Carbon gas in SMC low-metallicity star-forming regions

Requeña-Torres, M. A.; Israel, F. P.; Okada, Yoko; Güsten, R.; Stutzki, J.; Risacher, C.; Simon, R.; Zinnecker, H.

doi:10.1051/0004-6361/201526244

Cited by 27 publications

(36 citation statements)

References 52 publications

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“…We find that ionized gas tends to contribute a small fraction of the [C ii] emission, with typical fractions around 19% in the LMC and 5% in the SMC. These contributions from ionized gas to the observed [C ii] emission are in agreement with those estimated using the unobscured [N ii] fine structure lines by Chevance et al (2016) and Okada et al (2015) in the 30 Dor and N159 regions in the LMC, respectively, and by Requena-Torres et al (2016) in several star forming regions in the SMC. The derived contributions from ionized gas to the observed [C ii] emission in the LMC and SMC are also consistent with those estimated in the Galactic plane (Pineda et al 2013).…”

Section: Ionized Gassupporting

confidence: 86%

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Characterizing the Transition from Diffuse Atomic to Dense Molecular Clouds in the Magellanic Clouds with [C ii], [C i], and CO

Pineda

Langer

Goldsmith

et al. 2017

ApJ

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We present and analyze deep Herschel/HIFI observations of the [C ii] 158 µm, [C i] 609 µm, and [C i] 370 µm lines towards 54 lines-of-sight (LOS) in the Large and Small Magellanic clouds. These observations are used to determine the physical conditions of the line-emitting gas, which we use to study the transition from atomic to molecular gas and from C + to C 0 to CO in their low metallicity environments. We trace gas with molecular fractions in the range 0.1 < f (H 2 ) < 1, between those in the diffuse H 2 gas detected by UV absorption (f (H 2 ) < 0.2) and well shielded regions in which hydrogen is essentially completely molecular. The C 0 and CO column densities are only measurable in regions with molecular fractions f (H 2 ) > 0.45 in both the LMC and SMC. Ionized carbon is the dominant gas-phase form of this element that is associated with molecular gas, with C 0 and CO representing a small fraction, implying that most (89% in the LMC and 77% in the SMC) of the molecular gas in our sample is CO-dark H 2 . The mean X CO conversion factors in our LMC and SMC sample are larger than the value typically found in the Milky Way. When applying a correction based on the filling factor of the CO emission, we find that the values of X CO in the LMC and SMC are closer to that in the Milky Way. The observed [C ii] intensity in our sample represents about 1% of the total far-infrared intensity from the LOSs observed in both Magellanic Clouds.

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Section: Ionized Gassupporting

confidence: 86%

“…The 30 Doradus region in the LMC has been studied in detail with the PACS instrument on Herschel (Chevance et al 2016). High velocity resolution [C ii] images of H ii regions in the LMC and SMC are starting to become available using SOFIA (Okada et al 2015;Requena-Torres et al 2016).…”

Section: Observations Of the Distribution Of [C Ii] [C I]mentioning

confidence: 99%

Characterizing the Transition from Diffuse Atomic to Dense Molecular Clouds in the Magellanic Clouds with [C ii], [C i], and CO

Pineda

Langer

Goldsmith

et al. 2017

ApJ

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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%

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

Lebouteiller

Cormier

Madden

et al. 2019

A&A

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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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“…These galaxies can have very weak CO emission (Schruba et al 2012;Cormier et al 2014). At the same time, dwarf galaxies can produce stars at rates that are normally found in starburst galaxies (e.g., Gallagher & Hunter 1984;Hunter et al 1989).…”

Section: Introductionmentioning

confidence: 96%

“…Nonetheless, the CO-to-H 2 conversion factor is a controversial quantity as it seems to vary with metallicity (Bolatto et al 2013;Poglitsch et al 1995;Cormier et al 2014;Narayanan et al 2011;Glover & Mac Low 2011). Furthermore, evidence for hidden molecular hydrogen ("CO-Dark Molecular Gas", Wolfire et al 2010) has been found not only in the Milky Way Planck Collaboration XIX 2011;Grenier et al 2005), but also in other galaxies (Israel 1997;Madden et al 1997;Requena-Torres et al 2016).…”

Section: Introductionmentioning

confidence: 99%

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

Fahrion

Cormier

Bigiel

et al. 2017

A&A

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Context. The [C ii] 158 µm fine structure line is one of the dominant cooling lines in the interstellar medium (ISM) and is an important tracer of star formation. Recent velocity-resolved studies with Herschel/HIFI and SOFIA/GREAT showed that the [C ii] line can constrain the properties of the ISM phases in star-forming regions. The [C ii] line as a tracer of star formation is particularly important in low-metallicity environments where CO emission is weak because of the presence of large amounts of CO-dark gas. Aims. The nearby irregular dwarf galaxy NGC 4214 offers an excellent opportunity to study an actively star-forming ISM at low metallicity. We analyzed the spectrally resolved [C ii] line profiles in three distinct regions at different evolutionary stages of NGC 4214 with respect to ancillary H i and CO data in order to study the origin of the [C ii] line. Methods. We used SOFIA/GREAT [C ii] 158 µm observations, H i data from THINGS, and CO(2 → 1) data from HERACLES to decompose the spectrally resolved [C ii] line profiles into components associated with neutral atomic and molecular gas. We use this decomposition to infer gas masses traced by [C ii] under different ISM conditions. Results. Averaged over all regions, we associate about 46% of the [C ii] emission with the H i emission. However, we can assign only ∼9% of the total [C ii] emission to the cold neutral medium (CNM). We found that about 79% of the total molecular hydrogen mass is not traced by CO emission. Conclusions. On average, the fraction of CO-dark gas dominates the molecular gas mass budget. The fraction seems to depend on the evolutionary stage of the regions: it is highest in the region covering a super star cluster in NGC 4214, while it is lower in a more compact, more metal-rich region.

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Carbon gas in SMC low-metallicity star-forming regions

Cited by 27 publications

References 52 publications

Characterizing the Transition from Diffuse Atomic to Dense Molecular Clouds in the Magellanic Clouds with [C ii], [C i], and CO

Characterizing the Transition from Diffuse Atomic to Dense Molecular Clouds in the Magellanic Clouds with [C ii], [C i], and CO

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

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

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Carbon gas in SMC low-metallicity star-forming regions

Cited by 27 publications

References 52 publications

Characterizing the Transition from Diffuse Atomic to Dense Molecular Clouds in the Magellanic Clouds with [C ii], [C i], and CO

Characterizing the Transition from Diffuse Atomic to Dense Molecular Clouds in the Magellanic Clouds with [C ii], [C i], and CO

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

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

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