J/A+A/632/A106 LMC-N11 (LHA 120-N11) [CII], HI, CO spectra (Lebouteiller+, 2019)
Physical conditions in the gas phases of the giant HII region LMC-N11:
II. Origin of [C II] and fraction of CO-dark.
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.
<Astron. Astrophys. 632, A106 (2019)>
=2019A&A...632A.106L 2019A&A...632A.106L (SIMBAD/NED BibCode)
ADC_Keywords: Magellanic Clouds ; H II regions ; Carbon monoxide ; H I data
Keywords: ISM: general - photon-dominated region - Magellanic Clouds -
submillimiter: ISM - infrared: ISM - galaxies: star formation
Abstract:
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 H2 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 H2 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 H2 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 H2 gas, whose density is typically a few
100s/cm3 and thermal pressure in the range 103.5-5K/cm3, is
not always in pressure equilibrium with the neutral atomic gas. The
fraction of CO-dark H2 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 H2 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.
Description:
Spectra of the 12 pointings in the paper in [CII] (SOFIA/GREAT),
HI (ATCA+Parkes), CO (MAGMA) and CO (ALMA; for pointings 2,3,4,5)
Objects:
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RA (2000) DE Designation(s)
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04 56 51.4 -66 24 24 LMC-N11 = LHA 120-N11
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File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
list.dat 74 40 List of spectra
sp/* . 40 Individual spectra
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See also:
J/A+A/418/841 : XMM-Newton observations of N11 in the LMC (Naze+, 2004)
J/AJ/132/2653 : JHKs photometry of N11 young stellar objects (Hatano+, 2006)
J/ApJS/213/23 : Giant HII region N11 in LMC deep Chandra obs. (Naze+, 2014)
J/A+A/628/A96 : 12CO J=3-2 datacube toward N11 (Celis Pena+, 2019)
Byte-by-byte Description of file: list.dat
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Bytes Format Units Label Explanations
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1- 26 A26 --- FileName Spectrum file name in subdirectory sp
31- 74 A44 --- Title Title of the spectrum
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Byte-by-byte Description of file: sp/*
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Bytes Format Units Label Explanations
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2- 7 F6.2 km/s HRV Heliocentric radial velocity
9- 18 E10.4 K T Main beam temperature
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Acknowledgements:
Vianney Lebouteiller, vianney.lebouteiller(at)cea.fr
(End) Vianney Lebouteiller [CDS], Patricia Vannier [CDS] 12-Nov-2019