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NRO legacy project: M 33 all disk survey of Giant Molecular Clouds (GMCs) with NRO-45m and ASTE-10m telescopes

  • M. Röllig, R. Simon, V. Ossenkopf, J. Stutzki, T. Tosaki (a1), N. Kuno (a2), S. Onodera (a2), R. Miura (a3), K. Muraoka (a4), T. Sawada (a5), S. Komugi (a5), K. Nakanishi (a1), K. Kohno (a6), R. Kawabe (a2), H. Nakanishi (a7) and N. Arimoto (a5)...

Abstract

We present the results of the Nobeyama Radio Observatory (NRO) M 33 All Disk (30′ × 30′, or 7.3 kpc  ×  7.3 kpc) Survey of Giant Molecular Clouds (NRO MAGiC) based on 12CO(J = 1–0) observations using the NRO 45-m telescope and 12CO(J = 3–2) observations using the ASTE 10-m telescope. The spatial resolution of the resultant 12CO(J = 1–0) map is 193, corresponding to 81 pc, which is sufficient to identify each Giant Molecular Cloud (GMC) in the disk. We found clumpy structures with a typical spatial scale of  ~100 pc, corresponding to GMCs, and no diffuse, smoothly distributed component of molecular gas at this sensitivity.

We obtained a map of the molecular fraction, fmol = ΣH2/(ΣHi + ΣH2), at a 100-pc resolution. This is the first fmol map covering an entire galaxy with a GMC-scale resolution. The correlation between fmol and gas surface density shows two distinct sequences. The presence of two correlation sequences can be explained by differences in metallicity, i.e., higher (~2-fold) metallicity in the central region (r <  1.5 kpc) than in the outer parts. Alternatively, differences in scale height can also account for the two sequences, i.e., increased scale height toward the outer disk.

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[1]Freedman, W.L., Wilson, C.D., & Madore, B.F., 1991, ApJ, 372, 455
[2] Komugi, et al., 2011, ApJ, submitted
[3]Miura, R., et al., 2010, ApJ, 724, 1120
[4]Nakanishi, H., et al., 2006, ApJ, 651, 804
[5]Onodera, S., et al., 2010, ApJ, 722, L127
[6]Scoville, N.Z., & Sanders, D.B., 1987, Interstellar Processes, 134, 21
[7]Tosaki, T., et al., 2007, ApJ, 664, L27
[8] Tosaki, T., et al., 2011, PASJ, submitted

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