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| Paper: |
Molecular Clouds and Star Formation in M51 |
| Volume: |
249, The Central Kiloparsec of Starbursts and AGN: the La Palma Connection |
| Page: |
723 |
| Authors: |
Tosaki, Tomoka; Hasegawa, Takashi; Shioya, Yasuhiro; Kuno, Nario; Matsushita, Satoki |
| Abstract: |
We present high-resolution 13CO (J=1 --> 0) mapping observations of the southern bright arm region of M51, including the galactic center, with the NRO 45m telescope in order to study the physical conditions of the molecular clouds in the arm and the interarm. The map shows the central depression of 13CO (J=1 --> 0) emission, the circumnuclear ring (radius ~10'' -- 20''), and the spiral arm structure. We also find that the 13CO distribution has a depression in a part of spiral arm. The distribution of 13CO shows better correspondence with that of the Hα emission than the 12CO in the disk region except for the central region. The 12CO / 13CO ratio spatially varies, and shows high values (~20) for the interarm and the central region, while low (~10) for the arm. They indicate that there is denser gas in the spiral arm than in the interarm. The 13CO emission is located downstream of the 12CO arm, i.e., there is an offset between the 12CO and the 13CO as well as the Hα emission. This suggests that there is a time delay from an accumulation of gas by density wave to dense gas formation and, accordingly, star formation. This time delay is estimated as ~107 yr on the assumption of the galactic rotation derived from the rotation curve and the pattern speed of the spiral pattern of M51. This is similar to the growth timescale of a gravitational instability in the spiral arm of M51, suggesting that gravitational instability plays an important role in the dense gas formation. |
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