2010A&A...518L..57C

We present Herschel/PACS spectroscopic maps of the dwarf galaxy NC4214 observed in 6 far infrared fine-structure lines: [CII] 158µm, [OIII] 88µm, [OI] 63µm, [OI] 146µm, [NII] 122µm, and [NII] 205µm. The maps are sampled to the full telescope spatial resolution and reveal unprecedented detail on ∼150pc size scales. We detect [CII] emission over the whole mapped area, [OIII] being the most luminous FIR line. The ratio of [OIII]/[CII] peaks at about 2 toward the sites of massive star formation, higher than ratios seen in dusty starburst galaxies. The [CII]/CO ratios are 20000 to 70000 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 L_TIR. 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.