M51的自转曲线反常和银河弯曲
Rotation Curve Anomaly and Galactic Warp in M51
摘要：
我们重新审视了近面对面星系M51的自转曲线异常，它显示了外盘自转速度的下降明显快于开普勒定律，进一步显示了最外面的HI盘明显的反向旋转。我们解释这种异常是由于银盘的翘曲，并确定了翘曲结构的M51的磁盘使用倾斜环的方法，假设的内禀旋转曲线是正常的。它表明，在一个恒定的倾角，磁盘是近平的内部磁盘，但磁盘突然弯曲半径为7.5千秒差距约27 $°$。然后，倾斜角单调向外减小，在18 kpc处达到完美的正面环，超过该环，盘在与内盘相反的方向上弯曲，导致明显的反向旋转。
英文摘要：
We revisit the anomaly of rotation curve in the nearly face-on galaxy M51 that shows an apparently faster decrease of rotation velocity than the Keplerian law in the outer disk, further showing apparent counter rotation in the outermost HI disk. We interpret this anomaly as due to warping of the galactic disk, and determined the warping structure of M51's disk using the tilted-ring method, assuming that the intrinsic rotation curve is normal. It is shown that the disk is nearly flat in the inner disk at a constant inclination angle, but the disk suddenly bends at radius 7.5 kpc by about 27$°$. The inclination angle, then, decreases monotonically outward reaching a perfect face-on ring at 18 kpc, beyond which the disk is warped in the opposite sense to the inner disk, resulting in apparent counter rotation.
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