MOLECULAR GAS EVOLUTION ACROSS A SPIRAL ARM IN M51

Journal Article · Mon Jan 10 04:00:00 EST 2011 · Astrophysical Journal

DOI:https://doi.org/10.1088/0004-637X/726/2/85· OSTI ID:21567663

Egusa, Fumi; Scoville, Nick ^[1]; Koda, Jin ^[2]

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1. California Institute of Technology, MS 249-17 Pasadena, CA 91125 (United States)
2. SUNY Stony Brook, Stony Brook, NY 11794 (United States)

We present sensitive and high angular resolution CO(1-0) data obtained by the Combined Array for Research in Millimeter-wave Astronomy observations toward the nearby grand-design spiral galaxy M51. The angular resolution of 0.''7 corresponds to 30 pc, which is similar to the typical size of giant molecular clouds (GMCs), and the sensitivity is also high enough to detect typical GMCs. Within the 1' field of view centered on a spiral arm, a number of GMC-scale structures are detected as clumps. However, only a few clumps are found to be associated with each giant molecular association (GMA) and more than 90% of the total flux is resolved out in our data. Considering the high sensitivity and resolution of our data, these results indicate that GMAs are not mere confusion with GMCs but plausibly smooth structures. In addition, we have found that the most massive clumps are located downstream of the spiral arm, which suggests that they are at a later stage of molecular cloud evolution across the arm and plausibly are cores of GMAs. By comparing with H{alpha} and Pa{alpha} images, most of these cores are found to have nearby star-forming regions. We thus propose an evolutionary scenario for the interstellar medium, in which smaller molecular clouds collide to form smooth GMAs at spiral arm regions and then star formation is triggered in the GMA cores. Our new CO data have revealed the internal structure of GMAs at GMC scales, finding the most massive substructures on the downstream side of the arm in close association with the brightest H II regions.

• OSTI ID: 21567663
• Journal Information: Astrophysical Journal, Journal Name: Astrophysical Journal Journal Issue: 2 Vol. 726; ISSN ASJOAB; ISSN 0004-637X
• Country of Publication: United States
• Language: English

Related Subjects

79 ASTRONOMY AND ASTROPHYSICS
CARBON COMPOUNDS
CARBON MONOXIDE
CARBON OXIDES
CHALCOGENIDES
CLOUDS
EVOLUTION
GALAXIES
OXIDES
OXYGEN COMPOUNDS