ALMA Observations of Giant Molecular Clouds in M33. II. Triggered High-mass Star Formation by Multiple Gas Colliding Events at the NGC 604 Complex

Abstract

We present the results of ALMA observations in ${}^{12}$CO($J=2-1$), ${}^{13}$CO($J=2-1$), and C${}^{18}$O($J=2-1$) lines and 1.3 mm continuum emission toward a massive ($\sim 10^6{M}_{\odot }$) giant molecular cloud associated with the giant H II region NGC 604 in one of the nearest spiral galaxy M33 at an angular resolution of 0''.44 $\times$ 0''.27 (1.8 pc $\times$ 1.1 pc). The ${}^{12}$CO and ${}^{13}$CO images show highly complicated molecular structures composed of a lot of filaments and shells whose lengths are 5 -- 20 pc. We found three 1.3 mm continuum sources as dense clumps at edges of two shells and also at an intersection of several filaments. We examined the velocity structures of ${}^{12}$CO($J=2-1$) emission in the shells and filaments containing dense clumps, and concluded that expansion of the H II regions cannot explain the formation of such dense cores. Alternatively, we suggest that cloud--cloud collisions induced by an external H I gas flow and the galactic rotation compressed the molecular material into dense filaments/shells as ongoing high-mass star formation sites. We propose that multiple gas converging/colliding events with a velocity of a few tens km s${}^{-1}$ are necessary to build up NGC 604, the most significant cluster-forming complex in the Local Group of galaxies.

15 pages, 8 figures, accepted for publication in The Astrophysical Journal

References in corpus (18)

• Theory of Star Formation
• Filamentary structure of star-forming complexes
• Dawes Review 4: Spiral Structures in Disc Galaxies
• Do cloud-cloud collisions trigger high-mass star formation? I. Small cloud collisions
• Revealing the physical properties of molecular gas in Orion with a large scale survey in J=2-1 lines of 12CO, 13CO and C18O
• The frequency and nature of `cloud-cloud collisions' in galaxies
• Cloud-cloud collision as a trigger of the high-mass star formation; a molecular line study in RCW120
• AUTO-MULTITHRESH: A General Purpose Automasking Algorithm
• High abundance ratio of ${}^{13}$CO to C${}^{18}$O toward photon-dominated regions in the Orion-A giant molecular cloud
• High-resolution radio continuum survey of M33: III. Magnetic fields
• Dynamical signatures of a LCDM-halo and the distribution of the baryons in M33
• Spitzer View of Young Massive Stars in the LMC HII Complexes. II. N159
• Sub-millimeter Observations of Giant Molecular Clouds in the Large Magellanic Cloud: Temperature and Density as Determined from J=3-2 and J=1-0 transitions of CO
• ALMA view of G0.253+0.016: Can cloud-cloud collision form the cloud?
• The role of Galactic HII regions in the formation of filaments. High-resolution submilimeter imaging of RCW 120 with ArTéMiS
• The effect of photoionising feedback on star formation in isolated and colliding clouds
• Supernova Remnants in M33: X-ray Properties as Observed by XMM-Newton
• Enhancement of CO(3-2)/CO(1-0) Ratios and Star Formation Efficiencies in Supergiant HII Regions

Cited by in corpus (13)

• An Unbiased CO Survey Toward the Northern Region of the Small Magellanic Cloud with the Atacama Compact Array. I. Overview: CO Cloud Distributions
• An ALMA study of the massive molecular clump N159W-North in the Large Magellanic Cloud: A possible gas flow penetrating one of the most massive protocluster systems in the Local Group
• An ALMA Glimpse of Dense Molecular Filaments Associated with High-mass Protostellar Systems in the Large Magellanic Cloud
• ALMA reveals a cloud-cloud collision that triggers star formation in N66N of the Small Magellanic Cloud
• Connection among environment, cloud-cloud collision speed, and star formation activity in the strongly barred galaxy NGC1300
• ALMA Observations of Giant Molecular Clouds in M33 III: Spatially Resolved Features of the Star-Formation Inactive Million-solar-mass Cloud
• ACA CO($J=2-1$) Mapping of the Nearest Spiral Galaxy M33. I. Initial Results and Identification of Molecular Clouds
• Massive young stellar objects in the Local Group spiral galaxy M33 identified using machine learning
• Giant molecular clouds and their Type classification in M74: Toward understanding star formation and cloud evolution
• ACA CO(J=2-1) Mapping of the Nearest Spiral Galaxy M33. II. Exploring the Evolution of Giant Molecular Clouds
• ALMA ${}^{13}\mathrm{CO}$(J=1-0) Observations of NGC 604 in M33: Physical Properties of Molecular Clouds
• CH${}_3$OH as a User-Friendly Density Probe: Calibration and Beyond
• Molecular cloud matching in CO and dust in M33 II. Physical properties of giant molecular clouds