴ erg/s) behind a large hydrogen column (N_H∼ 10²⁴/cm2). The AGN, however, is responsible for only ∼10% of the bolometric 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.