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Dense gas formation triggered by spiral density wave in M31

Published online by Cambridge University Press:  01 August 2006

T. Tosaki ,
Y. Shioya ,
N. Kuno ,
K. Nakanishi ,
T. Hasegawa ,
S. Matsushita ,
K. Kohno ,
R. Miura ,
Y. Tamura  and
S. K. Okumura
...Show all authors
T. Tosaki
Affiliation:
Nobeyama Radio Observatory, Minamimaki, Minamisaku, Nagano, 384-1805, Japan email: [email protected]
Y. Shioya
Affiliation:
Physics Department, Graduate School of Science and Engineering, Ehime University, 2-5 Bunkyo-cho, Matsuyama, Ehime 790-8577
N. Kuno
Affiliation:
Nobeyama Radio Observatory, Minamimaki, Minamisaku, Nagano, 384-1805, Japan email: [email protected]
K. Nakanishi
Affiliation:
Nobeyama Radio Observatory, Minamimaki, Minamisaku, Nagano, 384-1805, Japan email: [email protected]
T. Hasegawa
Affiliation:
Gunma Astronomical Observatory, Nakayama, Takayama, Agatsuma, Gunma 377-0702
S. Matsushita
Affiliation:
Institute of Astronomy and Astrophysics, Academia Sinica, P.O.Box 23-141, Taipei 106, Taiwan, R.O.C.
K. Kohno
Affiliation:
Institute of Astronomy, University of Tokyo, 2-21-1 Osawa, Mitaka, Tokyo181-8588
R. Miura
Affiliation:
National Astronomical Observatory of Japan, 2-21-1 Osawa, Mitaka, Tokyo181-8588
Y. Tamura
Affiliation:
National Astronomical Observatory of Japan, 2-21-1 Osawa, Mitaka, Tokyo181-8588
S. K. Okumura
Affiliation:
Nobeyama Radio Observatory, Minamimaki, Minamisaku, Nagano, 384-1805, Japan email: [email protected]
R. Kawabe
Affiliation:
National Astronomical Observatory of Japan, 2-21-1 Osawa, Mitaka, Tokyo181-8588
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Abstract

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We present the high-resolution 12CO(J = 1 − 0), 13CO(J = 1 − 0) and 12CO(J = 3 − 2) maps toward a GMA located on the southern arm region of M31 using Nobeyama 45 m and ASTE 10 m telescopes. The GMA consists of two velocity-components, i.e., red and blue. The blue component shows a strong and narrow peak, whereas the red one shows a weak and broad profile. The red component has a lower 12CO(J = 1 − 0)/13CO(J = 1 − 0) ratio (~ 5) than that of the blue one (~ 16), indicating that the red component is denser than the blue one. The red component could be the decelerated gas if we consider the galactic rotational velocity in this region. We suggest that the red component is “post shock” dense gas decelerated due to a spiral density wave. This could be observational evidence of dense molecular gas formation due to galactic shock by spiral density waves.

We also present results from on-going observations toward NGC 604, which is the supergiant HII region of M33, using Nobeyama 45 m and ASTE 10 m telescopes. The ratio of 12CO(J = 3 − 2) to 12CO(J = 1 − 0) ranges from 0.3 to 1.2 in NGC 604. The 12CO(J = 1 − 0) map shows the clumpy structure while 12CO(J = 3 − 2) shows a strong peak near to the central star cluster of NGC 604. The high ratio gas is distributed on the arc-like or shell-like structure along with Hα emission and HII region detected by radio continuum. These suggest that the dense gas formation and second generation star formation occur in the surrounding gas compressed by the stellar wind and/or supernova in central star cluster.

Keywords

interstellar mediumstar formationspiral arm
Type
Contributed Papers
Information
Proceedings of the International Astronomical Union , Volume 2 , Symposium S237: Triggered Star Formation in a Turbulent ISM , August 2006 , pp. 368 - 372
Copyright
Copyright © International Astronomical Union 2007

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