Using [C ii] 158 μm Emission from Isolated ISM Phases as a Star Formation Rate Indicator

Sutter, Jessica; Dale, Daniel A.; Croxall, K. V.; Pelligrini, Eric W.; Smith, John‐David T.; Appleton, P. N.; Beirão, P.; Bolatto, Alberto D.; Calzetti, Daniela; Crocker, Alison F.; Looze, I. De; Draine, B. T.; Galametz, M.; Groves, Brent; Hélou, G.; Herrera-Camus, Rodrigo; Hunt, L. K.; Kennicutt, Robert C.; Roussel, H.; Wolfire, M. G.

doi:10.3847/1538-4357/ab4da5

Cited by 33 publications

(57 citation statements)

References 103 publications

(128 reference statements)

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“…We derive a standard deviation about the fit of ∼0.25 dex, which is only slightly larger than that (∼0.21 dex) measured by Herrera-Camus et al (2015). Sutter et al (2019) fit measurements for 158 individual nuclear and extranuclear, kiloparsec-sized regions for 28 galaxies from the Herschel KINGFISH and Beyond the Peak (BtP) programs (Pellegrini et al 2013). They derive SFRs from a combination of FUV and 24 μm emission and apply a Bayesian linear regression technique to derive a power-law slope of 1.04±0.05 (solid gray line in Figure 5); we show their fit for all regions from the ionized and neutral medium.…”

Section: IIcontrasting

confidence: 53%

“…First, the carbon atom has a low ionization potential of 11.3 eV (lower than that of hydrogen or other metals like oxygen or nitrogen), so that singly ionized carbon exists in various phases of the ISM: neutral gas (the cold neutral medium, CNM, and photodissociation regions, PDRs), H II regions, and the warm ionized medium (WIM). While the phase breakdown has been, and continues to be, a topic of active investigation (e.g., Madden et al 1997;Cormier et al 2012Cormier et al , 2019De Looze et al 2014), recent, comprehensive observations in the Milky Way and nearby spiral galaxies, including NGC 6946, indicate that the neutral medium, and in particular the dense PDRs, is the dominant source of emission (Pineda et al 2013;Abdullah et al 2017;Croxall et al 2017;Sutter et al 2019).…”

Section: Introductionmentioning

confidence: 99%

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SOFIA/FIFI-LS Full-disk [C ii] Mapping and CO-dark Molecular Gas across the Nearby Spiral Galaxy NGC 6946

Bigiel

Krabbe

Cormier

et al. 2020

ApJ

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We present SOFIA/FIFI-LS observations of the [C II] 158 μm cooling line across the nearby spiral galaxy NGC 6946. We combine these with UV, IR, CO, and H I data to compare [C II] emission to dust properties, star formation rate (SFR), H 2 , and H I at 560 pc scales via stacking by environment (spiral arms, interarm, and center), radial profiles, and individual, beam-sized measurements. We attribute 73% of the [C II] luminosity to arms, and 19% and 8% to the center and interarm region, respectively. [C II]/TIR, [C II]/CO, and [C II]/PAH radial profiles are largely constant, but rise at large radii ( 8 kpc) and drop in the center ("[C II] deficit"). This increase at large radii and the observed decline with the 70 μm/100 μm dust color are likely driven by radiation field hardness. We find a near proportional [C II]-SFR scaling relation for beam-sized regions, though the exact scaling depends on methodology. [C II] also becomes increasingly luminous relative to CO at low SFR (interarm or large radii), likely indicating more efficient photodissociation of CO and emphasizing the importance of [C II] as an H 2 and SFR tracer in such regimes. Finally, based on the observed [C II] and CO radial profiles and different models, we find α CO to increase with radius, in line with the observed metallicity gradient. The low α CO (galaxy average  2 M e pc −2 (K km s −1) −1) and low [C II]/CO ratios (∼400 on average) imply little CO-dark gas across NGC 6946, in contrast to estimates in the Milky Way.

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Section: IIcontrasting

confidence: 53%

Section: Introductionmentioning

confidence: 99%

SOFIA/FIFI-LS Full-disk [C ii] Mapping and CO-dark Molecular Gas across the Nearby Spiral Galaxy NGC 6946

Bigiel

Krabbe

Cormier

et al. 2020

ApJ

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“…This requires observations of other ionised gas tracers, such as the commonly used FIR [N ii] lines, for example. Such studies often conclude that most of the [C ii] emission in galaxies arises from PDR regions, with a decreasing fraction of the total [C ii] emission arising from the ionised gas with decreasing metallicity (Kaufman et al 2006;Croxall et al 2017;Jameson et al 2018;Cormier et al 2019;Herrera-Camus et al 2016;Accurso et al 2017a;Sutter et al 2019). Also, in our study we have not taken into account any contributing molecular gas reservoirs originating in the WNM or CNM atomic phases.…”

