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Published November 2010 | Published
Journal Article Open

Measures of star formation rates from infrared (Herschel) and UV (GALEX) emissions of galaxies in the HerMES fields


The reliability of infrared (IR) and ultraviolet (UV) emissions to measure star formation rates (SFRs) in galaxies is investigated for a large sample of galaxies observed with the Spectral and Photometric Imaging Receiver (SPIRE) and the Photodetector Array Camera and Spectrometer (PACS) instruments on Herschel as part of the Herschel Multi-Tiered Extragalactic Survey (HerMES) project. We build flux-limited 250-μm samples of sources at redshift z < 1, cross-matched with the Spitzer/MIPS and GALEX catalogues. About 60 per cent of the Herschel sources are detected in UV. The total IR luminosities, L_(IR), of the sources are estimated using a spectral energy distribution (SED) fitting code that fits to fluxes between 24 and 500 μm. Dust attenuation is discussed on the basis of commonly used diagnostics: the L_(IR)/L_(UV) ratio and the slope, β, of the UV continuum. A mean dust attenuation A_(UV) of ≃ 3 mag is measured in the samples. L_(IR)/L_(UV) is found to correlate with L_(IR). Galaxies with L_(IR)  > 10^(11) L_⊙ and 0.5 < z < 1 exhibit a mean dust attenuation A_(UV) of about 0.7 mag lower than that found for their local counterparts, although with a large dispersion. Our galaxy samples span a large range of β and L_(IR)/L_(UV) values which, for the most part, are distributed between the ranges defined by the relations found locally for starburst and normal star-forming galaxies. As a consequence the recipe commonly applied to local starbursts is found to overestimate the dust attenuation correction in our galaxy sample by a factor of ~2–3. The SFRs deduced from L_(IR) are found to account for about 90 per cent of the total SFR; this percentage drops to 71 per cent for galaxies with SFR < 1 M_⊙ yr^(-1) (or L_(RI) < 10^(10) L_⊙). For these faint objects, one needs to combine UV and IR emissions to obtain an accurate measure of the SFR.

Additional Information

© 2010 The Authors. Journal compilation © 2010 RAS. Accepted 2010 July 6. Received 2010 July 6; in original form 2010 May 20. Article first published online: 19 Aug 2010. SPIRE has been developed by a consortium of institutes led by Cardiff University (UK) and including University of Lethbridge (Canada); NAOC (China); CEA, OAMP (France); IFSI, University of Padua (Italy); IAC (Spain); Stockholm Observatory (Sweden); Imperial College London, RAL, UCL-MSSL, UKATC, University of Sussex (UK) and Caltech/JPL, IPAC, 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). The data presented in this Letter will be released through the Herschel Database in Marseille HeDaM (http://hedam.oamp.fr/HerMES). This Letter makes use of TOPCAT, http://www.star.bristol.ac.uk/mbt/topcat/.

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