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

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. EalesC. Furlanetto, S. Maddox, M. Smith, O. Steele, D. Thomas, E. Valiante

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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


  • ISM: evolution, ISM: lines and bands, galaxies: starburst, infrared: ISM
  • RCUK
  • STFC
  • ST/I505905/1


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