z = 1 . 44 Dusty , Ultraluminous Galaxy and Implications for Deep Sub - mm

We present new near-infrared and optical spectroscopic observations which confirm the redshift of the z = 1.44 extremely red object ERO J164502+4626.4 (object # 10 of Hu & Ridgway 1994; formerly known as ‘HR 10’ or ‘[HR94] 10’) and a Hubble Space Telescope image which reveals a reflected-S–shaped morphology at (rest–frame) nearultraviolet wavelengths. The contrast between the rest–frame far-red (λλ8200−9800Å) and near-UV (λλ2900 − 3900Å) 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 450μm, 850μm and 1350μm obtained using the SCUBA submillimeter camera on the James Clerk Maxwell Telescope. Our sub-mm 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 (1996). 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 × 1012h 50 L⊙) and dusty (Mdust ≈ 7 × 10 (Tdust/40K) −5h 50 M⊙). 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 50 M⊙ yr −1. We conclude that ERO J164502+4626.4 is a distant analogue 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 sub-mm 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 sub-mm background emission. Subject headings: cosmology: observations — cosmology: early universe — galaxies: evolution — galaxies: formation — galaxies: starburst — galaxies: individual: ERO J164502+4646.4 (HR 10 or [HR94] 10)