LMC-N11 (LHA 120-N11) [CII], HI, CO spectra

DOI

The ambiguous origin of the [CII] 158um line in the interstellar medium complicates its use for diagnostics concerning the star-formation rate and physical conditions in photodissociation regions. We investigate the origin of [CII] in order to measure the total molecular gas content, the fraction of CO-dark H_2_ gas, and how these parameters are impacted by environmental effects such as stellar feedback. We observed the giant HII region N 11 in the Large Magellanic Cloud with SOFIA/GREAT. The [CII] line is resolved in velocity and compared to HI and CO, using a Bayesian approach to decompose the line profiles. A simple model accounting for collisions in the neutral atomic and molecular gas was used in order to derive the H_2_ column density traced by C^+^. The profile of [CII] most closely resembles that of CO, but the integrated [CII] line width lies between that of CO and that of HI. Using various methods, we find that [CII] mostly originates from the neutral gas. We show that [CII] mostly traces the CO-dark H_2_ gas but there is evidence of a weak contribution from neutral atomic gas preferentially in the faintest components (as opposed to components with low [CII]/CO or low CO column density). Most of the molecular gas is CO-dark. The CO-dark H_2_ gas, whose density is typically a few 100s/cm^3^ and thermal pressure in the range 10^3.5-5^K/cm^3^, is not always in pressure equilibrium with the neutral atomic gas. The fraction of CO-dark H_2_ gas decreases with increasing CO column density, with a slope that seems to depend on the impinging radiation field from nearby massive stars. Finally we extend previous measurements of the photoelectric-effect heating efficiency, which we find is constant across regions probed with Herschel, with [CII] and [OI] being the main coolants in faint and diffuse, and bright and compact regions, respectively, and with polycyclic aromatic hydrocarbon emission tracing the CO-dark H_2_ gas heating where [CII] and [OI] emit. We present an innovative spectral decomposition method that allows statistical trends to be derived for the molecular gas content using CO, [CII], and HI profiles. Our study highlights the importance of velocity-resolved photodissociation region (PDR) diagnostics and higher spatial resolution for HI observations as future steps.

Identifier
DOI http://doi.org/10.26093/cds/vizier.36320106
Source https://dc.g-vo.org/rr/q/lp/custom/CDS.VizieR/J/A+A/632/A106
Related Identifier https://cdsarc.cds.unistra.fr/viz-bin/cat/J/A+A/632/A106
Related Identifier http://vizier.cds.unistra.fr/viz-bin/VizieR-2?-source=J/A+A/632/A106
Metadata Access http://dc.g-vo.org/rr/q/pmh/pubreg.xml?verb=GetRecord&metadataPrefix=oai_b2find&identifier=ivo://CDS.VizieR/J/A+A/632/A106
Provenance
Creator Lebouteiller V.; Cormier D.; Madden S.C.; Galametz M.; Hony S.; Galliano F.,Chevance M.; Lee M.-Y.; Braine J.; Polles F.L.; Requena-Torres M.A.,Indebetouw R.; Hughes A.; Abel N.
Publisher CDS
Publication Year 2019
Rights https://cds.unistra.fr/vizier-org/licences_vizier.html
OpenAccess true
Contact CDS support team <cds-question(at)unistra.fr>
Representation
Resource Type Dataset; AstroObjects
Discipline Astrophysics and Astronomy; Galactic and extragalactic Astronomy; Interstellar medium; Natural Sciences; Physics