Tracing H2 column density with atomic carbon (CI) and CO isotopologues

Abstract

We present first results of neutral carbon ([CI], 3P1 - 3P0 at 492 GHz) and carbon monoxide (13CO, J = 1 - 0) mapping in the Vela Molecular Ridge cloud C (VMR-C) and G333 giant molecular cloud complexes with the NANTEN2 and Mopra telescopes. For the four regions mapped in this work, we find that [CI] has very similar spectral emission profiles to 13CO, with comparable line widths. We find that [CI] has opacity of 0.1 - 1.3 across the mapped region while the [CI]/13CO peak brightness temperature ratio is between 0.2 to 0.8. The [CI] column density is an order of magnitude lower than that of 13CO. The H2 column density derived from [CI] is comparable to values obtained from 12CO. Our maps show CI is preferentially detected in gas with low temperatures (below 20 K), which possibly explains the comparable H2 column density calculated from both tracers (both CI and 12CO underestimate column density), as a significant amount of the CI in the warmer gas is likely in the higher energy state transition ([CI], 3P2 - 3P1 at 810 GHz), and thus it is likely that observations of both the above [CI] transitions are needed in order to recover the total H2 column density.

arXiv commentaccepted for publication in ApJ Letters

References in corpus (16)

• A computer program for fast non-LTE analysis of interstellar line spectra
• The ATLASGAL survey: a catalog of dust condensations in the Galactic plane
• Modeling CO Emission: I. CO as a Column Density Tracer and the X-Factor in Molecular Clouds
• BLAST: The Mass Function, Lifetimes, and Properties of Intermediate Mass Cores from a 50 Square Degree Submillimeter Galactic Survey in Vela (l = ~265)
• An Alternative Accurate Tracer of Molecular Clouds: The "$X_{\mathrm{CI}}$-Factor"
• The Giant Molecular Cloud associated with RCW 106 -- A 1.2 mm continuum mapping study
• Molecular line mapping of the giant molecular cloud associated with RCW 106 - III. Multi-molecular line mapping
• Molecular line mapping of the giant molecular cloud associated with RCW 106 - II. Column density and dynamical state of the clumps
• Extensive [CI] Mapping toward the Orion-A Molecular Cloud
• Atomic Carbon and CO Isotope Emission in the Vicinity of DR15
• A search for 22-GHz water masers within the giant molecular cloud associated with RCW106
• GEMINI near-infrared spectroscopic observations of young massive stars embedded in molecular clouds
• Detection of SiO emission from a massive dense cold core
• The Stellar Content of Obscured Galactic Giant HII Regions V: G333.1--0.4
• Radio and infrared recombination studies of the southern massive star-forming region G333.6-0.2
• The ionizing sources of luminous compact HII regions in the RCW106 and RCW122 clouds

Cited by in corpus (13)

• Cosmic-ray induced destruction of CO in star-forming galaxies
• New places and phases of CO-poor/CI-rich molecular gas in the Universe
• Photodissociation Region Diagnostics Across Galactic Environments
• RCW 36 in the Vela Molecular Ridge: Evidence for a high-mass star cluster formation triggered by Cloud-Cloud Collision
• Synthetic observations of star formation and the interstellar medium
• PDFchem: A new fast method to determine ISM properties and infer environmental parameters using probability distributions
• Extended Carbon Line Emission in the Galaxy: Searching for Dark Molecular Gas along the G328 Sightline
• The impact of cosmic-ray attenuation on the carbon cycle emission in molecular clouds
• The Astrochemical Impact of Cosmic Rays in Protoclusters II: CI-to-H${}_2$ and CO-to-H${}_2$ Conversion Factors
• SiO Outflows in the Most Luminous and Massive Protostellar Sources of the Southern Sky
• Metallicity dependence of the CO-to-H${}_2$ and the [CI]-to-H${}_2$ conversion factors in galaxies
• Ionized Carbon in Galaxies: The [C II] 158 $\mu$m Line as a Total Molecular Gas Mass Tracer Revisited
• Tight correlation of star formation with [Ci] and CO lines across cosmic time