We present 12CO (2-1) observations towards the central region <br />
of the Seyfert 2 galaxy NGC~4258 with the Submillimeter Array <br />
(SMA). Our interferometric maps show two arm-like elongated <br />
components along the major axis of the galaxy, with no strong <br />
nuclear concentration. The CO (2-1) morphology and kinematics <br />
are similar to previous CO (1-0) results. The velocity field of the <br />
components agrees with the general galactic rotation, except for <br />
the east elongated component, which shows a significant velocity <br />
gradient along the east-west direction. In order to account for the <br />
velocity field, the warped rotating disk is necessary. We propose <br />
the kinematical models where the warped rotating disk is also <br />
expanding. The line ratio of CO(2-1)/CO(1-0) reveals that the <br />
eastern component with the anomalous velocity gradient appears <br />
to be warmer and denser. This is consistent with the gas in this <br />
component being closer to the center, being heated by the central <br />
engine, and possibly excited by expanding motions from the nuclear <br />
region.<br />