The Astrophysical Journal, 691:1846–1853, 2009 February 1 doi:10.1088/0004-637X/691/2/1846 c  2009. The American Astronomical Society. All rights reserved. Printed in the U.S.A. SPITZER 70/160 μm OBSERVATIONS OF HIGH-REDSHIFT ULIRGs AND HyLIRGs IN THE BO ¨ OTES FIELD Krystal D. Tyler 1 , Emeric Le Floc’h 1 ,2,15 , George H. Rieke 1 , Arjun Dey 3 , Vandana Desai 4 , Kate Brand 5 ,16 , Colin Borys 6 , Buell T. Jannuzi 3 , Lee Armus 3 , Herve Dole 7 , Casey Papovich 1 ,8,15 , Michael J. I. Brown 9 , Myra Blaylock 1 , Sarah J. U. Higdon 10 , James L. Higdon 10 , Vassilis Charmandaris 11 ,12,13 , Matthew L. N. Ashby 14 , and Howard A. Smith 14 1 Steward Observatory, University of Arizona, 933 North Cherry Avenue, Tucson, AZ 85721, USA 2 Institute for Astronomy, University of Hawaii, 2680 Woodlawn Dr., Honolulu, HI 96822, USA 3 National Optical Astronomy Observatory, 950 North Cherry Avenue, Tucson, AZ 85726, USA 4 California Institute of Technology, Division of Physics, Mathematics, and Astronomy, MS 320-47, Pasadena, CA 91125, USA 5 Space Telescope Science Institute, 3700 San Martin Drive, Baltimore, MD 21218, USA 6 California Institute of Technology, 1200 E California Blvd., MS 100-22, Pasadena, CA 91125, USA 7 Institut d’Astrophysique Spatiale, Universit´ e Paris Sud, F-91405 Osay Cedex, France 8 Department of Physics, Texas A&M University, 4242 TAMU, College Station, TX 77843-4242, USA 9 School of Physics, Monash University, Clayton, Victoria 3800, Australia 10 Department of Physics, Georgia Southern University, P.O. Box 8031, Statesboro, GA 30460, USA 11 Department of Physics, University of Crete, GR-71003 Heraklion, Greece 12 IESL/Foundation for Research and Technology-Hellas, GR-71110, Heraklion, Greece 13 Chercheur Associ´ e, Observatoire de Paris, F-75014, Paris, France 14 Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138, USA Received 2007 September 4; accepted 2008 September 19; published 2009 February 12 ABSTRACT We present new 70 and 160 μm observations of a sample of extremely red (R − [24]  15 mag), mid- infrared bright, high-redshift (1.7  z  2.8) galaxies. All targets detected in the far-infrared exhibit ris- ing spectral energy distributions (SEDs) consistent with dust emission from obscured active galactic nuclei (AGNs) and/or star-forming regions in luminous IR galaxies (LIRGs). We find that the SEDs of the high- redshift sources are more similar to canonical AGN-dominated local ultraluminous IR galaxies (ULIRGs) with significant warm dust components than to typical local star-forming ULIRGs. The inferred IR (8–1000 μm) bolometric luminosities are found to be L bol ∼ 4 × 10 12 L ⊙ to ∼ 3 × 10 13 L ⊙ (ULIRGs/hyper- luminous IR galaxies (HyLIRGs)), representing the first robust constraints on L bol for this class of object. Key words: dust, extinction – galaxies: active – galaxies: high-redshift – galaxies: photometry – galaxies: starburst – infrared: galaxies Online-only material: color figures 1. INTRODUCTION The Spitzer Space Telescope (Werner et al. 2004) has revealed a large number of luminous, ultraluminous, and hyper-luminous infrared galaxies 17 (LIRGs, ULIRGs, and HyLIRGs) out to z ∼ 3. These objects have some of the highest IR luminosities known, sometimes exceeding 10 13 L ⊙ . Initially studied at mid- infrared (mid-IR) wavelengths from the ground by Rieke & Low (1972), this class of source has since been studied and cataloged using facilities such as IRAS, the Infrared Space Observatory (ISO), SCUBA, and Spitzer (Soifer et al. 1987; Smail et al. 1997; Blain et al. 1999; Elbaz et al. 1999; Dole et al. 2001; Farrah et al. 2003; Serjeant et al. 2004; Le Floc’h et al. 2005; Brand et al. 2007). While rare in the nearby universe, they contribute significantly to the cosmic infrared background (CIRB) and star formation density at high redshifts (Chary & Elbaz 2001; Franceschini et al. 2001; Blain et al. 2002; Lagache et al. 2003). To better understand galaxy evolution, especially the high- redshift stages, we need to better understand these IR-luminous sources. Despite their importance at high redshifts, the role of 15 Spitzer Fellow. 16 Giacconi Fellow. 17 LIRGs: 10 11 L ⊙  L IR  10 12 L ⊙ , ULIRGs: 10 12 L ⊙  L IR  10 13 L ⊙ , and HyLIRGs: L IR  10 13 L ⊙ , respectively, where L IR is determined from 8 to 1000 μm. IR-luminous galaxies in the evolution of stars and supermassive black holes in galaxies at z  1 has been poorly constrained so far due to the difficulty in identifying and characterizing them. The sensitivity of ISO has limited our view of these sources to z ∼ 1 (Flores et al. 1999; Aussel et al. 1999). Millimeter and submillimeter observations, such as those obtained with SCUBA and MAMBO, reach higher redshifts but are only sensitive to the extreme bright end of the luminosity function and are biased toward colder galaxies due to selection at 850 μm in the Rayleigh–Jeans regime (Chapman et al. 2003, 2005; Egami et al. 2004; Pope et al. 2006). With its superb sensitivity, Spitzer offers a new view into the properties of IR-luminous sources up to redshifts of z ∼ 3 and down to lower luminosities than previously reached. Many groups are exploring a variety of methods to identify active galactic nuclei (AGNs), particularly red ones, using the Spitzer data (e.g., Donley et al. 2005, 2007; Polletta et al. 2006; Lacy et al. 2004; Stern et al. 2005; Alonso-Herrero et al. 2006; Sajina et al. 2008). However, it must be noted that the Spitzer studies of high-redshift sources have so far mostly focused on their emission in the rest-frame mid-IR, where the instruments are most efficient. This can be problematic, since estimations of the bolometric luminosities of these sources rely on extrapolations of the spectral energy distributions (SEDs) to longer wavelengths. The extrapolations are quite uncertain for very luminous galaxies, for which the overall IR SED can 1846