Direct Measurement of the [C i] Luminosity to Molecular Gas Mass Conversion Factor in High-redshift Star-forming Galaxies

Heintz, K. E.; Watson, Derrick G.

doi:10.3847/2041-8213/ab6733

Cited by 38 publications

(48 citation statements)

References 50 publications

(54 reference statements)

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“…We find that the mean and standard deviation for X CI = (1.6 ± 0.3) × 10 −5 , which is similar to the values found in clouds in the Milky Way (Frerking et al 1989) and to the recent determination of X CI using GRB/QSO absorber systems using is a totally independent method (Heintz & Watson 2020). Several authors have adopted the use of an emprical quantity α C I , with similar units of M (K kms −1 ) −1 to that of α CO , which is used as standard in extragalactic studies.…”

Section: Calibration Factorssupporting

confidence: 86%

Dust continuum, CO, and [C i] 1 − 0 lines: self-consistent H2 mass estimates and the possibility of globally CO-‘dark’ galaxies at z = 0.35

Dunne

Maddox

Vlahakis

et al. 2020

Monthly Notices of the Royal Astronomical Society

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We present ALMA observations of a small but statistically complete sample of twelve 250μm selected galaxies at z = 0.35 designed to measure their dust submillimeter continuum emission as well as their $\rm {^{12}CO(1-0)}$ and atomic carbon [Ci](3P1-3P0) spectral lines. This is the first sample of galaxies with global measures of all three H2-mass tracers and which show star formation rates (4–26 $\rm M_{\odot }$ yr−1) and infra-red luminosities ($1-6\times 10^{11}\, {\,\rm L_{\odot }\,}$) typical of star forming galaxies in their era. We find a surprising diversity of morphology and kinematic structure; one-third of the sample have evidence for interaction with nearby smaller galaxies, several sources have disjoint dust and gas morphology. Moreover two galaxies have very high $L^{\prime }_{\rm CI}$ / $L^{\prime }_{\rm {CO}}$ ratios for their global molecular gas reservoirs; if confirmed, such extreme intensity ratios in a sample of dust selected, massive star forming galaxies presents a challenge to our understanding of ISM. Finally, we use the emission of the three molecular gas tracers, to determine the carbon abundance, $\rm {X_{CI}}$ , and CO–$\rm {H_2}$ conversion αCO in our sample, using a weak prior that the gas-to-dust ratio is similar to that of the Milky Way for these massive and metal rich galaxies. Using a likelihood method which simultaneously uses all three gas tracer measurements, we find mean values and errors on the mean of $\langle {\,\alpha _{\rm {CO}}\,}\rangle =3.0\pm 0.5\, \rm {{\,\rm M_{\odot }\,}\, (K\, kms^{-1}\, pc^2)^{-1}}$ and $\langle {\,\rm {X_{CI}}\,}\rangle =1.6\pm 0.1\times 10^{-5}$ (or ${\,\alpha _{\rm {CI}}\,}=18.8\, {\,\rm {M_{\odot }\, (K\, kms^{-1}\, pc^2)^{-1}}\,}$) and ${\,\delta _{\rm {GDR}}\,}=128\pm 16$ (or ${\,\alpha _{\rm {850}}\,}=5.9\times 10^{12}\, \rm {W\, Hz^{-1}\, {\,\rm M_{\odot }\,}^{-1}}$), where our starting assumption is that these metal rich galaxies have an average gas-to-dust ratio similar to that of the Milky Way centered on ${\,\delta _{\rm {GDR}}\,}=135$.

