Structure and Kinematics of COJ= 2–1 Emission in the Central Region of NGC 4258

We present 12CO (J=2-1) observations towards the central region of theSeyfert 2 galaxy NGC 4258 with the Submillimeter Array (SMA). Ourinterferometric maps show two arm-like elongated components along the majoraxis of the galaxy, with no strong nuclear concentration. The CO (2-1)morphology and kinematics are similar to previous CO (1-0) results. Thevelocity field of the components agrees with the general galactic rotation,except for the east elongated component, which shows a significant velocitygradient along the east-west direction. In order to account for the velocityfield, we propose the kinematical model where the warped rotating disk is alsoexpanding. The line ratio of CO(2-1)/CO(1-0) reveals that the eastern componentwith the anomalous velocity gradient appears to be warmer and denser. This isconsistent with the gas in this component being closer to the center, beingheated by the central activities, and possibly interacted by expanding motionsfrom the nuclear region.Comment: accepted for publication in ApJ, 21 pages, 8 figure