The HI Velocity Field and Rotation Curve of M81

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Session 66 -- Spiral Galaxies
Oral presentation, Thursday, January 13, 2:15-3:45, Salon VI Room (Crystal Gateway)

[66.04] The HI Velocity Field and Rotation Curve of M81

D.J. Westpfahl (NMIMT), D.S. Adler (NRAO-VLA)

We present an initial analysis of the HI velocity field of M81 as revealed by new observations with the VLA in the B, C, and D configurations using velocity channels of 2.6 km s$^{-1}$. The resulting map shows the HI velocity to an accuracy of better than 1 km s$^{-1}$ in each pixel. Streaming motions of order 40 km s$^{-1}$ are easily seen in the arms, the pattern of streaming in the northeast arm is kinked, consistent with density-wave models, the pattern in the southeast arm is not. The rotation curve turns over on both sides, the turnover is stronger on the approaching side than the receeding side. The turnover suggests a large ratio of luminous to dark matter in M81.

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