The subthermal excitation of the C{\sc i} lines in the molecular gas reservoirs of galaxies: its significance and potential utility

Abstract

We examine a sample of 106 galaxies for which the total luminosities of the two fine structure lines ${}^3{P}_1$$\to$${}^3{P}_0$, and ${}^3{P}_2$$\to$${}^3{P}_1$ of neutral atomic carbon (C) are available, and find their average excitation conditions to be strongly subthermal. This is deduced from the CI(2-1)/(1-0) ratios ($R_{21/10}^{(ci)}$) modelled by the exact solutions of the corresponding 3-level system, without any special assumptions about the kinematic state of the concomitant ${\mathrm{H}}_2$ gas (and thus the corresponding line formation mechanism). This non-LTE excitation of the CI lines can induce the curious clustering of (CI,LTE)-derived gas temperatures near $\sim$25 K reported recently by Valentino et al. (2020), which is uncorellated to the actual gas temperatures. The non-LTE CI line excitation in the ISM of galaxies deprives us from a simple method for estimating molecular gas temperatures, and adds uncertainty in CI-based molecular gas mass estimates especially when the J=2-1 line is used. However the ${\mathrm{R}}_{21/10}^{(\mathrm{ci})}$=$\mathrm{F}(\mathrm{n},{\mathrm{T}}_{\mathrm{k}})$ ratio is now more valuable for joint CO/CI SLED and dust SED models of galaxies, and independent of the assumptions used in the CO radiative transfer models (e.g. the LVG approximation). Finally we speculate that the combination of low ratios ${\mathrm{R}}_{21/10}^{(\mathrm{ci})}\le 1$ and high ${\mathrm{T}}_{\mathrm{dust}}$ values found in some extreme starbursts indicates massive low-density molecular wind and/or circumgalactic gas reservoirs. If verified by imaging observations this can be a useful indicator of the presence of such reservoirs in~galaxies.

arXiv comment10 pages, 5 figures, accepted for publication in MNRAS

References in corpus (71)

