SMA CO(3-2) Observation of the Seyfert 2 Galaxy M51

摘要

We have obtained the first interferometric CO(3-2) image (3'!9 x1'!6 or 160 pc x 65 pc) of the central~36" region of the Seyfert 2 galaxy M51with the Submillimeter Array (SMA). The CO(3-2) emission is strongly peakedat the nucleus and is weakly distributed along the spiral arm to the northwest.The CO(3-2) integrated intensity of the central peak is almost twice as highas that in CO(1-0), indicating that the circumnuclear molecular gas is warmand dense. Similar intensity ratios are seen in shocked regions in our Galaxy,suggesting that the properties of the gas in M51 may be related to AGN or star-burst activity. The circumnuclear molecular gas shows a linear velocity gradientalong the radio continuum jet, in addition to the gradient perpendicular to it.The velocity gradient along the jet can also be explained by AGN or starburstactivity, which is consistent with the high intensity ratio.