ACA CO($J=2-1$) Mapping of the Nearest Spiral Galaxy M33. I. Initial Results and Identification of Molecular Clouds

Abstract

We present the results of ALMA-ACA 7 m-array observations in ${}^{12}$CO($J=2-1$), ${}^{13}$CO($J=2-1$), and C${}^{18}$O($J=2-1$) line emission toward the molecular-gas disk in the Local Group spiral galaxy M33 at an angular resolution of 7".31 $\times$ 6".50 (30 pc $\times$ 26 pc). We combined the ACA 7 m-array ${}^{12}$CO($J=2-1$) data with the IRAM 30 m data to compensate for emission from diffuse molecular-gas components. The ACA+IRAM combined ${}^{12}$CO($J=2-1$) map clearly depicts the cloud-scale molecular-gas structure over the M33 disk. Based on the ACA+IRAM ${}^{12}$CO($J=2-1$) cube data, we cataloged 848 molecular clouds with a mass range from $10^3$ $M_{\odot }$ to $10^6$ $M_{\odot }$. We found that high-mass clouds ($\ge 10^5{M}_{\odot }$) tend to associate with the $8\mu$m-bright sources in the spiral arm region, while low-mass clouds ($<10^5{M}_{\odot }$) tend to be apart from such $8\mu$m-bright sources and to exist in the inter-arm region. We compared the cataloged clouds with GMCs observed by the IRAM 30 m telescope at 49 pc resolution (IRAM GMC: Corbelli et al. 2017), and found that a small IRAM GMC is likely to be identified as a single molecular cloud even in ACA+IRAM CO data, while a large IRAM GMC can be resolved into multiple ACA+IRAM clouds. The velocity dispersion of a large IRAM GMC is mainly dominated by the line-of-sight velocity difference between small clouds inside the GMC rather than the internal cloud velocity broadening.

arXiv comment23 pages, 17 figures, accepted for publication in the Astrophysical Journal

References in corpus (65)

