First detection of [13CII] in the Large Magellanic Cloud

Abstract

[13CII] observations in several Galactic sources show that the fine-structure [12CII] emission is often optically thick (the optical depths around 1 to a few). The aim of our study is to test whether this also affects the [12CII] emission from nearby galaxies like the Large Magellanic Cloud (LMC). We observed three star-forming regions in the LMC with upGREAT on board SOFIA at the frequency of the [CII] line. The 4GHz band width covers all three hyperfine lines of [13CII] simultaneously. For the analysis, we combined the [13CII] F=1-0 and F=1-1 hyperfine components, as they do not overlap with the [12CII] line in velocity. Three positions in N159 and N160 show an enhancement of [13CII] compared to the abundance-ratio-scaled [12CII] profile. This is likely due to the [12CII] line being optically thick, supported by the fact that the [13CII] line profile is narrower than [12CII], the enhancement varies with velocity, and the peak velocity of [13CII] matches the [OI] 63um self-absorption. The [12CII] line profile is broader than expected from a simple optical depth broadening of the [13CII] line, supporting the scenario of several PDR components in one beam having varying [12CII] optical depths. The derived [12CII] optical depth at three positions (beam size of 14arcsec, corresponding to 3.4pc) is 1--3, which is similar to values observed in several Galactic sources shown in previous studies. If this also applies to distant galaxies, the [CII] intensity will be underestimated by a factor of approximately 2.

5 pages with 3 figures plus one page appendix with 4 figures, accepted for publication in A&A Letter

References in corpus (6)

• Early Science with SOFIA, the Stratospheric Observatory for Infrared Astronomy
• GREAT: the SOFIA high-frequency heterodyne instrument
• [CII] 158$\mu$m Emission and Metallicity in PDRs
• GREAT/SOFIA atmospheric calibration
• The upGREAT 1.9 THz multi-pixel high resolution spectrometer for the SOFIA Observatory
• Abundances and Isotope Ratios in the Magellanic Clouds: The Star Forming Environment of N113

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• The PDR structure and kinematics around the compact HII regions S235A and S235C with [CII], [13CII], [OI] and HCO+ line profiles
• The origin of the [CII]-deficit in a simulated dwarf galaxies starburst
• The KOSMA-$\tau$ PDR Model -- I. Recent updates to the numerical model of photo-dissociated regions
• Observation and calibration strategies for large-scale multi-beam velocity-resolved mapping of the [CII] emission in the Orion molecular cloud
• First detection of CF${}^{+}$ in the Large Magellanic Cloud
• LMC+: Large-scale mapping of [CII] and [OIII] in the LMC molecular ridge, I. Dataset and line ratio analyses
• Space as a spectroscopic laboratory: High-resolution spectroscopy of the [${}^{13}$C II] hyperfine structure with SOFIA/upGREAT