SOFIA/FIFI-LS Full-disk [C ii] Mapping and CO-dark molecular gas across the nearby spiral galaxy NGC 6946
We present SOFIA/FIFI-LS observations of the [C ii] 158 μm cooling line across the nearby spiral galaxy NGC 6946. We combine these with UV, IR, CO, and H i data to compare [C ii] emission to dust properties, star formation rate (SFR), H2, and H i at 560 pc scales via stacking by environment (spiral...
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| Main Authors: | , |
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| Format: | Article (Journal) |
| Language: | English |
| Published: |
2020 October 29
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| In: |
The astrophysical journal
Year: 2020, Volume: 903, Issue: 1 |
| ISSN: | 1538-4357 |
| DOI: | 10.3847/1538-4357/abb677 |
| Online Access: | Verlag, lizenzpflichtig, Volltext: https://doi.org/10.3847/1538-4357/abb677
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| Author Notes: | F. Bigiel, I. de Looze, A. Krabbe, D. Cormier, A.T. Barnes, C. Fischer, A.D. Bolatto, A. Bryant, S. Colditz, N. Geis, R. Herrera-Camus, C. Iserlohe, R. Klein, A.K. Leroy, H. Linz, L.W. Looney, S.C. Madden, A. Poglitsch, J. Stutzki, and W.D. Vacca |
| Summary: | We present SOFIA/FIFI-LS observations of the [C ii] 158 μm cooling line across the nearby spiral galaxy NGC 6946. We combine these with UV, IR, CO, and H i data to compare [C ii] emission to dust properties, star formation rate (SFR), H2, and H i at 560 pc scales via stacking by environment (spiral arms, interarm, and center), radial profiles, and individual, beam-sized measurements. We attribute 73% of the [C ii] luminosity to arms, and 19% and 8% to the center and interarm region, respectively. [C ii]/TIR, [C ii]/CO, and [C ii]/PAH radial profiles are largely constant, but rise at large radii (≳ 8 kpc) and drop in the center (“[C ii] deficit”). This increase at large radii and the observed decline with the 70 μm/100 μm dust color are likely driven by radiation field hardness. We find a near proportional [C ii]-SFR scaling relation for beam-sized regions, though the exact scaling depends on methodology. [C ii] also becomes increasingly luminous relative to CO at low SFR (interarm or large radii), likely indicating more efficient photodissociation of CO and emphasizing the importance of [C ii] as an H2 and SFR tracer in such regimes. Finally, based on the observed [C ii] and CO radial profiles and different models, we find α CO to increase with radius, in line with the observed metallicity gradient. The low α CO (galaxy average ≲ 2 M ⊙ pc−2 (K km s−1)−1) and low [C ii]/CO ratios (∼400 on average) imply little CO-dark gas across NGC 6946, in contrast to estimates in the Milky Way. |
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| Item Description: | Gesehen am 03.12.2020 |
| Physical Description: | Online Resource |
| ISSN: | 1538-4357 |
| DOI: | 10.3847/1538-4357/abb677 |