Observed kinematics of the Milky Way nuclear stellar disk region

Vol. 684
5. Galactic structure, stellar clusters and populations

Observed kinematics of the Milky Way nuclear stellar disk region

Zooming into the central regions of the Milky Way unravels a great deal of structures, though often obscured by large extinction. These comprise the Galactic bulge at the kiloparsec scale, down to stellar and gaseous components with a 100 pc extent, as also seen in other galaxies. In past works, a flat, stellar disk with a 150 pc radius was discovered, it appears to cohabit with the dense molecular disk in the inner regions, and it is believed to rotate faster than its surroundings. For the present work, the authors combined the kinematics of red clump stars (to alleviate reddening issues) from the infrared APOGEE and VVV surveys to search for rotation in fields in and outside of the purported stellar disk. A rotational signal — in the sense of eastward and westward motion — of stars of different magnitudes (read, distances) of the nuclear region was indeed detected as expected. However, the team also found a kinematic structure with only one velocity direction present, which they interpret as the missing component being vignetted by the molecular zone, blocking stars behind itself. Thus there appears to be no clear signal of the nuclear stellar disk as a distinct kinematic component, which highlights the need for also a careful analysis of comparison fields, ultimately shedding more light on the mystery of the Galactic central regions.