HST Pa Survey of the Galactic Center – Searching the missing young stellar populations within the Galactic Center

We present preliminary results of our HST Paα survey of the Galactic Center (GC), which maps the central 0.65×0.25 degrees around Sgr A*. This survey provides us with a more complete inventory of massive stars within the GC, compared to previous observations. We find 157 Paα emitting sources, which are evolved massive stars. Half of them are located outside of three young massive star clusters near Sgr A*. The loosely spatial distribution of these field sources suggests that they are within less massive star clusters/groups, compared to the three massive ones. Our Paα mosaic not only resolves previously well-known large-scale filaments into fine structures, but also reveals many new extended objects, such as bow shocks and H II regions. In particular, we find two regions with large-scale Paα diffuse emission and tens of Paα emitting sources in the negative Galactic longitude suggesting recent star formation activities, which were not known previously. Furthermore, in our survey, we detect ∼0.6 million stars, most of which are red giants or AGB stars. Comparisons of the magnitude distribution in 1.90 μm and those from the stellar evolutionary tracks with different star formation histories suggest an episode of star formation process about 350 Myr ago in the GC.