Modelling [CI] emission from turbulent molecular clouds

Abstract

We use detailed numerical simulations of the coupled chemical, thermal and dynamical evolution of the gas in a turbulent molecular cloud to study the usefulness of the [CI] 609 micron and 370 micron fine structure emission lines as tracers of cloud structure. Emission from these lines is observed throughout molecular clouds, and yet the question of what we can learn from them about the physics of the clouds remains largely unexplored. We show that the fact that [CI] emission is widespread within molecular clouds is a simple consequence of the fact that the clouds are dominated by turbulent motions. Turbulence creates large density inhomogeneities, allowing radiation to penetrate deeply into the clouds. As a result, [CI] emitting gas is found throughout the cloud, rather than being concentrated at the edges. We examine how well we can use [CI] emission to trace the structure of the cloud, and show that the integrated intensity of the 609 micron line traces column density accurately over a wide range of visual extinctions. For extinctions greater than a few, [CI] and 13CO both perform well, but [CI] becomes a superior tracer of column densities for visual extinctions A_V <= 3 We have also studied the distribution of [CI] excitation temperatures in the gas, and show that these are typically smaller than the kinetic temperature, indicating that most of the carbon atoms are not in local thermodynamic equilibrium. We discuss how best to determine T_ex from observations of the [CI] lines, and how to use these values to estimate the column density of neutral atomic carbon. We show that even in the best case, we tend to systematically underestimate the atomic carbon content of the gas. Our results suggest that observationally-derived estimates of the atomic carbon content of real GMCs could be in error by as much as a factor of two.

23 pages, 22 figures. Updated treatment of 13CO plus other minor changes to match version accepted by MNRAS

References in corpus (26)

• The cosmological simulation code GADGET-2
• HEALPix -- a Framework for High Resolution Discretization, and Fast Analysis of Data Distributed on the Sphere
• An atomic and molecular database for analysis of submillimetre line observations
• The photodissociation and chemistry of CO isotopologues: applications to interstellar clouds and circumstellar disks
• Large-Scale Structure of the Molecular Gas in Taurus Revealed by High Linear Dynamic Range Spectral Line Mapping
• Simulating the formation of molecular clouds. I. Slow formation by gravitational collapse from static initial conditions
• CO Isotopologues in the Perseus Molecular Cloud Complex: the X-Factor and Regional Variations
• Simulating the formation of molecular clouds. II. Rapid formation from turbulent initial conditions
• The Effect of Line of Sight Temperature Variation and Noise on Dust Continuum Observations
• The CI lines as tracers of molecular gas, and their prospects at high redshifts
• Molecular Cloud Formation Behind Shock Waves
• The "True" Column Density Distribution in Star-Forming Molecular Clouds
• Modeling CO Emission: I. CO as a Column Density Tracer and the X-Factor in Molecular Clouds
• Modeling the Warm Ionized Interstellar Medium and Its Impact on Elemental Abundance Studies
• TreeCol: a novel approach to estimating column densities in astrophysical simulations
• Modeling CO Emission: II. The Physical Characteristics that Determine the X factor in Galactic Molecular Clouds
• How long does it take to form a molecular cloud?
• Star formation in metal-poor gas clouds
• Atomic Carbon in Galaxies
• Carbon Fractionation in PDRs
• An Alternative Accurate Tracer of Molecular Clouds: The "$X_{\mathrm{CI}}$-Factor"
• The ${}^{12}$CO/${}^{13}$CO ratio in turbulent molecular clouds
• On the temperature structure of the Galactic Centre cloud G0.253+0.016
• Emission of CO, CI, and CII in W3Main
• Clumpy photon-dominated regions in Carina. I. [CI] and mid-J CO lines in two 4'x4' fields
• Dust heating by the interstellar radiation field in models of turbulent molecular clouds

Cited by in corpus (67)

