C+ Emission from the Magellanic Clouds II. [CII] maps of star-forming regions LMC-N 11, SMC-N 66, and several others

TL;DR

This study maps [CII] emission in star-forming regions of the Magellanic Clouds, revealing high [CII] line ratios due to low metallicity and dust, with implications for understanding heating processes in such environments.

Contribution

It provides detailed [CII] emission maps of specific star-forming regions in the Magellanic Clouds, highlighting the effects of metallicity and dust on line emission.

Findings

[CII]/CO and [CII]/FIR ratios are higher than in other galaxies.

Low metallicity environments have increased photoelectric heating efficiency.

[CII] strengths are slightly higher in the LMC than in the SMC.

Abstract

We study the 158 micron [CII] fine-structure line emission from star-forming regions as a function of metallicity. We have measured and mapped the [CII] emission from the very bright HII region complexes N 11 in the LMC and N 66 in the SMC, as well as the SMC HII regions N 25, N 27, N 83/N 84, and N 88, with the FIFI instrument on the Kuiper Airborne Observatory. In both the LMC and SMC, the ratio of the [CII] line to the CO line and to the far-infrared continuum emission is much higher than seen almost anywhere else, including Milky Way star-forming regions and whole galaxies. In the low metallicity, low dust-abundance environment of the LMC and the SMC, UV mean free path lengths are much greater than those in the higher-metallicity Milky Way. The increased photoelectric heating efficiencies cause significantly greater relative [CII] line emission strengths. At the same time, similar decreases in PAH abundances have the opposite effect, by diminishing photoelectric heating rates. Consequently, in low-metallicity environments the relative [CII] strengths are high but exhibit little further dependence on actual metallicity. Relative [CII] strengths are slightly higher in the LMC than in the SMC, which has both lower dust and lower PAH abundances.