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A multiwavelength exploration of the [C II]/IR ratio in H-ATLAS/GAMA galaxies out to z = 0.2

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  • E. Ibar
  • M. A. Lara-Lopez
  • R. Herrera-Camus
  • R. Hopwood
  • A. Bauer
  • R. J. Ivison
  • M. J. Michalowski
  • H. Dannerbauer
  • P. van der Werf
  • D. Riechers
  • N. Bourne
  • M. Baes
  • I. Valtchanov
  • L. Dunne
  • A. Verma
  • S. Brough
  • A. Cooray
  • G. De Zotti
  • S. Dye
  • S. Eales
  • C. Furlanetto
  • S. Maddox
  • M. Smith
  • O. Steele
  • E. Valiante
We explore the behaviour of [C II] λ157.74 μm forbidden fine-structure line observed in a sample of 28 galaxies selected from ∼ 50 deg2 of the Herschel-Astrophysical Terahertz Large Area Survey survey. The sample is restricted to galaxies with flux densities higher than S160μm > 150 mJy and optical spectra from the Galaxy and Mass Assembly survey at 0.02 < z < 0.2. Far-IR spectra centred on this redshifted line were taken with the Photodetector Array Camera and Spectrometer instrument on-board the Herschel Space Observatory.
The galaxies span 10 < log(LIR/L) < 12 (where LIR ≡ LIR[8−1000 μm]) and
7.3 < log(L[C II]/L) < 9.3, covering a variety of optical galaxy morphologies. The sample exhibits the so-called [CII] deficit at high-IR luminosities, i.e. L[C II]/LIR (hereafter [CII]/IR) decreases at high LIR. We find significant differences between those galaxies presenting [C II]/IR >2.5×10−3 with respect to those showing lower ratios. In particular, those with high ratios tend to have: (1) LIR <1011 L; (2) cold dust temperatures, Td < 30 K; (3) disc-like morphologies in r-band images; (4) a Wide-field Infrared Survey Explorer colour 0.5 S12μm/S22μm 1.0; (5) low surface brightness ΣIR ≈ 108–9 L kpc−2, (6) and specific star formation rates of sSFR ≈0.05–3 Gyr−1. We suggest that the strength of the far-UV radiation fields (GO) is main parameter responsible for controlling the [C II]/IR ratio. It is possible that relatively high GO creates a positively charged dust grain distribution, impeding an efficient photoelectric extraction of electrons from these grains to then collisionally excite carbon atoms. Within the brighter IR population, 11 < log(L IR/L) < 12, the low [C II]/IR ratio is unlikely to be modified by [C II] self-absorption or controlled by the presence of a moderately luminous AGN (identified via the BPT diagram).
Original languageEnglish
Pages (from-to)2498-2513
JournalMonthly Notices of the Royal Astronomical Society
Issue number3
Early online date2 Apr 2015
Publication statusPublished - 21 May 2015


  • Ibar_etal_2015

    Rights statement: This article has been accepted for publication in Monthly Notices of the Royal Astronomical Society ©: 2015 The Authors. Published by Oxford University Press on behalf of the Royal Astronomical Society. All rights reserved

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