• Cool Outflows in Galaxies and their Implications
• Photodissociation and X-Ray Dominated Regions
• Cosmic-ray induced destruction of CO in star-forming galaxies
• Molecular gas in the Herschel-selected strongly lensed submillimeter galaxies at z~2-4 as probed by multi-J CO lines
• 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 $z=1-3$
• Circumnuclear Multi-phase Gas in the Circinus Galaxy II: The Molecular and Atomic Obscuring Structures Revealed with ALMA
• 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
• Turbulent Gas in Lensed Planck-selected Starbursts at redshifts 1-3.5
• The properties of the interstellar medium of galaxies across time as traced by the neutral atomic carbon [CI]
• SILCC-Zoom: H${}_2$ and CO-dark gas in molecular clouds -- The impact of feedback and magnetic fields
• 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
• Neutral carbon and CO in 76 (U)LIRGs and starburst galaxy centers A method to determine molecular gas properties in luminous galaxies
• Deceptively cold dust in the massive starburst galaxy GN20 at $z\sim 4$
• CO emission in distant galaxies on and above the main sequence
• Using CO line ratios to trace the physical properties of molecular clouds
• Histogram of oriented gradients: a technique for the study of molecular cloud formation
• Photodissociation Region Diagnostics Across Galactic Environments
• Tracing Molecular Gas in z $\simeq$ 6 Galaxies with [C$\mathrm{II}$]
• Probing Cosmic Reionization and Molecular Gas Growth with TIME
• CO excitation, molecular gas density and interstellar radiation field in local and high-redshift galaxies
• First Results from the $Herschel$ and ALMA Spectroscopic Surveys of the SMC: The Relationship Between [CII]-bright Gas and CO-bright Gas at Low Metallicity
• CO-dark gas and molecular filaments in Milky Way-type galaxies - II: The temperature distribution of the gas
• The Astrochemical Impact of Cosmic Rays in Protoclusters I: Molecular Cloud Chemistry
• Resolved neutral carbon emission in nearby galaxies: [CI] Lines as Total Molecular Gas Tracers
• How well does CO emission measure the H${}_2$ mass of MCs?
• ALMA Observations of Multiple-CO and C Lines Toward the Active Galactic Nucleus of NGC 7469: X-Ray-dominated Region Caught in the Act
• ALMA Finds Dew Drops in the Dusty Spider's Web
• Synthetic observations of star formation and the interstellar medium
• 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
• Molecular Line Observations in Two Dusty Star-Forming Galaxies at z = 6.9
• Atomic carbon as a powerful tracer of molecular gas in the high-redshift Universe: perspectives for ALMA
• The relationship between dust and [CI] at z=1 and beyond
• The subthermal excitation of the C{\sc i} lines in the molecular gas reservoirs of galaxies: its significance and potential utility
• Dynamical cloud formation traced by atomic and molecular gas
• 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
• Dense gas formation in the Musca filament due to the dissipation of a supersonic converging flow
• Bright Extragalactic ALMA Redshift Survey (BEARS) III: Detailed study of emission lines from 71 Herschel targets
• 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
• Extended Carbon Line Emission in the Galaxy: Searching for Dark Molecular Gas along the G328 Sightline
• Dark Molecular Gas in Simulations of z~0 Disc Galaxies
• Quenching by gas compression and consumption: A case study of a massive radio galaxy at z = 2.57
• The Carbon-to-H${}_2$, CO-to-H${}_2$ Conversion Factors and Carbon Abundance on Kiloparsec Scales in Nearby Galaxies
• ALMA and MUSE observations reveal a quiescent multi-phase circumgalactic medium around the z~3.6 radio galaxy 4C 19.71
• Transport of Protostellar Cosmic Rays in Turbulent Dense Cores
• The Baryonic Collapse Efficiency of Galaxy Groups in the RESOLVE and ECO Surveys
• The Astrochemical Impact of Cosmic Rays in Protoclusters II: CI-to-H${}_2$ and CO-to-H${}_2$ Conversion Factors
• CCAT-prime: Science with an Ultra-widefield Submillimeter Observatory at Cerro Chajnantor
• Big Three Dragons: Molecular Gas in a Bright Lyman-Break Galaxy at $z=7.15$
• The cold molecular gas in z$\gtrsim$6 quasar host galaxies
• Atacama Large Aperture Submillimeter Telescope (AtLAST) Science: Our Galaxy
• Observations of the [CI] (${}^3{P}_1$-${}^3{P}_0$) emission toward the massive star-forming region RCW38: further evidence for highly-clumped density distribution of the molecular gas
• Assessing the Impact of Astrochemistry on Molecular Cloud Turbulence Statistics
• Metallicity dependence of the CO-to-H${}_2$ and the [CI]-to-H${}_2$ conversion factors in galaxies
• CI and CO in Nearby Spiral Galaxies -- I. Line Ratio and Abundance Variations at ~ 200 pc Scales
• Atomic Carbon [CI]${(}^3{P}_1{-}^3{P}_0)$ Mapping of the Nearby Galaxy M83
• ATLASGAL-selected massive clumps in the inner Galaxy. X. Observations of atomic carbon at 492 GHz
• The G332 molecular cloud ring: I. Morphology and physical characteristics
• Extremely Low Molecular Gas Content in the Vicinity of a Red Nugget Galaxy at $z=1.91$
• Disentangling emission from star-forming regions in the Magellanic Clouds: Linking [OIII]88 micron and 24 micron
• The warm and dense Galaxy - tracing the formation of dense cloud structures out to the Galactic Center
• Deep kiloparsec view of the molecular gas in a massive star-forming galaxy at cosmic noon
• Extended atomic carbon around molecular clouds
• Cross-correlations between mm-wave line-intensity mapping and weak lensing surveys: preliminary consideration of long-term prospects
• First Submillimeter Lights from Dome A: Tracing the Carbon Cycle in the Feedback of Massive Stars