Section: Possible Caveats and Limitationsmentioning

confidence: 93%

Tracing the total molecular gas in galaxies: [CII] and the CO-dark gas

Madden

Cormier

Hony

et al. 2020

A&A

126

128

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Context. Molecular gas is a necessary fuel for star formation. The CO (1−0) transition is often used to deduce the total molecular hydrogen but is challenging to detect in low-metallicity galaxies in spite of the star formation taking place. In contrast, the [C ii]λ158 µm is relatively bright, highlighting a potentially important reservoir of H 2 that is not traced by CO (1−0) but is residing in the C +-emitting regions. Aims. Here we aim to explore a method to quantify the total H 2 mass (M H 2) in galaxies and to decipher what parameters control the CO-dark reservoir. Methods. We present Cloudy grids of density, radiation field, and metallicity in terms of observed quantities, such as [O i], [C i], CO (1−0), [C ii], L TIR , and the total M H 2. We provide recipes based on these models to derive total M H 2 mass estimates from observations. We apply the models to the Herschel Dwarf Galaxy Survey, extracting the total M H 2 for each galaxy, and compare this to the H 2 determined from the observed CO (1−0) line. This allows us to quantify the reservoir of H 2 that is CO-dark and traced by the [C ii]λ158 µm. Results. We demonstrate that while the H 2 traced by CO (1−0) can be negligible, the [C ii]λ158 µm can trace the total H 2. We find 70 to 100% of the total H 2 mass is not traced by CO (1−0) in the dwarf galaxies, but is well-traced by [C ii]λ158 µm. The CO-dark gas mass fraction correlates with the observed L [C ii] /L CO(1−0) ratio. A conversion factor for [C ii]λ158 µm to total H 2 and a new CO-to-total-M H 2 conversion factor as a function of metallicity are presented. Conclusions. While low-metallicity galaxies may have a feeble molecular reservoir as surmised from CO observations, the presence of an important reservoir of molecular gas that is not detected by CO can exist. We suggest a general recipe to quantify the total mass of H 2 in galaxies, taking into account the CO and [C ii] observations. Accounting for this CO-dark H 2 gas, we find that the star-forming dwarf galaxies now fall on the Schmidt-Kennicutt relation. Their star-forming efficiency is rather normal because the reservoir from which they form stars is now more massive when introducing the [C ii] measures of the total H 2 compared to the small amount of H 2 in the CO-emitting region.

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“…With a critical density of n crit ∼ 3×10 3 −6×10 3 cm −3 at ∼ 100 K, [C II] is collisionally excited by H and H 2 in PDRs, as well as by warm electrons at 8,000 K (Goldsmith et al 2012). Ancillary observations of [N II] 205 µm emission constrain the fraction of [C II] emission originating from PDRs (e.g., Croxall et al 2012), which is greater for lower metallcities Cormier et al 2019), and approaches unity in warm and compact, dusty, star forming regions (Sutter et al 2019). Thus, [C II] can be used to trace PDR cooling in warm, compact environments, a critical physical process in atomic gas for star-formation to occur.…”

Section: Introductionmentioning

confidence: 99%

Measuring the Heating and Cooling of the Interstellar Medium at High Redshift: PAH and [C ii] Observations of the Same Star-forming Galaxies at z ∼ 2

McKinney

Pope

Armus

et al. 2020

ApJ

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Star formation depends critically on cooling mechanisms in the interstellar medium (ISM); however, thermal properties of gas in galaxies at the peak epoch of star formation (z ∼ 2) remain poorly understood. A limiting factor in understanding the multiphase ISM is the lack of multiple tracers detected in the same galaxies, such as Polycyclic Aromatic Hydrocarbon (PAH) emission, a tracer of a critical photoelectric heating mechanism in interstellar gas, and [C II] 158µm fine-structure emission, a principal coolant. We present ALMA Band 9 observations targeting [C II] in six z ∼ 2 star-forming galaxies with strong Spitzer IRS detections of PAH emission. All six galaxies are detected in dust continuum and marginally resolved. We compare the properties of PAH and [C II] emission, and constrain their relationship as a function of total infrared luminosity (L IR ) and IR surface density. [C II] emission is detected in one galaxy at high signal-to-noise (34σ), and we place a secure upper limit on a second source. The rest of our sample are not detected in [C II] likely due to redshift uncertainties and narrow ALMA bandpass windows. Our results are consistent with the deficit in [C II]/L IR and PAH/L IR observed in the literature. However, the ratio of [C II] to PAH emission at z ∼ 2 is possibly much lower than what is observed in nearby dusty star-forming galaxies. This could be the result of enhanced cooling via [O I] at high−z, hotter gas and dust temperatures, and/or a reduction in the photoelectric efficiency, in which the coupling between interstellar radiation and gas heating is diminished.

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Using [C ii] 158 μm Emission from Isolated ISM Phases as a Star Formation Rate Indicator

Cited by 33 publications

References 103 publications

SOFIA/FIFI-LS Full-disk [C ii] Mapping and CO-dark Molecular Gas across the Nearby Spiral Galaxy NGC 6946

SOFIA/FIFI-LS Full-disk [C ii] Mapping and CO-dark Molecular Gas across the Nearby Spiral Galaxy NGC 6946

Tracing the total molecular gas in galaxies: [CII] and the CO-dark gas

Measuring the Heating and Cooling of the Interstellar Medium at High Redshift: PAH and [C ii] Observations of the Same Star-forming Galaxies at z ∼ 2

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