Observations of a Z = 1.44 Dusty, Ultraluminous Galaxy and Implications for Deep Submillimeter Surveys

Abstract

We present new near-infrared and optical spectroscopic observations that confirm the redshift of the z=1.44 extremely red object ERO J164502+4626.4 (object 10 of Hu & Ridgway, formerly known as HR 10 or [HR94] 10) and a Hubble Space Telescope image that reveals a reflected S-shaped morphology at (rest-frame) near-ultraviolet wavelengths. The contrast between the rest-frame far-red (λλ8200-9800 Å) and near-UV (λλ2900-3900 Å) morphologies suggests that the central regions of the galaxy are heavily obscured by dust and that the galaxy is most likely an interacting or disturbed system. We also present new photometry of this object at 450, 850, and 1350 μm obtained using the Submillimeter Common-User Bolometer Array (SCUBA) submillimeter camera on the James Clerk Maxwell Telescope. Our submillimeter data are extremely sensitive to emission from cold dust at high redshift. The rest-frame spectral energy distribution of ERO J164502+4626.4 is best understood in terms of a highly reddened stellar population with ongoing star formation, as originally suggested by Graham & Dey. The new submillimeter data presented here indicate that the remarkable similarity to ultraluminous infrared galaxies (ULIRGs) such as Arp 220 and Mrk 231 extends into the rest-frame far-infrared, which bears the signature of thermal emission from dust, presumably heated by young stars. ERO J164502+4626.4 is extremely luminous (L~7×10¹² h^-2₅₀ L_solar) and dusty [M_dust~7×10⁸(T_dust/40 K)^-5 h^-2₅₀ M_solar]. If its luminosity is powered by young hot stars, then ERO J164502+4626.4 is forming stars at the prodigious rate of Ṁ=1000-2000 h^-2₅₀ M_solar yr^-1. We conclude that ERO J164502+4626.4 is a distant analog of the nearby ULIRG population, the more distant or less luminous counterparts of which may be missed by even the deepest existing optical surveys. The submillimeter emitters recently discovered by deep SCUBA surveys may be galaxies similar to ERO J164502+4626.4 (but perhaps more distant). This population of extremely dusty galaxies may also contribute significantly to the cosmic submillimeter background emission.

Based on observations obtained at Kitt Peak National Observatory, a division of the National Optical Astronomy Observatories, which is operated by the Association of Universities for Research in Astronomy, Inc., under cooperative agreement with the National Science Foundation.

Based on observations with the NASA/ESA Hubble Space Telescope obtained at the Space Science Institute, which is operated by the Association of Universities for Research Astronomy, Inc., under NASA contract NAS5-26555.