HST Palpha Survey of the Galactic Center -- Searching the missing young stellar populations within the Galactic Center

TL;DR

This HST Paα survey of the Galactic Center provides a more complete inventory of massive stars, revealing new structures and recent star formation activity, including previously unknown regions and a significant population of evolved stars.

Contribution

The survey offers the first detailed mapping of Paα emission in the Galactic Center, identifying new stellar populations, structures, and evidence of recent star formation not seen in prior studies.

Findings

157 Paα emitting sources identified, half outside known clusters

Discovery of new extended structures like bow shocks and H II regions

Evidence of star formation activity around 350 Myr ago

Abstract

We present preliminary results of our \hst Pa$\alpha$ survey of the Galactic Center (\gc), which maps the central 0.65$\times$0.25 degrees around Sgr A*. This survey provides us with a more complete inventory of massive stars within the \gc, compared to previous observations. We find 157 Pa$\alpha$ 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 Pa$\alpha$ 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 Pa$\alpha$ diffuse emission and tens of Pa$\alpha$ emitting sources in the negative Galactic longitude suggesting recent star formation activities, which were not known previously. Furthermore, in our survey, we detect $\sim$0.6 million stars, most of which are red giants or AGB stars. Comparisons of the magnitude distribution in 1.90 $\mu$m 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 .