A multiwavelength exploration of the [C II]/IR ratio in H-ATLAS/GAMA galaxies out to z = 0.2
Abstract
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 S160 μm > 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 [C II] deficit at high-IR luminosities, i.e. L_[C II]/LIR (hereafter [C II]/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 ≲ S12 μm/S22 μm ≲ 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).
- Publication:
-
Monthly Notices of the Royal Astronomical Society
- Pub Date:
- May 2015
- DOI:
- 10.1093/mnras/stv439
- arXiv:
- arXiv:1503.01128
- Bibcode:
- 2015MNRAS.449.2498I
- Keywords:
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- ISM: evolution;
- ISM: lines and bands;
- galaxies: starburst;
- infrared: ISM;
- Astrophysics - Astrophysics of Galaxies;
- Astrophysics - Cosmology and Nongalactic Astrophysics
- E-Print:
- 16 pages, 10 figures, 3 tables