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Published November 2010 | Published + Supplemental Material
Journal Article Open

Herschel-SPIRE, far-infrared properties of millimetre-bright and -faint radio galaxies


We present the first study of the far-infrared (FIR) properties of high-redshift, radio-selected ultraluminous infrared galaxies (ULIRGs) using deep observations obtained with the Spectral and Photometric Imaging Receiver (SPIRE) from the Herschel Multi-tiered Extragalactic Survey (HerMES). These galaxies span a large range of 850-μm fluxes from submillimetre-luminous ∼10 mJy sources (SCUBA galaxies) to ∼1.5 mJy from stacked SCUBA non-detections, thus likely representing a complete distribution of ULIRG spectral energy distributions (SEDs). From Keck spectroscopic surveys in the Lockman-North field we identified a sample of 31 submillimetre galaxies (SMGs) and 37 submillimetre-faint, optically faint radio galaxies (OFRGs), all with radio-inferred IR luminosities >10^(12) L_⊙. These galaxies were cross-identified with SPIRE 250-, 350- and 500-μm catalogues based on fluxes extracted at 24-μm positions in the SWIRE survey, yielding a sample of more than half of the galaxies well detected in at least two of the SPIRE bandpasses. By fitting greybody dust models to the SPIRE photometry together with SCUBA 850-μm measurements (for OFRGs, only 850-inline image upper limits), we infer dust temperatures and FIR luminosities. The OFRGs detected by SPIRE have median 〈T_d〉= 41 ± 5 K and the SMGs have 〈T_d〉= 34 ± 5 K, both in reasonable agreement with previous (pre-Herschel) estimates, reaffirming that the local FIR/radio correlation holds (at least for this subset of high-z ULIRGs) at high redshift (we measure 〈q_(IR)〉= 2.43 ± 0.21 using S_(IR) derived from greybody fit coupled with a power-law extrapolation to the 24 μm). Our observations first confirm that a substantial fraction of OFRGs exhibits large infrared luminosities corresponding to SFRs of ∼400 M_⊙ yr^−1. The SPIRE observations secondly confirm the higher dust temperatures for these OFRGs than similarly selected SMGs, consistent with early predictions of the submillimetre-faint radio populations. Our observations also clearly confirm the large infrared luminosities of most SMGs selected with S_(850 μm) > 5 mJy and radio and strong 24-μm detections, corresponding to SFRs of ∼700 M_⊙ yr^(−1).

Additional Information

© 2010 The Authors. Journal compilation © 2010 RAS. Accepted 2010 September 14. Received 2010 September 11; in original form 2010 July 20. Article first published online: 2 Nov 2010. The data presented in this Letter will be released through the Herschel data base in Marseille HeDaM (hedam.oamp.fr/HerMES). SPIRE has been developed by a consortium of institutes led by Cardiff University (UK) and including University of Lethbridge (Canada), NAOC (China), CEA, LAM (France), IFSI, University of Padua (Italy), IAC (Spain), Stockholm Observatory (Sweden), Imperial College London, RAL, UCL-MSSL, UKATC, University of Sussex (UK), Caltech, JPL, NHSC, University of Colorado (USA). This development has been supported by national funding agencies: CSA (Canada); NAOC (China); CEA, CNES, CNRS (France); ASI (Italy); MCINN (Spain); SNSB (Sweden); STFC (UK) and NASA (USA). Data presented herein were obtained using the W. M. Keck Observatory, which is operated as a scientific partnership among Caltech, the University of California and NASA. The Observatory was made possible by the generous financial support of the W. M. Keck Foundation.

Attached Files

Published - Chapman2010p13721Mon_Not_R_Astron_Soc.pdf

Supplemental Material - MNL2_956_sm_TableS1.doc


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