The young stars in the Galactic Center

TL;DR

This study conducts a comprehensive spectroscopic survey of over 2800 stars in the Galactic Center, identifying 195 young stars and analyzing their angular momentum distribution to reveal complex structures like warped disks and overdensities.

Contribution

It introduces an isotropic cluster prior for angular momentum analysis and extends the catalog of young stars, providing new insights into their spatial and kinematic structures.

Findings

Identification of 195 young stars, 79 more than previously known.

Detection of a warped clockwise disk with a changing angular momentum profile.

Discovery of two new overdensities of angular momentum at large separations.

Abstract

We present a large ${\sim 30" \times 30"}$ spectroscopic survey of the Galactic Center using the SINFONI IFU at the VLT. Combining observations of the last two decades we compile spectra of over $2800$ stars. Using the Bracket-$\gamma$ absorption lines we identify $195$ young stars, extending the list of known young stars by $79$. In order to explore the angular momentum distribution of the young stars, we introduce an isotropic cluster prior. This prior reproduces an isotropic cluster in a mathematically exact way, which we test through numerical simulations. We calculate the posterior angular momentum space as function of projected separation from Sgr~A*. We find that the observed young star distribution is substantially different from an isotropic cluster. We identify the previously reported feature of the clockwise disk and find that its angular momentum changes as function of separation from the black hole, and thus confirm a warp of the clockwise disk ($p \sim 99.2\%$). At large separations, we discover three prominent overdensities of angular momentum. One overdensity has been reported previously, the counter-clockwise disk. The other two are new. Determining the likely members of these structures, we find that as many as $75\%$ of stars can be associated with one of these features. Stars belonging to the warped clockwise-disk show a top heavy K-band luminosity function, while stars belonging to the larger separation features do not. Our observations are in good agreement with the predictions of simulations of in-situ star formation, and argue for common formation of these structures.