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 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).
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 language | English |
|---|---|
| Pages (from-to) | 2498-2513 |
| Journal | Monthly Notices of the Royal Astronomical Society |
| Volume | 449 |
| Issue number | 3 |
| Early online date | 2 Apr 2015 |
| DOIs | |
| Publication status | Published - 21 May 2015 |
Keywords
- ISM: evolution, ISM: lines and bands, galaxies: starburst, infrared: ISM
- RCUK
- STFC
- ST/I505905/1