C⁺ emission from the Magellanic Clouds

II. [C II] maps of star-forming regions LMC-N 11, SMC-N 66, and several others

¹ Sterrewacht Leiden, Leiden University, PO Box 9513, 2300 RA Leiden, The Netherlands
e-mail: israel@strw.leidenuniv.nl
² Center for Astrophysics and Space Astronomy, University of Colorado, Boulder, CO 80303, USA

Received: 15 December 2010
Accepted: 18 March 2011

Abstract

Context. We study the λ 158 μm [C II] fine-structure line emission from star-forming regions as a function of metallicity.

Aims. We have measured and mapped the [C II] emission from the very bright HII region complexes N 11 in the LMC and N 66 in the SMC; as well as the SMC H II regions N 25, N 27, N 83/N 84, and N 88 with the FIFI instrument on the Kuiper Airborne Observatory.

Methods. In both LMC and SMC, the ratio of [C II] line to 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.

Results. 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 [C II] 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 relative [C II] strengths are high but exhibit little further dependence on actual metallicity. Relative [C II] strengths are slightly higher in the LMC than in the SMC which has both lower dust and lower PAH abundances.