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arXiv · 0906.4894

Density and kinematic cusps in M54 at the heart of the Sagittarius dwarf galaxy: evidence for a 10^4 M_sun Black Hole?

R. Ibata·M. Bellazzini·S. C. Chapman·E. Dalessandro·F. R. Ferraro·M. Irwin·B. Lanzoni·G. F. Lewis·A. D. Mackey·P. Miocchi·A. Varghese
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Abstract

We report the detection of a stellar density cusp and a velocity dispersion increase in the center of the globular cluster M54, located at the center of the Sagittarius dwarf galaxy (Sgr). The central line of sight velocity dispersion is 20.2 +/- 0.7 km/s, decreasing to 16.4 +/- 0.4 km/s at 2.5" (0.3 pc). Modeling the kinematics and surface density profiles as the sum of a King model and a point-mass yields a black hole (BH) mass of ~ 9400 M_sun. However, the observations can alternatively be explained if the cusp stars possess moderate radial anisotropy. A Jeans analysis of the Sgr nucleus reveals a strong tangential anisotropy, probably a relic from the formation of the system.

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R. Ibata, M. Bellazzini, S. C. Chapman, E. Dalessandro, F. R. Ferraro, M. Irwin, B. Lanzoni, G. F. Lewis, A. D. Mackey, P. Miocchi, A. Varghese. 2009-06-26. Density and kinematic cusps in M54 at the heart of the Sagittarius dwarf galaxy: evidence for a 10^4 M_sun Black Hole?. https://doi.org/10.1088/0004-637x%2F699%2F2%2Fl169

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