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Disentangling the ISM phases of the dwarf galaxy NGC 4214 using [C II] SOFIA/GREAT observations

Fahrion, K., Cormier, D., Bigiel, F., Hony, S., Abel, N. P., Cigan, Phillip, Csengeri, T., Graf, U. U., Lebouteiller, V., Madden, S. C., Wu, R. and Young, L. 2017. Disentangling the ISM phases of the dwarf galaxy NGC 4214 using [C II] SOFIA/GREAT observations. Astronomy & Astrophysics 599 , A9. 10.1051/0004-6361/201629341

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Abstract

Context. The [C ii] 158 μm fine structure line is one of the dominant cooling lines in the interstellar medium (ISM) and is an important tracer of star formation. Recent velocity-resolved studies with Herschel/HIFI and SOFIA/GREAT showed that the [C ii] line can constrain the properties of the ISM phases in star-forming regions. The [C ii] line as a tracer of star formation is particularly important in low-metallicity environments where CO emission is weak because of the presence of large amounts of CO-dark gas. Aims. The nearby irregular dwarf galaxy NGC 4214 offers an excellent opportunity to study an actively star-forming ISM at low metallicity. We analyzed the spectrally resolved [C ii] line profiles in three distinct regions at different evolutionary stages of NGC 4214 with respect to ancillary H i and CO data in order to study the origin of the [C ii] line. Methods. We used SOFIA/GREAT [C ii] 158 μm observations, H i data from THINGS, and CO(2 → 1) data from HERACLES to decompose the spectrally resolved [C ii] line profiles into components associated with neutral atomic and molecular gas. We use this decomposition to infer gas masses traced by [C ii] under different ISM conditions. Results. Averaged over all regions, we associate about 46% of the [C ii] emission with the H i emission. However, we can assign only ~9% of the total [C ii] emission to the cold neutral medium (CNM). We found that about 79% of the total molecular hydrogen mass is not traced by CO emission. Conclusions. On average, the fraction of CO-dark gas dominates the molecular gas mass budget. The fraction seems to depend on the evolutionary stage of the regions: it is highest in the region covering a super star cluster in NGC 4214, while it is lower in a more compact, more metal-rich region.

Item Type: Article
Date Type: Publication
Status: Published
Schools: Physics and Astronomy
Publisher: EDP Sciences
ISSN: 00046361
Date of First Compliant Deposit: 6 September 2017
Date of Acceptance: 2 November 2016
Last Modified: 07 Sep 2017 08:46
URI: http://orca.cf.ac.uk/id/eprint/104394

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