UNVEILING THE NATURE OF SUBMILLIMETER GALAXY SXDF 850.6

We present an 880 μm Submillimeter Array (SMA) detection of the submillimeter galaxy SXDF 850.6. SXDF 850.6 is a bright source (S850μm = 8 mJy) detected in the SCUBA Half Degree Extragalactic Survey and has multiple possible radio counterparts in its deep radio image obtained at the VLA. Our new SMA detection finds that the submillimeter emission coincides with the brightest radio emission that is found ∼8'' north of the coordinates determined from SCUBA. Despite the lack of detectable counterparts in deep UV/optical images, we find a source at the SMA position in near-infrared and longer wavelength images. We perform spectral energy distribution (SED) model fits to UV-optical-IR photometry (u, B, V, R, i', z', J, H, K, 3.6 μm, 4.5 μm, 5.8 μm, and 8.0 μm) and to submillimeter-radio photometry (850 μm, 880 μm, 1100 μm, and 21 cm) independently, and we find both are well described by starburst templates at a redshift of z ≅ 2.2 ± 0.3. The best-fit parameters from the UV-optical-IR SED fit are a redshift of z = 1.87+0.15-0.07, a stellar mass of M* = 2.5+2.2-0.3 x 1011 Msun, an extinction of AV = 3.0+0.3-1.0 mag, and an age of 720+1880-210 Myr. The submillimeter-radio SED fit provides a consistent redshift of z ∼ 1.8-2.5, an IR luminosity of LIR = (7-26) x1012 Lsun, and a star formation rate of 1300-4500 Msun yr-1. These results suggest that SXDF 850.6 is a mature system already having a massive amount of old stellar population constructed before its submillimeter bright phase and is experiencing a dusty starburst, possibly induced by major mergers.