Variation of Molecular Gas Properties Across the Spiral Arms in IC 342: Large-Scale 13CO (1-0) Emission

Details Variation of Molecular Gas Properties Across the Spiral Arms in IC 342: Large-Scale 13CO (1-0) Emission Variation of Molecular Gas Properties Across the Spiral Arms in IC 342: Large-Scale 13CO (1-0) Emission

Oct 2010

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2010pasj...62.1261h&link_type=abstract

Publications of the Astronomical Society of Japan, Vol.62, No.5, pp.1261-1275

Astronomy and Astrophysics

Astronomy

1

Galaxies: Individual (Ic 342), Galaxies: Ism, Galaxies: Spiral, Ism: Molecules

Scientific paper

We present a 13CO (1-0) mapping survey of the nearby galaxy IC 342 carried out with the Nobeyama 45 m radio telescope. The map covers a 320'' × 320'' region, including its center, bar, and most of one of the spiral arms. The 13CO (1-0) data were compared with 12CO (1-0), Hα, 24μm, and Ks-band images to investigate spatial relations among molecular clouds, star-forming regions, and the stellar potential. The line ratio between both CO lines, I[13CO (1-0)]/I[12CO (1-0)] ≡ R13/12, was also derived to investigate the variation of molecular gas properties. The mean value of R13/12 in the center of IC 342 is low (˜0.10 ± 0.01) compared to the disk region (˜0.15 ± 0.01). While R13/12, in the central region is rather uniform, significant variations of R13/12 were found in the spiral arms; that is, while it is low (˜0.1) at both ends of the bar and at the giant molecular cloud association (GMA) found in the spiral arm, it is high (0.14-0.20) downstream from the low R13/12 region. The low- and high-R13/12 regions in the disk correspond to the 12CO peak and star-forming regions, respectively. The low R13/12 in the galactic center is likely due to the higher gas temperature in the starburst region. The most probable explanation of the R13/12 variation in the disk is that a low R13/12 in the GMA and the ends of the bar reflects an increased fraction of the diffuse molecular component, which has a low column density and low volume density. Around the GMA and the north end of the bar, not only are the star-forming regions downstream from the CO distributions, but R13/12 is also higher downstream, implying the presence of gas compression and ionized/molecular gas spatial offsets, as predicted by density wave models.

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