Tracing the formation of molecular clouds via [CII], [CI] and CO emission

Abstract

Our understanding of how molecular clouds form in the interstellar medium (ISM) would be greatly helped if we had a reliable observational tracer of the gas flows responsible for forming the clouds. Fine structure emission from singly ionised and neutral carbon ([CII], [CI]) and rotational line emission from CO are all observed to be associated with molecular clouds. However, it remains unclear whether any of these tracers can be used to study the inflow of gas onto an assembling cloud, or whether they primarily trace the cloud once it has already assembled. In this paper, we address this issue with the help of high resolution simulations of molecular cloud formation that include a sophisticated treatment of the chemistry and thermal physics of the ISM. Our simulations demonstrate that both [CI] and CO emission trace gas that is predominantly molecular, with a density n ~ 500-1000 cm${}^{-3}$, much larger than the density of the inflowing gas. [CII] traces lower density material (n ~ 100 cm${}^{-3}$) that is mainly atomic at early times. A large fraction of the [CII] emission traces the same structures as the [CI] or CO emission, but some arises in the inflowing gas. Unfortunately, this emission is very faint and will be difficult to detect with current observational facilities, even for clouds situated in regions with an elevated interstellar radiation field.

arXiv comment17 pages, 9 figures. Version accepted by MNRAS

References in corpus (56)

• E pur si muove: Galiliean-invariant cosmological hydrodynamical simulations on a moving mesh
• An atomic and molecular database for analysis of submillimetre line observations
• The Neutral Atomic Phases of the ISM in the Galaxy
• The UMIST database for astrochemistry 2012
• Structure of Stationary Photodissociation Fronts
• The photodissociation and chemistry of CO isotopologues: applications to interstellar clouds and circumstellar disks
• Modelling Primordial Gas in Numerical Cosmology
• The SILCC (SImulating the LifeCycle of molecular Clouds) project: I. Chemical evolution of the supernova-driven ISM
• Physical Properties and Galactic Distribution of Molecular Clouds identified in the Galactic Ring Survey
• A Herschel [CII] Galactic plane survey I: the global distribution of ISM gas components
• Simulations of magnetic fields in isolated disk galaxies
• Turbulent Flow-Driven Molecular Cloud Formation: A Solution to the Post-T Tauri Problem?
• Simulating the formation of molecular clouds. I. Slow formation by gravitational collapse from static initial conditions
• Magnetohydrodynamics on an unstructured moving grid
• Simulating the formation of molecular clouds. II. Rapid formation from turbulent initial conditions
• The SILCC (SImulating the LifeCycle of molecular Clouds) project - II. Dynamical evolution of the supernova-driven ISM and the launching of outflows
• Molecular gas kinematics within the central 250 pc of the Milky Way
• Direct observation of a sharp transition to coherence in Dense Cores
• The Birth of Molecular Clouds: Formation of Atomic Precursors in Colliding Flows
• Molecular Cloud Formation Behind Shock Waves
• CO-dark gas and molecular filaments in Milky Way type galaxies
• Supernova Driving. I. The Origin of Molecular Cloud Turbulence
• 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
• Formation of Turbulent and Magnetized Molecular Clouds via Accretion Flows of HI Clouds
• Modeling CO Emission: II. The Physical Characteristics that Determine the X factor in Galactic Molecular Clouds
• Dynamics of Dense Cores in the Perseus Molecular Cloud
• Rapid Molecular Cloud and Star Formation: Mechanisms and Movies
• Effective destruction of CO by cosmic rays: implications for tracing H${}_2$ gas in the Universe
• Electron-Ion Recombination on Grains and Polycyclic Aromatic Hydrocarbons
• Isolating signatures of major cloud-cloud collisions using position-velocity diagrams
• SILCC-Zoom: The dynamical and chemical evolution of molecular clouds
• Two-Fluid MHD Simulations of Converging HI Flows in the Interstellar Medium. I: Methodology and Basic Results
• How long does it take to form a molecular cloud?
• Star formation in metal-poor gas clouds
• Cosmic-ray induced destruction of CO in star-forming galaxies
• The upGREAT 1.9 THz multi-pixel high resolution spectrometer for the SOFIA Observatory
• A Simple and Accurate Network for Hydrogen and Carbon Chemistry in the ISM
• Is atomic carbon a good tracer of molecular gas in metal-poor galaxies?
• Modelling [CI] emission from turbulent molecular clouds
• Gravitational contraction versus Supernova driving and the origin of the velocity dispersion-size relation in molecular clouds
• An Alternative Accurate Tracer of Molecular Clouds: The "$X_{\mathrm{CI}}$-Factor"
• The X_CO conversion factor from galactic multiphase ISM simulations
• Was a cloud-cloud collision the trigger of the recent star formation in Serpens?
• Using CO line ratios to trace the physical properties of molecular clouds
• GMC Collisions as Triggers of Star Formation. V. Observational Signatures
• The HI/OH/Recombination line survey of the inner Milky Way (THOR)
• Does the CO-to-H2 conversion factor depend on the star formation rate?
• CO-dark gas and molecular filaments in Milky Way-type galaxies - II: The temperature distribution of the gas
• Carbon in different phases ([CII], [CI], and CO) in infrared dark clouds: Cloud formation signatures and carbon gas fractions
• Synthetic [CII] emission maps of a simulated molecular cloud in formation
• On the resolution requirements for modelling molecular gas formation in solar neighbourhood conditions
• Non-Equilibrium Chemistry and Destruction of CO by X-ray Flares
• A Sample of [CII] Clouds Tracing Dense Clouds in Weak FUV Fields observed by Herschel
• Detection of a large fraction of atomic gas not associated with star-forming material in M17 SW

