Other
Scientific paper
Jan 2009
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2009aas...21344301e&link_type=abstract
American Astronomical Society, AAS Meeting #213, #443.01; Bulletin of the American Astronomical Society, Vol. 41, p.323
Other
Scientific paper
We present results from an application of a method for deriving the star formation timescale and pattern speed, which utilizes offsets between molecular and young-stellar spiral arms, to nearby spiral galaxies.
From CO and H-alpha images of 12 nearby spiral galaxies, we could derive the parameters for 4 galaxies. For these galaxies, the derived timescale for star formation is roughly consistent to the free-fall time of typical molecular clouds, which indicates that the gravitational instability is a dominant mechanism to trigger star formations in spiral arms. A radius for the corotation resonance is calculated from the derived pattern speed and is almost the same as that of molecular disk, and about half of the optical radius.
We also find that other 2 galaxies show no offsets between CO and H-alpha arms, although they are clearly traced. A presence of a bar could account for this feature, since these 2 galaxies are both barred.
Offsets of remaining 6 galaxies are found to be ambiguous. In other words, their dependence on the rotational frequency cannot be explained by our model, or the number or quality of data is not sufficient for the analysis. Possible explanations for this ambiguity are peculiarity of galaxies (e.g., weak density waves), and/or quality of CO data is not enough to detect arms and offsets clearly. The former is supported by our finding that an arm strength of these 6 galaxies estimated from the K-band image is weaker than that of 4 galaxies, whose star formation timescale and pattern speed are derived.
A part of this study is supported by the Japan Society for the Promotion of Science and the MEXT Grant-in-Aid for Scientific Research.
Egusa Fumi
Kohno Kotaro
Komugi Shinya
Nakanishi Hiizu
Sofue Yoshiaki
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