Census of High- and Medium-mass Protostars V. CO Abundance and the Galactic $X_{\text{CO}}$ Factor

Abstract

We present the second dust continuum data release in the Census of High- and Medium-mass Protostars (CHaMP), expanding the methodology trialed in Pitts et al. 2019 to the entire CHaMP survey area ($280^{\circ }<l<300^{\circ }$, $-4^{\circ }<b<+2^{\circ }$). This release includes maps of dust temperature ($T_d$), H${}_2$ column density ($N_{H_2}$), gas-phase CO abundance, and temperature-density plots for every prestellar clump with Herschel coverage, showing no evidence of internal heating for most clumps in our sample. We show that CO abundance is a strong function of $T_d$, and can be fit with a second-order polynomial in log-space, with a typical dispersion of a factor of 2--3. The CO abundance peaks at $20.0_{-1.0}^{+0.4}$ K with a value of $7.4_{-0.3}^{+0.2}\times 10^{-5}$ per H${}_2$; the low $T_d$ at which this maximal abundance occurs relative to laboratory results is likely due to interstellar UV bombardment in the largest survey fields. Finally, we show that, as predicted by theoretical literature and hinted at in previous studies of individual clouds, the conversion factor from integrated ${}^{12}$CO line intensity ($I_{{}^{12}CO}$) to $N_{H_2}$, the $X_{CO}$-factor, varies as a broken power-law in $I_{{}^{12}CO}$ with a transition zone between 70 and 90 K km${}^{-1}$. The $X_{CO}$-function we propose has $N_{H_2}\propto I_{{}^{12}CO}^{0.51}$ for $I_{{}^{12}CO}\lesssim 70$ K km${}^{-1}$ and $N_{H_2}\propto I_{{}^{12}CO}^{2.3}$ for $I_{{}^{12}CO}\gtrsim 90$ K km${}^{-1}$. The high-$I_{{}^{12}CO}$ side should be generalizable with known adjustments for metallicity, but the influence of interstellar UV fields on the low-$I_{{}^{12}CO}$ side may be sample specific. We discuss how these results expand upon previous works in the CHaMP series, and help tie together observational, theoretical, and laboratory studies on CO over the past decade.

arXiv comment33 pages, 13 figures, 2 tables, 51 pages of appendices; accepted to ApJS (in print)

References in corpus (84)

