银河系薄盘形成对核球的动力学影响

The Dynamic Influence of Thin Disk Formation on the Galactic Bulge

近期的研究认为,银河系核球是侧面看到的棒,由原初盘演化而来,并非由星系并合形成。核球形成的时间在银河系演化早期,而后续来自晕的气体吸积在银河系薄盘处形成的新恒星对核球是否会造成比较大的动力学影响,仍是一个重要的问题。通过在盘上添加新粒子的方法模拟薄盘的形成,发现在大多数情况下薄盘形成并没有对核球的平均速度、速度弥散、棒的强度和旋转速度产生明显的影响;但是在恒星形成率特别大或者新形成的恒星特别接近棒的时候,核球区的恒星速度弥散、棒的强度和旋转速度会同时增大。薄盘恒星在加入1~2 Ga后,在经度3°~10°处其视向速度分布有可能存在类似APOGEE巡天中观测到的高速峰。高速峰的形成时间与恒星添加位置有关,添加位置离棒越近,高速峰越早形成。

Recent studies suggest that the Milky Way bulge is mostly the Milky Way bar viewed nearly end-on, which formed out of a primordial disk without major mergers. The bulge formed in the early time of the galaxy evolution, so whether the Galactic thin disk forming from the cooled halo gas will have a great dynamical influence on the bulge is still an important question. Our model mimicks the star formation of Galactic thin disk by adding new particles in the disk plane. We find that the thin disk formation does not have a significant dynamical influence on the bulge, unless the star formation rate is very large or new stars are initially placed too close to the bar. After thin disk stars have been added for 1 ~2 Ga, the line-of-sight velocity(Vlos) distribution shows a high |Vlos| peak in longitudes between 3° and 10°, which might help to explain the high |Vlos| peak observed in the APOGEE survey. The forming time of the high |Vlos| peak is related to the position of newly-formed stars. If stars are added closer to the bar, they are easier to be trapped by the bar and the high |Vlos| peak appears earlier.