期刊
ASTRONOMY & ASTROPHYSICS
卷 518, 期 -, 页码 -出版社
EDP SCIENCES S A
DOI: 10.1051/0004-6361/201014699
关键词
galaxies: ISM; galaxies: individual: NGC 4214; ISM: line and bands; photon-dominated region (PDR); galaxies: dwarf
资金
- BMVIT (Austria)
- ESA-PRODEX (Belgium)
- CEA (France)
- DLR (Germany)
- ASI (Italy)
- CICYT (Spain)
- CNES (France)
- INAF (Italy)
- MCYT (Spain)
We present Herschel/PACS spectroscopic maps of the dwarf galaxy NC4214 observed in 6 far infrared fine-structure lines: [C II] 158 mu m, [O III] 88 mu m, [O I] 63 mu m, [O I] 146 mu m, [N II] 122 mu m, and [N II] 205 mu m. The maps are sampled to the full telescope spatial resolution and reveal unprecedented detail on similar to 150 pc size scales. We detect [C II] emission over the whole mapped area, [O III] being the most luminous FIR line. The ratio of [O III]/[C II] peaks at about 2 toward the sites of massive star formation, higher than ratios seen in dusty starburst galaxies. The [C II]/CO ratios are 20 000 to 70 000 toward the 2 massive clusters, which are at least an order of magnitude larger than spiral or dusty starbursts, and cannot be reconciled with single-slab PDR models. Toward the 2 massive star-forming regions, we find that L-[CII] is 0.5 to 0.8% of the L-TIR. All of the lines together contribute up to 2% of LTIR. These extreme findings are a consequence of the lower metallicity and young, massive-star formation commonly found in dwarf galaxies. These conditions promote large-scale photodissociation into the molecular reservoir, which is evident in the FIR line ratios. This illustrates the necessity to move to multiphase models applicable to star-forming clusters or galaxies as a whole.
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