Mira variable cand. in Milky Way NSD region

Weak evidence for inside-out growth and both radial and vertical dynamical heating with time of the nuclear stellar disc is presented suggesting the nuclear stellar disc is dynamically well-mixed. Furthermore, for Mira variables around a ~350 day period, there is a clear transition from nuclear stellar disc-dominated kinematics to background bar-bulge-dominated kinematics. Using a Mira variable period--age relation calibrated in the solar neighbourhood, this suggests the nuclear stellar disc formed in a significant burst in star formation (8+/-1)Gyr ago, although the data are also weakly consistent with a more gradual formation of the nuclear stellar disc at even earlier epochs.

This implies a relatively early formation time for the Milky Way bar (>~8Gyr), which has implications for the growth and state of the young Milky Way and its subsequent history.