Simultaneous Deep Measurements of CO isotopologues and Dust Emission in Giant Molecular Clouds in the Andromeda Galaxy

Abstract

We present simultaneous measurements of emission from dust continuum at 230 GHz and the J=2-1 ${}^{12}$CO, ${}^{13}$CO and C${}^{18}$O isotopologues at $\sim$ 15 pc resolution from individual Giant Molecular Clouds (GMCs) in the Andromeda galaxy (M31). These observations were obtained in an ongoing survey of this galaxy being conducted with the Submillimeter Array (SMA). Initial results describing the continuum and ${}^{12}$CO emission were published earlier. Here we primarily analyze the observations of ${}^{13}$CO and C${}^{18}$O emission and compare them to the measurements of dust continuum and ${}^{12}$CO emission. We also report additional dust continuum and CO measurements from newly added GMCs to the M31 sample. We detect spatially resolved ${}^{13}$CO emission with high signal-to-noise in 31 objects. We find the extent of the ${}^{13}$CO emission to be nearly comparable to that of ${}^{12}$CO, typically covering 75\% of the area of the ${}^{12}$CO emission. We derive ${}^{13}$CO and C${}^{18}$O abundances of 2.9 $\times 10^{-6}$ and 4.4 $\times 10^{-7}$ relative to H${}_2$, respectively, by comparison with hydrogen column densities of the same regions derived from the dust continuum observations assuming a Milky Way gas-to-dust ratio. We find the isotopic abundance ratio [${}^{13}$CO]/[C${}^{18}$O] = 6.7$\pm$2.9 to be consistent with the Milky Way value (8.1). Finally, we derive the mass-to-light conversion factors for all three CO species to be ${\alpha }_{12}=8.7\pm 3.9$, ${\alpha }_{13}=48.9\pm 20.4$ and ${\alpha }_{18}=345_{-31}^{+25}$ M${}_{\odot }$ (K km s${}^{-1}$pc${}^2$)${}^{-1}$ for the J=2-1 transitions of ${}^{12}$CO, ${}^{13}$CO and C${}^{18}$O, respectively.

arXiv comment24 pages, 11 figures, accepted for publication in The Astrophysical Journal

References in corpus (28)

• Astropy: A Community Python Package for Astronomy
• The CO-to-H2 Conversion Factor
• On the Star Formation Rates in Molecular Clouds
• The CO-to-H2 Conversion Factor From Infrared Dust Emission Across the Local Group
• Andromeda's Dust
• A FUSE Survey of Interstellar Molecular Hydrogen in Translucent Clouds
• The global dust modelling framework THEMIS (The Heterogeneous dust Evolution Model for Interstellar Solids)
• Star Formation Rates in Molecular Clouds and the Nature of the Extragalactic Scaling Relations
• CO Isotopologues in the Perseus Molecular Cloud Complex: the X-Factor and Regional Variations
• The PdBI Arcsecond Whirlpool Survey (PAWS). I. A Cloud-Scale/Multi-Wavelength View of the Interstellar Medium in a Grand-Design Spiral Galaxy
• The "True" Column Density Distribution in Star-Forming Molecular Clouds
• A Uniform Catalog of Molecular Clouds in the Milky Way
• The Herschel Exploitation of Local Galaxy Andromeda (HELGA) II: Dust and Gas in Andromeda
• Revealing the physical properties of molecular gas in Orion with a large scale survey in J=2-1 lines of 12CO, 13CO and C18O
• Larson's third law and the universality of molecular cloud structure
• ALMA Resolves 30 Doradus: Sub-parsec Molecular Cloud Structure Near the Closest Super-Star Cluster
• Physical Properties of Molecular Clouds at 2 parsec Resolution in the Low-Metallicity Dwarf Galaxy NGC 6822 and the Milky Way
• The ALMA view of GMCs in NGC 300: Physical Properties and Scaling Relations at 10 pc Resolution
• Multi-Transition Study of M51's Molecular Gas Spiral Arms
• ${}^{13}$CO/C${}^{18}$O Gradients Across the Disks of Nearby Spiral Galaxies
• Molecular Gas in SAURON Early-Type Galaxies: Detection of 13CO and HCN Emission
• C18O, 13CO, and 12CO abundances and excitation temperatures in the Orion B molecular cloud: An analysis of the precision achievable when modeling spectral line within the Local Thermodynamic Equilibrium approximation
• ALMA ${}^{12}$CO (J=1--0) imaging of the nearby galaxy M83: Variations in the efficiency of star formation in giant molecular clouds
• The Herschel Exploitation of Local Galaxy Andromeda (HELGA). VI. The distribution and properties of molecular cloud associations in M31
• ALMA Observations of Giant Molecular Clouds in M33 I: Resolving Star Formation Activities in the Giant Molecular Filaments Possibly Formed by a Spiral Shock
• Probing the Cold Deep Depths of the California Molecular Cloud: The Icy Relationship between CO and Dust
• Dense gas tracing the collisional past of Andromeda. An atypical inner region?
• First Resolved Dust Continuum Measurements of Individual Giant Molecular Clouds in the Andromeda Galaxy

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• Systematic Investigation of Dust and Gaseous CO in 12 Nearby Molecular Clouds