The stellar population and mass distribution at the galactic center

Abstract

We have imaged the 2.3µm v=2-0 CO bandhead at the Galactic Center using a Fabry-Perot spectrometer coupled to an infrared camera (IRCAM) at the 3.8-m UK Infrared Telescope. Our observations cover 1.5x1.5 pc of the Galactic Center centered on the IRS16/SgrA* complex. From our data, we have derived maps of the (1) CO index, (2) velocity dispersion, and (3) rotational velocities for both the faint diffuse and individual stars in the region. The CO absorption declines from ~ 35% at ≥ 1 pc from IRS16/SgrA* to ~ few percent at the very center, which may be due to a change in stellar population, destruction of the photospheric CO in the late-type giants at the Galactic Center, or contamination of the CO absorption by some source such as continuum dust emission or CO in emission filling in the absorption. Collisional stripping of the giant stars primarily responsible for the CO absorption seems a likely explanation for the decline in CO strength with projected radius from IRS16. The velocity dispersion of the diffuse light, consistent with that of the individual stars but not with published gas velocities, peaks at ~150 km/s at the center and declines to ~100 km/s at a projected radius of ~ 1 pc. The stellar rotation curve, also inconsistent with the gas measurements, has an amplitude of roughly 75 km/s and is slightly skewed in the sense of higher velocities to the NE of center. Implications for the mass distribution are discussed. The presence of a supermassive black hole at the Galactic Center cannot be confirmed with this data, although if the stellar cluster follows an r-1.8 density power law then the kinematic data presented here supports previous claims of a large mass concentration at the Galactic Center.