SMA 12 CO ( J = 3 – 2 ) interferometric observations of the central region of M 51

We present the first interferometric CO(J = 3 – 2) observations (beam size of 3. 9 × 1. 6 or 160 pc × 65 pc) with the Submillimeter Array (SMA) toward the center of the Seyfert 2 galaxy M51. The image shows a strong concentration at the nucleus and weak emission from the spiral arm to the northwest. The integrated intensity of the central component in CO(J = 3 – 2) is almost twice as high as that in CO(J = 1 – 0), indicating that the molecular gas within an ∼ 80 pc radius of the nucleus is warm (& 100 K) and dense (∼ 10 cm). Similar intensity ratios are seen in shocked regions in our Galaxy, suggesting that these gas properties may be related to AGN or starburst activity. The central component shows a linear velocity gradient (∼ 1.4 km s pc) perpendicular to the radio continuum jet, similar to that seen in previous observations and interpreted as a circumnuclear molecular disk/torus around the Seyfert 2 nucleus. In addition, we identify a linear velocity gradient (0.7 km s pc) along the jet. Academia Sinica Institute of Astronomy and Astrophysics, P.O. Box 23-141, Taipei 106, Taiwan, R.O.C.; [email protected] Harvard-Smithsonian Center for Astrophysics, 60 Garden St., MS-78, Cambridge, MA 02138 Department of Physics, National Taiwan Normal University, 88 Sec. 4, Ting-Chou Road, Taipei 116, Taiwan, R.O.C. Purple Mountain Observatory, Chinese Academy of Sciences, Nanjing 210 008, P.R. China University of Massachusetts, Department of Astronomy, Amherst, MA 01003 1. Physikalisches Institut, Universität zu Köln, 50937 Köln, Germany