Detection of an ultrabright submillimetre galaxy in the Subaru/XMM-NewtonDeep Fieldusing AzTEC/ASTE

Abstract

We report on the detection of an extremely bright (~37mJy at 1100μm and ~91mJy at 880μm) submillimetre galaxy (SMG), AzTEC-ASTE-SXDF1100.001 (hereafter referred to as SXDF1100.001 or Orochi), discovered in the 1100μm observations of the Subaru/XMM-NewtonDeep Fieldusing AzTEC on ASTE. Subsequent CARMA 1300-μm and SMA 880-μm observations successfully pinpoint the location of Orochi and suggest that it has two components, one extended [full width at half-maximum (FWHM) of ~4arcsec] and one compact (unresolved). Z-Spec on CSO has also been used to obtain a wide-band spectrum from 190 to 308GHz, although no significant emission/absorption lines were found. The derived upper limit to the line-to-continuum flux ratio is 0.1-0.3 (2σ) across the Z-Spec band. Based on the analysis of the derived spectral energy distribution from optical to radio wavelengths of possible counterparts near the SMA/CARMA peak position, we suggest that Orochi is a lensed, optically dark SMG lying atz~ 3.4 behind a foreground, optically visible (but red) galaxy atz~ 1.4. The deduced apparent (i.e., no correction for magnification) infrared luminosity (LIR) and star formation rate (SFR) are 6 × 1013L⊙ and 11000 M⊙yr-1, respectively, assuming that theLIR is dominated by star formation. These values suggest that Orochi will consume its gas reservoir within a short time-scale (3 × 107yr), which is indeed comparable to those in extreme starbursts like the centres of local ultraluminous infrared galaxies (ULIRGs). © 2011 The Authors Monthly Notices of the Royal Astronomical Society © 2011 RAS.