Disentangling the ISM phases of the dwarf galaxy NGC 4214 using [C ii] SOFIA/GREAT observations

Fahrion, Katja; Cormier, D.; Bigiel, Frank; Hony, S.; Abel, N. P.; Cigan, Phil; Csengeri, T.; Graf, U. U.; Lebouteiller, V.; Madden, S.; Wu, R.; Young, Lisa M.

doi:10.1051/0004-6361/201629341

Cited by 24 publications

(43 citation statements)

References 53 publications

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“…The H i profile is always much broader than the CO and [C ii] profiles, with FWHM in the range ≈ 16 − 40 km s −1 . Similar results were found in various star-forming regions within nearby galaxies (Braine et al 2012;de Blok et al 2016;Requena-Torres et al 2016;Okada et al 2015;Fahrion et al 2017) .…”

Section: Comparison Of the Spectral Profilessupporting

confidence: 84%

“…The fluxes measured with PACS and GREAT are shown in Table 3 for [C ii] and [N ii] 205 µm. The agreement is good overall for [C ii], although the PACS fluxes seem to be lower by a factor of 1.5 on average (see also Fahrion et al 2017 andSchneider et al 2018). A better agreement could be reached if the effective GREAT HPBW were somewhat larger (≈ 20 solid angle).…”

Section: Herschel/pacsmentioning

confidence: 78%

“…A better agreement could be reached if the effective GREAT HPBW were somewhat larger (≈ 20 solid angle). Furthermore, the PACS spectrometer data are calibrated for extended emission, so if the emission is indeed extended, the derived flux will scale with the aperture size; if the emission is point-like however, the total flux of the point source is enclosed in an area somewhat larger than the FWHM of the instrument, and the enclosed energy could be typically underestimated by 10 − 15% 3 (see also Fahrion et al 2017).…”

Section: Herschel/pacsmentioning

confidence: 99%

“…Our results are also in general agreement with other studies in nearby low-metallicity environments. Fahrion et al (2017) used SOFIA/GREAT observations the dwarf galaxy NGC 4214 at ≈ 200 pc spatial scale and found that only ≈ 10% of [C ii] could be attributed to the CNM and that ≈ 80% of the H 2 mass is not traced by CO. Other studies in the Magellanic Clouds also show significant CO-dark H 2 gas fractions. Requena-Torres et al (2016) examined several star-forming regions in the SMC, and found that most of the [C ii] emission originates from COdark H 2 gas.…”

Section: Fraction Of Co-dark H 2 Gasmentioning

confidence: 99%

“…Metallicity effects and massive stellar feedback effects are conveniently probed through observations of nearby starforming dwarf galaxies. Fahrion et al (2017) examined the ISM at ≈ 200 pc scales in the nearby star-forming galaxy NGC 4214 and found that about half of the [C ii] traces the atomic gas and that most (≈ 80%) of the H 2 gas is CO-dark. The authors also found that f dark is higher in the low-metallicity diffuse region where a super stellar cluster is located, although the relative influence of metallicity and feedback remains uncertain.…”

Section: Introductionmentioning

confidence: 99%

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Physical conditions in the gas phases of the giant H II region LMC-N 11

Lebouteiller

Cormier

Madden

et al. 2019

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Context. The ambiguous origin of the [C ii] 158 µm line in the interstellar medium complicates its use for diagnostics concerning the star-formation rate and physical conditions in photodissociation regions. Aims. We investigate the origin of [C ii] 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. Methods. We observed the giant H ii region N 11 in the Large Magellanic Cloud with SOFIA/GREAT. The [C ii] line is resolved in velocity and compared to H i 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 + .Results. The profile of [C ii] most closely resembles that of CO, but the integrated [C ii] line width lies between that of CO and that of H i. Using various methods, we find that [C ii] mostly originates from the neutral gas. We show that [C ii] 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 [C ii]/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 [C ii] and [O i] 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 [C ii] and [O i] emit. Conclusions. We present an innovative spectral decomposition method that allows statistical trends to be derived for the molecular gas content using CO, [C ii], and H i profiles. Our study highlights the importance of velocity-resolved photodissociation region (PDR) diagnostics and higher spatial resolution for H i observations as future steps.

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