• The Astropy Project: Building an inclusive, open-science project and status of the v2.0 core package
• The CO-to-H2 Conversion Factor
• The Calibration of Mid-Infrared Star Formation Rate Indicators
• Structural Analysis of Molecular Clouds: Dendrograms
• The Resolved Properties of Extragalactic Giant Molecular Clouds
• The Spitzer Local Volume Legacy: Survey Description and Infrared Photometry
• Star Formation in NGC5194 (M51a): The Panchromatic View from GALEX to Spitzer
• A Survey of Local Group Galaxies Currently Forming Stars. I. UBVRI Photometry of Stars in M31 and M33
• Physical properties of molecular clouds for the entire Milky Way disk
• Massive Stars: Their Environment and Formation
• The warm ionized medium in spiral galaxies
• Bias-free Measurement of Giant Molecular Cloud Properties
• The Second Survey of the Molecular Clouds in the Large Magellanic Cloud by NANTEN. II. Star Formation
• The Second Survey of the Molecular Clouds in the Large Magellanic Cloud by NANTEN I: Catalog of Molecular Clouds
• The PdBI Arcsecond Whirlpool Survey (PAWS): Environmental Dependence of Giant Molecular Cloud Properties in M51
• The PdBI Arcsecond Whirlpool Survey (PAWS). I. A Cloud-Scale/Multi-Wavelength View of the Interstellar Medium in a Grand-Design Spiral Galaxy
• Giant Molecular Clouds in M33 - I. BIMA All Disk Survey
• Pah and Mid-IR Luminosities as Measures of Star-Formation Rate in Spitzer First Look Survey Galaxies
• The Mass Spectra of Giant Molecular Clouds in the Local Group
• A Comparative Study of Giant Molecular Clouds in M51, M33 and the Large Magellanic Cloud
• The Plateau de Bure + 30m Arcsecond Whirlpool Survey reveals a thick disk of diffuse molecular gas in the M51 galaxy
• A Survey of Local Group Galaxies Currently Forming Stars: III. A Search for Luminous Blue Variables and Other H-alpha Emission-Lined Stars
• Molecular and Atomic Gas in the Local Group Galaxy M33
• Breakdown of Kennicutt-Schmidt Law at GMC Scales in M33
• Giant Molecular Cloud Catalogues for PHANGS-ALMA: Methods and Initial Results
• High Resolution Molecular Gas Maps of M33
• New Constraints on the ${}^{12}$CO(2-1)/(1-0) Line Ratio Across Nearby Disc Galaxies
• A Mapping Survey of the 12CO and 13CO Emission in Galaxies
• Giant Molecular Clouds in the Local Group Galaxy M33
• The Super-linear Slope of the Spatially-Resolved Star Formation Law in NGC 3521 and NGC 5194 (M51a)
• HIIphot: Automated Photometry of HII Regions Applied to M51
• Low-J CO Line Ratios From Single Dish CO Mapping Surveys and PHANGS-ALMA
• From molecules to Young Stellar Clusters: the star formation cycle across the M33 disk
• AUTO-MULTITHRESH: A General Purpose Automasking Algorithm
• The distance of M33 and the stellar population in its outskirts
• Full-disc ${}^{13}$CO(1-0) mapping across nearby galaxies of the EMPIRE survey and the CO-to-H${}_2$ conversion factor
• GMC Evolutions in the Nearby Spiral Galaxy M33
• Dynamical signatures of a LCDM-halo and the distribution of the baryons in M33
• CO Multi-line Imaging of Nearby Galaxies (COMING). IX. ${}^{12}$CO($J$=2-1)/${}^{12}$CO($J$=1-0) line ratio on kiloparsec scales
• Kinematics of the Atomic ISM in M33 on 80 pc scales
• Quantifying non-star formation associated 8um dust emission in NGC 628
• Properties and rotation of molecular clouds in M 33
• Evolutionary Description of Giant Molecular Cloud Mass Functions on Galactic Disks
• The AMANOGAWA-2SB Galactic Plane Survey I: Data on the Galactic Equator
• NRO M33 All Disk Survey of Giant Molecular Clouds (NRO MAGiC): I. HI to H_2 Transition
• Relations Between Molecular Cloud Structure Sizes and Line Widths in the Large Magellanic Cloud
• Giant Molecular Clouds in the Spiral Arm of IC 342
• Molecular Gas Evolution across a Spiral Arm in M 51
• ALMA Observations of a Quiescent Molecular Cloud in the Large Magellanic Cloud
• Star Formation Induced by Cloud-Cloud Collisions and Galactic Giant Molecular Cloud Evolution
• CO Multi-line Imaging of Nearby Galaxies (COMING): I. Physical properties of molecular gas in the barred spiral galaxy NGC 2903
• ALMA CO Observations of a Giant Molecular Cloud in M33: Evidence for High-Mass Star Formation Triggered by Cloud-Cloud Collisions
• The molecular gas mass of M33
• A CO isotopologue Line Atlas within the Whirlpool galaxy Survey (CLAWS)
• ALMA Observations of Giant Molecular Clouds in M33 I: Resolving Star Formation Activities in the Giant Molecular Filaments Possibly Formed by a Spiral Shock
• CO Multi-line Imaging of Nearby Galaxies (COMING). III. Dynamical effect on molecular gas density and star formation in the barred spiral galaxy NGC 4303
• An Unbiased CO Survey Toward the Northern Region of the Small Magellanic Cloud with the Atacama Compact Array. I. Overview: CO Cloud Distributions
• CARMA Survey toward Infrared-bright Nearby Galaxies (STING). IV. Spatially Resolved 13CO in Spiral Galaxies
• Enhancement of CO(3-2)/CO(1-0) Ratios and Star Formation Efficiencies in Supergiant HII Regions
• ALMA Observations of Giant Molecular Clouds in M33. II. Triggered High-mass Star Formation by Multiple Gas Colliding Events at the NGC 604 Complex
• An Unbiased CO Survey Toward the Northern Region of the Small Magellanic Cloud with the Atacama Compact Array. II. CO Cloud Catalog
• NRO M33 All-Disk Survey of Giant Molecular Clouds (NRO MAGiC): II. Dense Gas Formation within Giant Molecular Clouds in M33
• ALMA Observations of Giant Molecular Clouds in M33 III: Spatially Resolved Features of the Star-Formation Inactive Million-solar-mass Cloud
• CO Multi-line Imaging of Nearby Galaxies (COMING). X. Physical conditions of molecular gas and the local SFR-Mass relation
• Molecular Line Ratio Diagnostics Along the Radial Cut and Dusty UV-bright Clumps in a Spiral Galaxy NGC 0628

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• The Karl G. Jansky Very Large Array Local Group L-band Survey (LGLBS)
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