The applicability of far-infrared fine-structure lines as star formation rate tracers over wide ranges of metallicities and galaxy types^⋆

¹ Sterrenkundig Observatorium, Universiteit Gent, Krijgslaan 281 S9, 9000 Gent, Belgium
e-mail: Ilse.DeLooze@ugent.be
² Zentrum für Astronomie der Universität Heidelberg, Institut für Theoretische Astrophysik, Albert-Ueberle Str. 2, 69120 Heidelberg, Germany
³ Laboratoire AIM, CEA, Université Paris VII, IRFU/Service d′Astrophysique, Bat. 709, 91191 Gif-sur-Yvette, France
⁴ UK ALMA Regional Centre Node, Jodrell Bank Centre for Astrophysics, School of Physics and Astronomy, University of Manchester, Oxford Road, Manchester M13 9PL, UK
⁵ Institute of Astronomy, University of Cambridge, Madingley Road, Cambridge CB3 0HA, UK
⁶ Laboratoire d'Astrophysique de Marseille − LAM, Université Aix-Marseille & CNRS, UMR7326, 38 rue F. Joliot-Curie, 13388 Marseille CEDEX 13, France
⁷ Astrophysics Group, Imperial College, Blackett Laboratory, Prince Consort Road, London SW7 2AZ, UK
⁸ European Southern Observatory, Karl Schwarzschild Str. 2, 85748 Garching, Germany
⁹ Centre for Astrophysics and Supercomputing, Swinburne University of Technology, PO Box 218, Hawthorn VIC 3122, Australia
¹⁰ Department of Physics & Astronomy, University of California, Irvine CA 92697, USA
¹¹ Division of Physics, Astronomy and Mathematics, California Institute of Technology, Pasadena CA 91125, USA
¹² Max-Planck-Institute for Extraterrestrial Physics (MPE), Giessenbachstraße 1, 85748 Garching, Germany
¹³ ESA Research and Scientific Support Department, ESTEC/SRE-SA, Keplerlaan 1, 2201 AZ Noordwijk, The Netherlands
¹⁴ Department of Physics & Astronomy, University of Sussex, Brighton BN1 9QH, UK
¹⁵ Department of Physics & Astronomy, McMaster University, Hamilton, Ontario L8S 4M1, Canada
¹⁶ Department of Physics & Astronomy, University of Toledo, Toledo OH 43606, USA
¹⁷ Istituto di Astrofisica e Planetologia Spaziali, INAF-IAPS, Via Fosso del Cavaliere 100, 00133 Roma, Italy
¹⁸ School of Physics and Astronomy, Cardiff University, Queens Buildings, The Parade, Cardiff CF24 3AA, UK

Received: 14 August 2013
Accepted: 7 May 2014

Abstract

Aims. We analyze the applicability of far-infrared fine-structure lines [Cii] 158 μm, [Oi] 63 μm, and [Oiii] 88 μm to reliably trace the star formation rate (SFR) in a sample of low-metallicity dwarf galaxies from the Herschel Dwarf Galaxy Survey and, furthermore, extend the analysis to a broad sample of galaxies of various types and metallicities in the literature.

Methods. We study the trends and scatter in the relation between the SFR (as traced by GALEX FUV and MIPS 24 μm) and far-infrared line emission, on spatially resolved and global galaxy scales, in dwarf galaxies. We assemble far-infrared line measurements from the literature and infer whether the far-infrared lines can probe the SFR (as traced by the total infrared luminosity) in a variety of galaxy populations.

Results. In metal-poor dwarfs, the [Oi]₆₃ and [Oiii]₈₈ lines show the strongest correlation with the SFR with an uncertainty on the SFR estimates better than a factor of 2, while the link between [Cii] emission and the SFR is more dispersed (uncertainty factor of 2.6). The increased scatter in the SFR–L_[CII] relation toward low metal abundances, warm dust temperatures, and large filling factors of diffuse, highly ionized gas suggests that other cooling lines start to dominate depending on the density and ionization state of the gas. For the literature sample, we evaluate the correlations for a number of different galaxy populations. The [Cii] and [Oi]₆₃ lines are considered to be reliable SFR tracers in starburst galaxies, recovering the star formation activity within an uncertainty of factor 2. For sources with composite and active galactic nucleus (AGN) classifications, all three FIR lines can recover the SFR with an uncertainty factor of 2.3. The SFR calibrations for ultra-luminous infrared galaxies (ULIRGs) are similar to starbursts/AGNs in terms of scatter but offset from the starburst/AGN SFR relations because of line deficits relative to their total infrared luminosity. While the number of detections of the FIR fine-structure lines is still very limited at high redshift for [Oi]₆₃ and [Oiii]₈₈, we provide an SFR calibration for [Cii].