Dynamics of Stars in the Inner Galactic Bulge Revealed from SiO Maser Surveys

We surveyed ~300 MSX/2MASS infrared objects in the 7° × 2° area of the Galactic center in the ~43 GHz SiO maser lines, obtaining accurate radial velocities of ~160 detected objects. The longitude–velocity diagram of these objects reveals two conspicuous features: one indicating a linear velocity increase with longitude with |l| < 1.5°, which is likely to be associated with the inner bar, and the other having eccentric velocities with |V _lsr| >250 km s^-1. Based on numerical simulations of stellar orbits in the Galactic bulge, we conclude that the latter feature is created as a result of a past star formation in the bulge, when the intersecting point of the x ₁ and x ₂ orbits was considerably outside of the present position.