• Astropy: A Community Python Package for Astronomy
• emcee: The MCMC Hammer
• The Wide-field Infrared Survey Explorer (WISE): Mission Description and Initial On-orbit Performance
• The Global Schmidt Law in Star Forming Galaxies
• Binary companions of evolved stars in APOGEE DR14: Search method and catalog of ~5,000 companions
• Embedded Clusters in Molecular Clouds
• The Photodetector Array Camera and Spectrometer (PACS) on the Herschel Space Observatory
• The Herschel-SPIRE instrument and its in-flight performance
• The CO-to-H2 Conversion Factor
• The Milky Way in Molecular Clouds: A New Complete CO Survey
• Toward Understanding Massive Star Formation
• Trigonometric Parallaxes of Massive Star Forming Regions: VI. Galactic Structure, Fundamental Parameters and Non-Circular Motions
• Clouds, filaments and protostars: the Herschel Hi-GAL Milky Way
• The Dark Molecular Gas
• New Interstellar Dust Models Consistent with Extinction, Emission, and Abundance Constraints
• The AKARI/IRC Mid-Infrared All-Sky Survey
• Hi-GAL: the Herschel infrared Galactic Plane Survey
• A Catalog of Extended Green Objects (EGOs) in the GLIMPSE Survey: A new sample of massive young stellar object outflow candidates
• A Herschel [CII] Galactic plane survey I: the global distribution of ISM gas components
• CO Isotopologues in the Perseus Molecular Cloud Complex: the X-Factor and Regional Variations
• Photodesorption of ices I: CO, N2 and CO2
• The Large APEX Bolometer Camera LABOCA
• The relation between gas and dust in the Taurus Molecular Cloud
• On the Relationship Between Molecular Hydrogen and Carbon Monoxide Abundances in Molecular Clouds
• Evolution and fate of very massive stars
• 2MASS wide field extinction maps - I. The Pipe nebula
• The Milky Way Project First Data Release: A Bubblier Galactic Disk
• Planck Early Results: The Galactic Cold Core Population revealed by the first all-sky survey
• New infrared star clusters in the southern Milky Way with 2MASS
• Modeling CO Emission: I. CO as a Column Density Tracer and the X-Factor in Molecular Clouds
• Modelling CO formation in the turbulent interstellar medium
• The Degree of CO Depletion in Pre-stellar Cores
• The CO-H2 Conversion Factor in Disc Galaxies and Mergers
• A Herschel [C II] Galactic plane survey II: CO-dark H2 in clouds
• Modeling CO Emission: II. The Physical Characteristics that Determine the X factor in Galactic Molecular Clouds
• The 6-GHz methanol multibeam maser catalogue IV: Galactic longitudes 186 to 330 including the Orion-Monoceros region
• A Theory for the Excitation of CO in Star Forming Galaxies
• A Pan-Carina YSO Catalog: Intermediate-Mass Young Stellar Objects in the Carina Nebula Identified Via Mid-Infrared Excess Emission
• Thermal desorption characteristics of CO, O2 and CO2 on non-porous water, crystalline water and silicate surfaces at sub-monolayer and multilayer coverages
• Revisiting the Integrated Star Formation Law. II. Starbursts and the Combined Global Schmidt Law
• Far-Infrared Dust Temperatures and Column Densities of the MALT90 Molecular Clump Sample
• New Galactic Star Clusters Discovered in the VVV Survey
• Evolution of OH and CO-dark Molecular Gas Fraction Across a Molecular Cloud Boundary In Taurus
• The X-factor in Galaxies: I. Dependence on Environment and Scale
• New infrared star clusters and candidates in the Galaxy detected with 2MASS
• The Three-mm Ultimate Mopra Milky Way Survey. I. Survey Overview, Initial Data Releases, and First Results
• CO Abundance Variations in the Orion Molecular Cloud
• Mapping Large-Scale CO Depletion in a Filamentary Infrared Dark Cloud
• High-Mass Cloud Cores in the eta Carinae Giant Molecular Cloud
• Mapping the column density and dust temperature structure of IRDCs with Herschel
• The RMS Survey: Mid-Infrared Observations of Candidate Massive YSOs in the Southern Hemisphere
• HST/ACS H-alpha Imaging of the Carina Nebula: Outflow Activity Traced by Irradiated Herbig-Haro Jets
• X-ray Star Clusters in the Carina Complex
• The X_CO conversion factor from galactic multiphase ISM simulations
• The Galactic Census of High- and Medium-mass Protostars. I. Catalogues and First Results from Mopra HCO+ Maps
• High CO depletion in southern infrared-dark clouds
• Opening the Treasure Chest: A Newborn Star Cluster Emerges from its Dust Pillar in Carina
• Using CO line ratios to trace the physical properties of molecular clouds
• 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
• Characterizing the line emission from molecular clouds. Stratified random sampling of the Perseus cloud
• The Giant Pillars of the Carina Nebula
• HI, CO, and Dust in the Perseus Cloud
• HI filaments are cold and associated with dark molecular gas. HI4PI based estimates of the local diffuse CO-dark H2 distribution
• Variations between Dust and Gas in the Diffuse Interstellar Medium
• The Galactic Census of High- and Medium-mass Protostars. II. Luminosities and Evolutionary States of a Complete Sample of Dense Gas Clumps
• Circumnuclear Multi-phase Gas in Circinus Galaxy I: Non-LTE calculations of CO lines
• Hundreds of new cluster candidates in the VISTA variables in the Via Lactea survey DR1
• CO depletion: a microscopic perspective
• The Galactic Census of High- and Medium-mass Protostars. IV. Molecular Clump Radiative Transfer, Mass Distributions, Kinematics, and Dynamical Evolution
• L-band (3.5 micron) IR-excess in massive star formation, II. RCW 57/NGC 3576
• The environs of the HII region Gum31
• Millimetre-Wave and Near-Infrared Signposts of Massive Molecular Clump Evolution and Star Cluster Formation
• CO-to-H${}_2$ Conversion and Spectral Column Density in Molecular Clouds: The Vriability of $X_{\mathrm{CO}}$ Factor
• The Galactic Census of High- and Medium-mass Protostars. III ${}^{12}$CO Maps and Physical Properties of Dense Clump Envelopes and their Embedding GMCs
• Cooling Rates of Molecular Clouds Based on Numerical MHD Turbulence and non-LTE Radiative Transfer
• X-ray properties of the young open clusters HM1 and IC2944/2948
• Fermi-LAT gamma-ray study of the interstellar medium and cosmic rays in the Chamaeleon Molecular-Cloud Complex: A look at the dark gas as optically thick HI
• On the Diagnostic Power of FIR/Sub-mm SED Fitting in Massive Galactic Molecular Clumps
• Spectroscopy and Linear Spectropolarimetry of the early Herbig Be Stars PDS 27 and PDS 37
• Chandra X-ray observation of the HII region Gum 31 in the Carina Nebula complex
• The HP2 Survey - IV. The Pipe nebula: Effective dust temperatures in dense cores
• Gemini, SOFIA, and ATCA Reveal Very Young, Massive Protostars in the Collapsing Molecular Cloud BYF 73
• HCN hyperfine ratio analysis of massive molecular clumps

Cited by in corpus (5)

• OGHReS: Large-scale filaments in the outer Galaxy
• Linking High- and Low-Mass Star Formation: Observation-Based Continuum Modelling and Physical Conditions
• SOFIA and ALMA Investigate Magnetic Fields and Gas Structures in Massive Star Formation: The Case of the Masquerading Monster in BYF 73
• Water emission tracing active star formation from the Milky Way to high-$z$ galaxies
• The Correlation Between Dust and Gas Contents in Molecular Clouds