GIANT MOLECULAR CLOUD EVOLUTIONS IN THE NEARBY SPIRAL GALAXY M33

• Published in: The Astrophysical journal Vol. 761; no. 1; pp. 1 - 23
• Main Authors: MIURA, Rie E, KOHNO, Kotaro, MINAMIDANI, Tetsuhiro, KOMUGI, Shinya, NAKANISHI, Kouichiro, SAWADA, Tsuyoshi, KANEKO, Hiroyuki, KAWABE, Ryohei, TOSAKI, Tomoka, ESPADA, Daniel, HWANG, Narae, KUNO, Nario, OKUMURA, Sachiko K, HIROTA, Akihiko, MURAOKA, Kazuyuki, ONODERA, Sachiko
• Format: Journal Article
• Language: English
• Published: Bristol IOP 10.12.2012
• Subjects: Astronomical models; ASTRONOMY; ASTROPHYSICS; ASTROPHYSICS, COSMOLOGY AND ASTRONOMY; Categories; COMPARATIVE EVALUATIONS; DENSITY; Earth, ocean, space; Estimates; Evolutionary; Exact sciences and technology; GALAXIES; H II regions; H2 REGIONS; LIFETIME; MASS; Massive stars; Molecular clouds; MOLECULES; SENSITIVITY; SPATIAL RESOLUTION; STAR EVOLUTION; STAR MODELS; STARS; TELESCOPES; galaxies: individual (M33); Giant molecular cloud; Stellar evolution; Star models; HII regions; Massive stars; Lifetime; Star formation; ISM: molecules; Dense gas; submillimeter: ISM; Astronomical catalogues; High field; ISM: clouds; Spiral galaxies; Age
• ISSN: 0004-637X; 1538-4357
• DOI: 10.1088/0004-637x/761/1/37

We present a giant molecular cloud (GMC) catalog of M33, containing 71 GMCs in total, based on wide-field and high-sensitivity CO(J = 3-2) observations with a spatial resolution of 100 pc using the ASTE 10 m telescope. Employing archival optical data, we identify 75 young stellar groups (YSGs) from the excess of the surface stellar density, and estimate their ages by comparing with stellar evolution models. A spatial comparison among the GMCs, YSGs, and H II regions enable us to classify GMCs into four categories: Type A, showing no sign of massive star formation (SF); Type B, being associated only with H II regions; Type C, with both H II regions and <10 Myr old YSGs; and Type D, with both H II regions and 10-30 Myr YSGs. Out of 65 GMCs (discarding those at the edges of the observed fields), 1 (1%), 13 (20%), 29 (45%), and 22 (34%) are Types A, B, C, and D, respectively. We interpret these categories as stages in a GMC evolutionary sequence. Assuming that the timescale for each evolutionary stage is proportional to the number of GMCs, the lifetime of a GMC with a mass >10 super(5) M sub([middot in circle]) is estimated to be 20-40 Myr. In addition, we find that the dense gas fraction as traced by the CO(J = 3-2)/CO(J = 1-0) ratio is enhanced around SF regions. This confirms a scenario where dense gas is preferentially formed around previously generated stars, and will be the fuel for the next stellar generation. In this way, massive SF gradually propagates in a GMC until gas is exhausted.