Submillimeter Array identification of the millimeter-selected galaxy SSA22-AzTEC1: A protoquasar in a protocluster?

Abstract

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 S860 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 ≤1μm (J > 25.4 in AB, 2δ). 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 (AV ≈ 3.4 mag) of starlight from a stellar component with Mstar ∼ 1010.9M⊙, assuming z = 3.1. Additionally, we find a significant X-ray counterpart with a very hard spectrum (Γeff =0.34+0.57-0.61), strongly suggesting that SSA22-AzTEC1 harbors a luminous active galactic nuclei (AGNs; LX ≈ 3 × 1044 erg s-1) behind a large hydrogen column (NH ∼ 10 24 cm-2). 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. © 2010. The American Astronomical Society. All rights reserved. Printed in the U.S.A.