MULTI-TRANSITION STUDY OF M51'S MOLECULAR GAS SPIRAL ARMS

Journal Article · Fri Aug 20 00:00:00 EDT 2010 · Astrophysical Journal

DOI:https://doi.org/10.1088/0004-637X/719/2/1588· OSTI ID:21457068

Schinnerer, E ^[1]; Weiss, A ^[2]; Aalto, S ^[3]; Scoville, N Z ^[4]

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1. MPI for Astronomy, Koenigstuhl 17, 69117 Heidelberg (Germany)
2. MPI for Radioastronomy, Auf dem Huegel 69, 53121 Bonn (Germany)
3. Department of Radio and Space Science, Chalmers University of Technology, SE-412 96 Goeteborg (Sweden)
4. California Institute of Technology, MC 249-17, Pasadena, CA 91125 (United States)

Two selected regions in the molecular gas spiral arms in M51 were mapped with the Owens Valley Radio Observatory (OVRO) mm-interferometer in the {sup 12}CO(2-1), {sup 13}CO(1-0), C{sup 18}O(1-0), HCN(1-0), and HCO+(1-0) emission lines. The CO data have been combined with the {sup 12}CO(1-0) data from Aalto et al. covering the central 3.5 kpc to study the physical properties of the molecular gas. All CO data cubes were short spacing corrected using IRAM 30 m ({sup 12}CO(1-0): NRO 45 m) single-dish data. A large velocity gradient analysis finds that the giant molecular clouds (GMCs) are similar to Galactic GMCs when studied at 180 pc (120 pc) resolution with an average kinetic temperature of T{sub kin} = 20(16) K and H{sub 2} density of n(H{sub 2}) = 120(240) cm{sup -3} when assuming virialized clouds (a constant velocity gradient dv/dr). The associated conversion factor between H{sub 2} mass and CO luminosity is close to the Galactic value for most regions analyzed. Our findings suggest that the GMC population in the spiral arms of M51 is similar to those of the Milky Way and therefore the strong star formation occurring in the spiral arms has no strong impact on the molecular gas in the spiral arms. Extinction inferred from the derived H{sub 2} column density is very high (A{sub V} about 15-30 mag), about a factor of 5-10 higher than the average value derived toward H II regions. Thus, a significant fraction of the ongoing star formation could be hidden inside the dust lanes of the spiral arms. A comparison of MIPS 24 {mu}m and H{alpha} data, however, suggests that this is not the case and most of the GMCs studied here are not (yet) forming stars. We also present low (4.''5) resolution OVRO maps of the HCN(1-0) and HCO+(1-0) emission at the location of the brightest {sup 12}CO(1-0) peak.

• OSTI ID: 21457068
• Journal Information: Astrophysical Journal, Journal Name: Astrophysical Journal Journal Issue: 2 Vol. 719; ISSN ASJOAB; ISSN 0004-637X
• Country of Publication: United States
• Language: English

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