Photometry and proper motion cat. in NSD region

We find that the main difference between the Nuclear Stellar Disk region and its surroundings is that at the former we see only stars moving eastwards, that we believe are located in front of the Galactic Center. On the contrary, in every other direction, we see the brightest Red Clump stars moving eastwards, and the faintest ones moving westwards, as expected for a rotating disk. We interpret this observations as produced by the Central Molecular Zone, hiding stars behind itself.

What we observe is compatible with being produced just by the absence of the component at the back, without requiring the presence of a cold, fast rotating disk. This component is also not clearly detected in the newest release of the APOGEE catalogue. In other words, we find no clear signature of the Nuclear Stellar Disk as a distinct kinematical component.

This work highlights the need for nearby control fields when attempting to characterize the properties of the Nuclear Stellar Disk, as the different systematics affecting this region, compared to nearby ones, might introduce spurious results. Deep, wide field and high resolution photometry of the inner 4 degrees of the Milky Way is needed, in order to understand the structure and kinematics of this very unique region of our Galaxy.