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• Photodissociation and X-Ray Dominated Regions
• The Cloud Factory I: Generating resolved filamentary molecular clouds from galactic-scale forces
• Simulations of the star-forming molecular gas in an interacting M51-like galaxy
• Dust, CO and [CI]: Cross-calibration of molecular gas mass tracers in metal-rich galaxies across cosmic time
• SILCC-Zoom: H${}_2$ and CO-dark gas in molecular clouds -- The impact of feedback and magnetic fields
• Photodissociation Region Diagnostics Across Galactic Environments
• On the origin of surprisingly cold gas discs in galaxies at high redshift
• Molecular gas in z~6 quasar host galaxies
• The Astrochemical Impact of Cosmic Rays in Protoclusters I: Molecular Cloud Chemistry
• The ALPINE-ALMA [CII] survey: Small Lya-[CII] velocity offsets in main-sequence galaxies at 4.4 < z < 6
• 3D chemical structure of diffuse turbulent ISM. I. Statistics of the HI-to-H${}_2$ transition
• Establishing the evolutionary timescales of the massive star formation process through chemistry
• Structure and kinematics of a massive galaxy at z ~ 7
• Ionized carbon as a tracer of the assembly of interstellar clouds
• Dynamical cloud formation traced by atomic and molecular gas
• Simulations of the star-forming molecular gas in an interacting M51-like galaxy: cloud population statistics
• The subthermal excitation of the C{\sc i} lines in the molecular gas reservoirs of galaxies: its significance and potential utility
• [CI](1-0) and [CI](2-1) in resolved local galaxies
• Galaxies with grains: unraveling dust evolution and extinction curves with hydrodynamical simulations
• Dense gas formation in the Musca filament due to the dissipation of a supersonic converging flow
• On the accuracy of HI observations in molecular clouds -- More cold HI than thought?
• Quantitative inference of the $H_2$ column densities from 3 mm molecular emission: A case study towards Orion B
• On the density regime probed by HCN emission
• Multi-scale decomposition of astronomical maps -- a constrained diffusion method
• An ACA Survey of [CI] ${}^3{P}_1{-}^3{P}_0$, CO $J=4-3$, and Dust Continuum in Nearby U/LIRG
• The Cloud Factory II: Gravoturbulent Kinematics of Resolved Molecular Clouds in a Galactic Potential
• The ALMA-CRISTAL survey: Resolved kinematic studies of main sequence star-forming galaxies at 4<z<6
• Magnetic fields do not suppress global star formation in low metallicity dwarf galaxies
• On the distribution of the Cold Neutral Medium in galaxy discs
• Fiery Cores: Bursty and Smooth Star Formation Distributions across Galaxy Centers in Cosmological Zoom-in Simulations
• The cold molecular gas in z$\gtrsim$6 quasar host galaxies
• Isotopic and vibrational-level dependence of H${}_2$ dissociation by electron impact
• Is the molecular KS relationship universal down to low metallicities?
• Towards the impact of GMC collisions on the star formation rate
• The SUPERCOLD-CGM survey: \\ I. Probing the extended CO(4-3) Emission of the Circumglactic medium in a sample of 10 Enormous Ly$\alpha$ Nebulae at $z\sim 2$
• Non-Equilibrium Abundances Treated Holistically (NEATH): the molecular composition of star-forming clouds
• Cloud properties across spatial scales in simulations of the interstellar medium
• Do simulated molecular clouds look like real ones?
• CI and CO in Nearby Spiral Galaxies -- I. Line Ratio and Abundance Variations at ~ 200 pc Scales
• The ALMA-CRISTAL survey: Extended [CII] emission in an interacting galaxy system at z ~ 5.5
• Searching for converging flows of atomic gas onto a molecular cloud
• Mapping gravity in stellar nurseries -- establishing the effectiveness of 2D acceleration maps
• Molecular Cloud Matching in CO and Dust in M33 I. High-Resolution Hydrogen Column Density Maps from Herschel
• The dynamical impact of cosmic rays in the Rhea magnetohydrodynamics simulations
• Chemical evolution during the formation of molecular clouds
• Filament Formation via Collision-induced Magnetic Reconnection -- Formation of a Star Cluster
• Density Exponent Analysis: Gravity-driven steepening of the density profiles of star-forming regions
• Decaying turbulence in molecular clouds: how does it affect filament networks and star formation?
• Shocks and Molecules in Diffuse Interstellar Cloud Pairs
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• The evolution of CH in Planck Galactic Cold Clumps
• The warm and dense Galaxy - tracing the formation of dense cloud structures out to the Galactic Center
• Line emission from filaments in molecular clouds
• Physical conditions in the gas phases of the giant HII region LMC-N11: II. Origin of [CII] and fraction of CO-dark gas
• The fragmentation of molecular clouds in starburst environments
• Molecular cloud matching in CO and dust in M33 II. Physical properties of giant molecular clouds
• Tight correlation of star formation with [Ci] and CO lines across cosmic time
• The ALPINE-CRISTAL-JWST Survey: Gas-phase abundance gradients of main sequence star-forming galaxies and their kinematics at $4<z<6$
• Insights into the structure and kinematics of a Milky Way-like galaxy
• Network of Star Formation: Fragmentation controlled by scale-dependent turbulent pressure and accretion onto the massive cores revealed in the Cygnus-X GMC complex
• Astro2020: The Cycling of Matter from the Interstellar Medium to Stars and back