• Star Formation in the Milky Way and Nearby Galaxies
• Cold Dark Clouds: The Initial Conditions for Star Formation
• Calibrating Extinction-Free Star Formation Rate Diagnostics with 33GHz Free-Free Emission in NGC6946
• Dust-Corrected Star Formation Rates of Galaxies. II. Combinations of Ultraviolet and Infrared Tracers
• HCN Survey of Normal Spiral, IR-luminous and Ultraluminous Galaxies
• Highly-excited CO emission in APM08279+5255 at z=3.9
• The CI lines as tracers of molecular gas, and their prospects at high redshifts
• Gas and Dust in the Cloverleaf Quasar at Redshift 2.5
• The Herschel Comprehensive (U)LIRG Emission Survey (HerCULES): CO Ladders, fine structure lines, and neutral gas cooling
• A Survey of Atomic Carbon at High Redshift
• Effective destruction of CO by cosmic rays: implications for tracing H${}_2$ gas in the Universe
• ALMA observations of atomic carbon in z~4 dusty star-forming galaxies
• Cosmic-ray induced destruction of CO in star-forming galaxies
• Extreme Cosmic-Ray-Dominated-Regions: a new paradigm for high star formation density events in the Universe
• DustPedia: Multiwavelength Photometry and Imagery of 875 Nearby Galaxies in 42 Ultraviolet--Microwave Bands
• A Survey of Atomic Carbon [C I] in High-redshift Main-Sequence Galaxies
• The ALMA Spectroscopic Survey in the HUDF: CO Excitation and Atomic Carbon in Star-Forming Galaxies at $z=1-3$
• ALMA Imaging of HCN, CS and dust in Arp 220 and NGC 6240
• Is atomic carbon a good tracer of molecular gas in metal-poor galaxies?
• Tracing the formation of molecular clouds via [CII], [CI] and CO emission
• Using [CI] to probe the Interstellar Medium in z~2.5 Sub-Millimeter Galaxies
• Turbulent Gas in Lensed Planck-selected Starbursts at redshifts 1-3.5
• A Herschel Space Observatory Spectral Line Survey of Local Luminous Infrared Galaxies from 194 to 671 Microns
• Modelling [CI] emission from turbulent molecular clouds
• Modeling Dust and Starlight in Galaxies Observed by Spitzer and Herschel: The KINGFISH Sample
• The properties of the interstellar medium of galaxies across time as traced by the neutral atomic carbon [CI]
• Molecular gas heating mechanisms, and star formation feedback in merger/s tarbursts: NGC 6240 and Arp 193 as case studies
• ALMA reveals starburst-like interstellar medium conditions in a compact star-forming galaxy at z ~ 2 using [CI] and CO
• CO Spectral Line Energy Distributions of IR-luminous galaxies and AGN
• An Alternative Accurate Tracer of Molecular Clouds: The "$X_{\mathrm{CI}}$-Factor"
• ALMA [CI]${}^3{P}_1{-}^3{P}_0$ observations of NGC6240: a puzzling molecular outflow, and the role of outflows in the global ${\alpha }_{\mathrm{CO}}$ factor of (U)LIRGs
• A Survey of the Molecular ISM Properties of Nearby Galaxies using the Herschel FTS
• Giant galaxy growing from recycled gas: ALMA maps the circumgalactic molecular medium of the Spiderweb in [CI]
• Neutral carbon and CO in 76 (U)LIRGs and starburst galaxy centers A method to determine molecular gas properties in luminous galaxies
• Planck's dusty GEMS. VI. Multi-J CO excitation and interstellar medium conditions in dusty starburst galaxies at z=2-4
• Deceptively cold dust in the massive starburst galaxy GN20 at $z\sim 4$
• CON-quest: Searching for the most obscured galaxy nuclei
• Neutral Carbon Emission in luminous infrared galaxies The \CI\ Lines as Total Molecular Gas Tracers
• AST/RO Observations of Atomic Carbon near the Galactic Center
• The Great Observatories All-Sky LIRG Survey: Herschel Image Atlas and Aperture Photometry
• Molecular gas in spiral galaxies: a new warm phase at large galactocentric distances?
• New places and phases of CO-poor/CI-rich molecular gas in the Universe
• Herschel/SPIRE Sub-millimeter Spectra of Local Active Galaxies
• Resolved neutral carbon emission in nearby galaxies: [CI] Lines as Total Molecular Gas Tracers
• ALMA Observations of Multiple-CO and C Lines Toward the Active Galactic Nucleus of NGC 7469: X-Ray-dominated Region Caught in the Act
• Planck's Dusty GEMS. VII. Atomic carbon and molecular gas in dusty starburst galaxies at z=2 to 4
• Atomic Carbon and CO Isotope Emission in the Vicinity of DR15
• Dust continuum, CO, and [C I] 1-0 lines: self-consistent H2 mass estimates and the possibility of globally CO-dark galaxies at $z=0.35$
• Herschel SPIRE-FTS Observations of Excited CO and [CI] in the Antennae (NGC 4038/39): Warm and Cold Molecular Gas
• SUPER. VI. A giant molecular halo around a z~2 quasar
• CO J=6--5 in Arp 220: strong effects of dust on high-J CO lines
• The Greenhouse Effect in Buried Galactic Nuclei and the Resonant HCN Vibrational Emission
• Neutral versus ionized gas kinematics at z~2.6: The AGN-host starburst galaxy PKS 0529-549
• High Atomic Carbon Abundance in Molecular Clouds in the Galactic Center Region
• Atomic Carbon Is a Temperature Probe in Dark Clouds
• Extreme conditions in the molecular gas of lensed star-forming galaxies at z~3
• [CI](1-0) and [CI](2-1) in resolved local galaxies
• ALMA Observations of Atomic Carbon [C I] (${{}^3\mathrm{P}}_1\to {{}^3\mathrm{P}}_0$) and Low-$J$ CO Lines in the Starburst Galaxy NGC 1808
• CO (7-6), [CI] 370 micron and [NII] 205 micron Line Emission of the QSO BRI 1335-0417 at Redshift 4.407
• Photon Dominated Region Modeling of Barnard 68
• Quenching by gas compression and consumption: A case study of a massive radio galaxy at z = 2.57
• SPIRE Spectroscopy of Early Type Galaxies
• The Interstellar Medium Properties of Heavily Reddened Quasars & Companions at z~2.5 with ALMA & JVLA
• The Carbon-to-H${}_2$, CO-to-H${}_2$ Conversion Factors and Carbon Abundance on Kiloparsec Scales in Nearby Galaxies
• ALMA [CI] observations toward the central region of a Seyfert galaxy NGC 613
• The nuclear and integrated far-infrared emission of nearby Seyfert galaxies
• Gas and dust in a z=2.8 obscured quasar
• Discovery of a [CI]-faint, CO-bright Galaxy: ALMA Observations of the Merging Galaxy NGC 6052
• VV 655 and NGC 4418: Implications of an interaction for the evolution of a LIRG
• Atomic Carbon [CI]${(}^3{P}_1{-}^3{P}_0)$ Mapping of the Nearby Galaxy M83
• ALMA view of the $\rho$ Ophiuchi A PDR with a 360-au beam: the [CI] emission originates from the plane-parallel PDR and extended gas

Cited by in corpus (18)

• Dust, CO and [CI]: Cross-calibration of molecular gas mass tracers in metal-rich galaxies across cosmic time
• A sensitive APEX and ALMA CO(1-0), CO(2-1), CO(3-2), and [CI](1-0) spectral survey of 40 local (U)LIRGs
• PDFchem: A new fast method to determine ISM properties and infer environmental parameters using probability distributions
• A cosmic stream of atomic carbon gas connected to a massive radio galaxy at redshift 3.8
• High resolution modeling of [CII], [CI], [OIII] and CO line emission from the ISM and CGM of a star forming galaxy at z ~ 6.5
• Observations of neutral carbon in 29 high-z lensed dusty star forming galaxies and the comparison of gas mass tracers
• SUNRISE: The rich molecular inventory of high-redshift dusty galaxies revealed by broadband spectral line surveys
• The cold interstellar medium of a normal sub-$L^{\star }$ galaxy at the end of reionization
• The cold molecular gas in z$\gtrsim$6 quasar host galaxies
• Infrared fine-structure lines at high redshift
• Molecular gas scaling relations for local star-forming galaxies in the low-$M_{\ast }$ regime
• Spatially-resolved relation between [CI] ${}^3{P}_1$-${}^3{P}_0$ and ${}^{12}$CO (1-0) in Arp 220
• Ionized Carbon in Galaxies: The [C II] 158 $\mu$m Line as a Total Molecular Gas Mass Tracer Revisited
• Evidence for environmental effects in the $z=4.3$ protocluster core SPT2349$-$56
• Molecular gas content and high excitation of a massive main-sequence galaxy at z = 3
• Extended atomic carbon around molecular clouds
• Tight correlation of star formation with [Ci] and CO lines across cosmic time
• Direct detection of cool molecular gas in a star-forming galaxy at $z=7.31$