The effects of star formation on the low-metallicity ISM: NGC4214 mapped with Herschel/PACS spectroscopy

TL;DR

This study uses Herschel/PACS spectroscopy to map the low-metallicity dwarf galaxy NGC4214, revealing detailed FIR line emissions that highlight the impact of star formation on the interstellar medium's properties.

Contribution

It provides high-resolution FIR line maps of NGC4214, demonstrating the need for multiphase models to understand star formation effects in low-metallicity environments.

Findings

[O III] is the most luminous FIR line.

[C II]/CO ratios are significantly higher than in other galaxy types.

FIR lines account for up to 2% of the total infrared luminosity.

Abstract

We present Herschel/PACS spectroscopic maps of the dwarf galaxy NC4214 observed in 6 far infrared fine-structure lines: [C II] 158mu, [O III] 88mu, [O I] 63mu, [O I] 146mu, [N II] 122mu, and [N II] 205mu. The maps are sampled to the full telescope spatial resolution and reveal unprecedented detail on ~ 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 LTIR . 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.