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Section: Calibration Factorssupporting

confidence: 86%

Dust continuum, CO, and [C i] 1 − 0 lines: self-consistent H2 mass estimates and the possibility of globally CO-‘dark’ galaxies at z = 0.35

Dunne

Maddox

Vlahakis

et al. 2020

Monthly Notices of the Royal Astronomical Society

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“…;Li et al 2018;Heintz & Watson 2020) deem [C i] to be a viable tracer of CO-dark H 2 . Likewise, ALMA has opened the window to numerous detections of [C ii]λ158 µm in the high-z universe, making [C ii]…”

mentioning

confidence: 99%

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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“…Once the atomic carbon mass has been computed (i.e., with Eq. (1) of Weiß et al 2005), we use the metallicity dependent prescription of Heintz & Watson (2020) for the carbon abundance to convert to molecular gas mass. Unlike method (ii) whose δ GDR (Z) scaling is calibrated on CO-derived gas masses, the Heintz & Watson (2020) relation was obtained directly from the [C i]/H 2 column density ratio observed in a sample of quasar and gamma ray burst absorbers at high-z, and hence is independent of the α CO factor.…”

Section: Molecular Gas Massmentioning

confidence: 99%

“…b Gas-to-dust mass ratio computed using the metallicity-dependent recipe from T18 as explained in Sect. 3.5. c Recipe from Heintz & Watson (2020), in units of M (K km s −1 pc 2 ) −1 . d Taken from Chisholm et al (2019).…”

Section: Appendix A: Stellar Z As a Proxy Of Gas-phase Metallicitymentioning

confidence: 99%

Molecular gas budget and characterization of intermediate-mass star-forming galaxies at z ≈ 2–3

Solimano

González-López²,

Barrientos³

et al. 2021

A&A

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Star-forming galaxies (SFGs) with stellar masses below 1010 M⊙ make up the bulk of the galaxy population at z > 2. The properties of the cold gas in these galaxies can only be probed in very deep observations or by targeting strongly lensed galaxies. Here we report the results of a pilot survey using the Atacama Compact Array of molecular gas in the most strongly magnified galaxies selected as giant arcs in optical data. The selection in rest-frame ultraviolet (UV) wavelengths ensures that sources are regular SFGs, without a priori indications of intense dusty starburst activity. We conducted Band 4 and Band 7 observations to detect mid-J CO, [C I] and thermal continuum as molecular gas tracers from four strongly lensed systems at z ≈ 2 − 3: our targets are SGAS J1226651.3+215220 (A and B), SGAS J003341.5+024217 and the Sunburst Arc. The measured molecular mass was then projected onto the source plane with detailed lens models developed from high resolution Hubble Space Telescope observations. Multiwavelength photometry was then used to obtain the intrinsic stellar mass and star formation rate via spectral energy distribution modeling. In only one of the sources are the three tracers robustly detected, while in the others they are either undetected or detected in continuum only. The implied molecular gass masses range from 4 × 109 M⊙ in the detected source to an upper limit of ≲109 M⊙ in the most magnified source. The inferred gas fraction and gas depletion timescale are found to lie approximately 0.5–1.0 dex below the established scaling relations based on previous studies of unlensed massive galaxies, but in relative agreement with existing literature about UV-bright lensed galaxies at these high redshifts. Our results indicate that the cold gas content of intermediate to low mass galaxies should not be extrapolated from the trends seen in more massive high-z galaxies. The apparent gas deficit is robust against biases in the stellar mass or star formation rate. However, we find that in this mass-metallicity range, the molecular gas mass measurements are severely limited by uncertainties in the current tracer-to-gas calibrations.

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Direct Measurement of the [C i] Luminosity to Molecular Gas Mass Conversion Factor in High-redshift Star-forming Galaxies

Cited by 38 publications

References 50 publications

Dust continuum, CO, and [C i] 1 − 0 lines: self-consistent H2 mass estimates and the possibility of globally CO-‘dark’ galaxies at z = 0.35

Dust continuum, CO, and [C i] 1 − 0 lines: self-consistent H2 mass estimates and the possibility of globally CO-‘dark’ galaxies at z = 0.35

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

Molecular gas budget and characterization of intermediate-mass star-forming galaxies at z ≈ 2–3

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