Massive Young Stars in the Galactic Center

TL;DR

This study presents detailed observations of the nuclear star cluster in the Galactic Center, revealing two warped eccentric disks of young massive stars, a top-heavy initial mass function in the disks, and a puzzling lack of late-type stars in the core.

Contribution

It provides the first comprehensive analysis of the stellar populations and their spatial distributions in the Galactic Center using integral field spectroscopy.

Findings

Most young massive stars are in two eccentric disks around SgrA*.

The disk stars have a top-heavy initial mass function.

A dearth of late-type stars is observed in the central region.

Abstract

We summarize our latest observations of the nuclear star cluster in the central parsec of the Galaxy with the adaptive optics assisted, integral field spectrograph SINFONI on the ESO/VLT, which result in a total sample of 177 bona fide early-type stars. We find that most of these Wolf Rayet (WR), O- and B- stars reside in two strongly warped eccentric (<e> = 0.36+/-0.06) disks between 0.8" and 12" from SgrA*, as well as a central compact concentration (the S-star cluster) centered on SgrA*. The later type B stars (mK>15) in the radial interval between 0.8" and 12" seem to be in a more isotropic distribution outside the disks. We observe a dearth of late-type stars in the central few arcseconds, which is puzzling. The stellar mass function of the disk stars is extremely top-heavy with a best fit power law of dN/dm~m^(-0.45+/-0.3). Since at least the WR/O-stars were formed in situ in a single star formation event ~6 Myrs ago, this mass function probably reflects the initial mass function (IMF). The mass functions of the S-stars inside 0.8" and of the early-type stars at distances beyond 12" differ significantly from the disk IMF; they are compatible with a standard Salpeter/Kroupa IMF (best fit power law of dN/dm~m^(-2.15+/-0.3).