AAS 201st Meeting, January, 2003
Session 112. The ISM: Clouds and Regions
Poster, Thursday, January 9, 2003, 9:20am-4:00pm, Exhibit Hall AB

## [112.07] Detection of Molecular Gas in the Interarm Regions of M83

M. Yang, S.D. Lord, A.C.A. Boogert, J.R Brauher, T.G. Phillips (Caltech), R.P.J. Tilanus (Joint Astronomy Center)

The inner eastern spiral arm of the barred starbust galaxy M83 is mapped in the {\rm 12CO~(J=2-1)}~ transition using the Caltech Submillimeter Observatory (CSO). The Nyquist sampled CO map covers a 2.1\prime~\times 3.7\prime~ (3.1~\times~5.4~Mpc) field at a sensitivity Tr*\leq 20 mK in a 32\prime\prime beam. This is the most sensitive CO map of this source taken to date. For the first time, molecular gas is detected in between the well defined spiral arms with high S/N. To further characterize the molecular gas properties, we measured the {\rm 12CO~(J=3-2)} line in a 21\prime\prime beam at 14 positions in both arm and interarm regions.

We compared the molecular gas distribution with other gas and star formation tracers. CO emission coincides closely with HI emission outside the nuclear region, maintaining a nearly constant emission ratio throughout most of the region. On the spiral arm, the CO ridge lies between the HI ridge and the dust lanes. The HI arm is displaced by approximately 8\prime\prime downstream from the CO arm, while the dust lanes run along the inner edge of the CO arm. The CO emission correlates better with the non-thermal emission than with the H\beta emission. This implies cosmic ray heating is a more important contributor to the CO emission brightness than UV heating via star formation. However, the intrinsic molecular gas density remains the dominant factor in determining the CO emission. We further investigate the heating and photodissociation processes along the eastern arm of M83 by combining our CO observations with ISO C[II], O[I] and far-infrared continuum maps.