THE NUCLEAR CLUSTER OF THE MILKY WAY: TOTAL MASS AND LUMINOSITY

Abstract

We obtain the basic properties of the nuclear cluster of the Milky Way. First, we investigate the structural properties by constructing a stellar density map of the central 1000 '' using extinction-corrected old star counts from VISTA, WFC3/IR, and VLT/NACO data. We describe the data using two components. The inner, slightly flattened (axis ratio of q = 0.80 +/- 0.04) component is the nuclear cluster, while the outer component corresponds to the stellar component of the circumnuclear zone. For the nuclear cluster, we measure a half-light radius of 178 +/- 51 '' approximate to 7 +/- 2 pc and a luminosity of M-Ks = -16.0 +/- 0.5. Second, we measure detailed dynamics out to 4 pc. We obtain 10,351 proper motions from AO data, and 2513 radial velocities from VLT/SINFONI data. We determine the cluster mass by means of isotropic spherical Jeans modeling. We fix the distance to the Galactic Center and the mass of the supermassive black hole. We model the cluster either with a constant M/L or with a power law. For the latter case, we obtain a slope of 1.18 +/- 0.06. We get a cluster mass within 100. of M-100 '' = (6.09 +/- 0.53 vertical bar(fixR0) +/- 97 vertical bar R-0) x 10(6)M(circle dot) for both modeling approaches. A model which includes the observed flattening gives a 47% larger mass (see Chatzopoulos et al.). Our results slightly favor a core over a cusp in the mass profile. By minimizing the number of unbound stars within 8 '', we obtain a distance of R-0 = 8.53(-0.15)(+0.21) kpc when using an R-0 supermassive black hole mass relation from stellar orbits. Combining our results, we obtain M/L= 0.51 +/- 0.12M(circle dot)/L-circle dot, K-s, which is roughly consistent with a Chabrier IMF.