Probing the Cold Deep Depths of the California Molecular Cloud: The Icy Relationship between CO and Dust

Abstract

We study the relationship between molecular gas and dust in the California Molecular Cloud over an unprecedented dynamic range of cloud depth (Av = 3 - 60 magnitudes). We compare deep Herschel-based measurements of dust extinction with observations of the 12CO, 13CO, and C18O J=2-1 lines on sub-parsec scales across the cloud. We directly measure the ratio of CO integrated intensity to dust extinction to derive the CO X-factor at over 1e5 independent locations in the cloud. Confirming an earlier study, we find that no single 12CO X-factor can characterize the molecular gas in the cold ( Tdust<20K) regions of the cloud that account for most of its mass. We are able to derive a single-valued X-factor for all three CO isotopologues in the warm ( Tdust>25 K ) material that is spatially coincident with an HII region surrounding the star LKHa101. We derive LTE CO column densities for 13CO and C18O since we find both lines are relatively optically thin. In the warm cloud material CO is completely in the gas phase and we are able to recover the total 13CO and C18O abundances. Using CO abundances and deep Herschel observations, we measure lower bounds to the freeze-out of CO onto dust across the whole cloud finding some regions having CO depleted by a factor of >20. We construct the first maps of depletion that span the extent of a giant molecular cloud. Using these maps we identify 75 depletion-defined cores and discuss their physical nature.

arXiv comment36 figures

References in corpus (35)

• Astropy: A Community Python Package for Astronomy
• Binary companions of evolved stars in APOGEE DR14: Search method and catalog of ~5,000 companions
• The CO-to-H2 Conversion Factor
• Structural Analysis of Molecular Clouds: Dendrograms
• Bias-free Measurement of Giant Molecular Cloud Properties
• A FUSE Survey of Interstellar Molecular Hydrogen in Translucent Clouds
• CO Isotopologues in the Perseus Molecular Cloud Complex: the X-Factor and Regional Variations
• The relation between gas and dust in the Taurus Molecular Cloud
• The Nature of the Dense Core Population in the Pipe Nebula: Thermal Cores Under Pressure
• 2MASS wide field extinction maps - I. The Pipe nebula
• Desorption rates and sticking coefficients for CO and N2 interstellar ices
• Herschel-Planck dust optical-depth and column-density maps: I. Method description and results for Orion
• Reconstructing the density and temperature structure of prestellar cores from $Herschel$ data: A case study for B68 and L1689B
• Direct Measurement of the Ratio of Carbon Monoxide to Molecular Hydrogen in the Diffuse Interstellar Medium
• The California Molecular Cloud
• The On The Fly Imaging Technique
• NICEST, a near-infrared color excess method tailored for small-scale structures
• Is atomic carbon a good tracer of molecular gas in metal-poor galaxies?
• CO Abundance Variations in the Orion Molecular Cloud
• Mapping Large-Scale CO Depletion in a Filamentary Infrared Dark Cloud
• High abundance ratio of ${}^{13}$CO to C${}^{18}$O toward photon-dominated regions in the Orion-A giant molecular cloud
• The Green Bank Ammonia Survey: Dense Cores Under Pressure in Orion A
• Understanding star formation in molecular clouds III. Probability distribution functions of molecular lines in Cygnus X
• Herschel-Planck dust optical depth and column density maps - II. Perseus
• A First Look at the Auriga-California Giant Molecular Cloud With Herschel and the CSO: Census of the Young Stellar Objects and the Dense Gas
• The CO-to-H2 Conversion Factor across the Perseus Molecular Cloud
• The Relationship Between the Dust and Gas-Phase CO Across the California Molecular Cloud
• The AMANOGAWA-2SB Galactic Plane Survey I: Data on the Galactic Equator
• HP2 survey: III The California Molecular Cloud--A Sleeping Giant Revisited
• Oxygen isotopic ratios in galactic clouds along the line of sight towards Sagittarius B2
• The Spitzer Survey of Interstellar Clouds in the Gould Belt. VI. The Auriga-California Molecular Cloud observed with IRAC and MIPS
• Galactic Chemical Evolution and the Oxygen Isotopic Composition of the Solar System
• Physical properties and chemical composition of the cores in the California molecular cloud
• The Parsec-Scale Relationship Between I_CO and A_V in Local Molecular Clouds
• X Marks the Spot: Nexus of Filaments, Cores, and Outflows in a Young Star-Forming Region

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• The Correlation Between Dust and Gas Contents in Molecular Clouds
• KAgoshima Galactic Object survey with Nobeyama 45-metre telescope by Mapping in Ammonia lines (KAGONMA): Discovery of parsec-scale CO depletion in the Canis Major star-forming region
• CO mapping of Cygnus-X -- volume density distribution
• Extended atomic carbon around molecular clouds
• On volume density and star formation in nearby molecular clouds
• Parallel and Perpendicular Alignments of Velocity Gradient and Magnetic Field observed in the Molecular Clouds L1478 and L1482
• Systematic Investigation of Dust and Gaseous CO in 12 Nearby Molecular Clouds