The distribution of stars around the Milky Way's central black hole II: Diffuse light from sub-giants and dwarfs

Schödel, R.; Gallego-Cano, E.; Dong, H.; Nogueras-Lara, F.; Gallego-Calvente, A. T.; Amaro-Seoane, P.; Baumgardt, H.

January, 2018

This is the second of three papers that search for the predicted stellar cusp around the Milky Way's central black hole, Sagittarius A*, with new data and methods.We use adaptive optics assisted high angular resolution images obtained with the NACO instrument at the ESO VLT. Through optimised PSF fitting we remove the light from all detected stars above a given magnitude limit. Subsequently we analyse the remaining, diffuse light density. The azimuthally averaged surface light density profile within a projected distance of R0.5 pc from Sagittarius A* can be described consistently by a single power law with an exponent of Gamma=0.28+-0.03, similar to what has been found for the surface number density of faint stars in Paper I. The analysed diffuse light arises from sub-giant and main-sequence stars with K=19-20 with masses of 1-2 Msol. These stars can be old enough to be dynamically relaxed. The observed power-law profile and its slope are consistent with the existence of a relaxed stellar cusp around the Milky Way's central black hole. We find that a Nuker law provides an adequate description of the nuclear cluster's intrinsic shape (assuming spherical symmetry). The 3D power-law slope near SgrA* is gamma=1.23+-0.05. The stellar density decreases more steeply beyond a break radius of about 3 pc, which corresponds roughly to the radius of influence of the massive black hole. At a distance of 0.01 pc from the black hole, we estimate a stellar mass density of 2.3+-0.3x1e7 Msol pc(-3) and a total enclosed stellar mass of 180+-20 Msol.