First Resolved Dust Continuum Measurements of Individual Giant Molecular Clouds in the Andromeda Galaxy

Abstract

In our local Galactic neighborhood, molecular clouds are best studied using a combination of dust measurements, to determine robust masses, sizes and internal structures of the clouds, and molecular-line observations to determine cloud kinematics and chemistry. We present here the first results of a program designed to extend such studies to nearby galaxies beyond the Magellanic Clouds. Utilizing the wideband upgrade of the Submillimeter Array (SMA) at 230 GHz we have obtained the first continuum detections of the thermal dust emission on sub-GMC scales ($\sim$ 15 pc) within the Andromeda galaxy (M31). These include the first resolved continuum detections of dust emission from individual GMCs beyond the Magellanic Clouds. Utilizing a powerful capability of the SMA, we simultaneously recorded CO(2-1) emission with identical $(u,v)$ coverage, astrometry and calibration, enabling the first measurements of the CO conversion factor, ${\alpha }_{\mathrm{CO}(2-1)}$, toward individual GMCs across an external galaxy. Our direct measurement yields an average CO--to--dust mass conversion factor of ${\alpha }_{\mathrm{CO}-\mathrm{dust}}^{\prime }=0.042\pm 0.018$ $M_{\odot }$ (K km s${}^{-1}$ pc${}^2$)${}^{-1}$ for the $J=2-1$ transition. This value does not appear to vary with galactocentric radius. Assuming a constant gas-to-dust ratio of 136, the resulting ${\alpha }_{\mathrm{CO}}$ $=$ 5.7 $\pm$ 2.4 $M_{\odot }$ (K km s${}^{-1}$ pc${}^2$)${}^{-1}$ for the 2-1 transition is in excellent agreement with that of Milky Way GMCs, given the uncertainties. Finally, using the same analysis techniques, we compare our results with observations of the local Orion molecular clouds, placed at the distance of M31 and simulated to appear as they would if observed by the SMA.

arXiv commentApJ, in press

References in corpus (39)

• Cosmic Star Formation History
• The CO-to-H2 Conversion Factor
• Mass and environment as drivers of galaxy evolution in SDSS and zCOSMOS and the origin of the Schechter function
• From filamentary clouds to prestellar cores to the stellar IMF: Initial highlights from the Herschel Gould Belt survey
• Planck 2013 results. XI. All-sky model of thermal dust emission
• The distance to the Orion Nebula
• Characterizing interstellar filaments with Herschel in IC5146
• On the Star Formation Rates in Molecular Clouds
• The CO-to-H2 Conversion Factor From Infrared Dust Emission Across the Local Group
• Improved Estimates of the Milky Way's Stellar Mass and Star Formation Rate from Hierarchical Bayesian Meta-Analysis
• The Star Formation Rate and Gas Surface Density Relation in the Milky Way: Implications for Extragalactic Studies
• The mass function of dense molecular cores and the origin of the IMF
• Probing the evolution of molecular cloud structure: From quiescence to birth
• The global dust modelling framework THEMIS (The Heterogeneous dust Evolution Model for Interstellar Solids)
• The Aquila prestellar core population revealed by Herschel
• The PdBI Arcsecond Whirlpool Survey (PAWS): Environmental Dependence of Giant Molecular Cloud Properties in M51
• Star Formation Relations in Nearby Molecular Clouds
• Herschel-Planck dust optical-depth and column-density maps: I. Method description and results for Orion
• The "True" Column Density Distribution in Star-Forming Molecular Clouds
• Planck 2013 results. IX. HFI spectral response
• Spitzer/MIPS Infrared Imaging of M31: Further Evidence for a Spiral/Ring Composite Structure
• Molecular gas in the Andromeda galaxy
• Star Formation in Massive Clusters via the Wilkinson Microwave Anisotropy Probe and the Spitzer Glimpse Survey
• The California Molecular Cloud
• An almost head-on collision as the origin of two off-centre rings in the Andromeda galaxy
• Revealing the physical properties of molecular gas in Orion with a large scale survey in J=2-1 lines of 12CO, 13CO and C18O
• Molecular clouds have power-law probability distribution functions
• Larson's third law and the universality of molecular cloud structure
• Dust variations in the diffuse interstellar medium: constraints on Milky Way dust from Planck-HFI observations
• Schmidt's Conjecture and Star Formation in Molecular Clouds
• The Herschel Exploitation of Local Galaxy Andromeda (HELGA). I: Global far-infrared and sub-mm morphology
• Chandra ACIS Survey of X-ray Point Sources: The Source Catalog
• The Herschel Exploitation of Local Galaxy Andromeda (HELGA) VII: A SKIRT radiative transfer model and insights on dust heating
• The ALMA view of GMCs in NGC 300: Physical Properties and Scaling Relations at 10 pc Resolution
• The Initial Conditions of Stellar Protocluster Formation: III. The Herschel counterparts of the Spitzer Dark Cloud catalogue
• The Herschel Exploitation of Local Galaxy Andromeda (HELGA). VI. The distribution and properties of molecular cloud associations in M31
• The Dust in M31
• Spitzer Photometry of ~1 Million Stars in M31 and 15 Other Galaxies
• Gathering dust: A galaxy-wide study of dust emission from cloud complexes in NGC 300

Cited by in corpus (2)

• Simultaneous Deep Measurements of CO isotopologues and Dust Emission in Giant Molecular Clouds in the Andromeda Galaxy
• Systematic Investigation of Dust and Gaseous CO in 12 Nearby Molecular Clouds