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 schoedel.tex A&A, Mar 2009, in press
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\begin{document}
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   \title{The nuclear star cluster of the Milky Way: Proper motions
     and mass \thanks{Table\,\ref{Tab:list} is
  only available in electronic form at the CDS via anonymous ftp to
  cdsarc.u-strasbg.fr (130.79.128.5) or via
    http://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/.}}

   \subtitle{}

   \author{R. Sch\"odel
          \inst{1}
          \and
          D. Merritt\inst{2}
          \and
          A. Eckart\inst{3}
          }

   \institute{Instituto de Astrof\'isica de Andaluc\'ia (IAA) - CSIC,
              Camino Bajo de Hu\'etor 50, E-18008 Granada, Spain\\
              \email{rainer@iaa.es}
         \and
             Department of Physics and Center for Computational
             Relativity and Gravitation, Rochester Institute of Technology,
             Rochester, NY 14623, USA\\
             \email{merritt@astro.rit.edu}
         \and
             I.Physikalisches Institut, Universit\"at zu K\"oln, Z\"ulpicher Str.77, 50937 K\"oln, Germany\\
             \email{eckart@ph1.uni-koeln.de}
             }

   \date{}

% \abstract{}{}{}{}{} 
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  \abstract
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{Nuclear star clusters (NSCs) are located at the photometric and
  dynamical centers of the majority of galaxies. They are among the densest
  star clusters in the Universe. The NSC in the Milky Way is the
  only object of this class that can be resolved into individual
  stars. The massive black hole Sagittarius\,A* is located at the
  dynamical center of the Milky Way NSC.}
  % aims heading (mandatory) 
{In this work we examine the proper motions of stars out to distances
  of 1.0\,pc from Sgr\,A*. The aim is to examine the velocity
  structure of the MW NSC and acquire a reliable estimate of the
  stellar mass in the central parsec of the MW NSC, in addition to the
  well-known black hole mass.}
  % methods heading (mandatory) 
{We use multi-epoch adaptive optics assisted near-infrared
  observations of the central parsec of the Galaxy obtained with
  NACO/CONICA at the ESO VLT. Stellar positions are measured via PSF
  fitting in the individual images and transformed into a common
  reference frame via suitable sets of reference stars.}
  % results heading (mandatory) 
{We measured the proper motions of
more than 6000 stars within $\sim$1.0\,pc of Sagittarius\,A*. The full
data set is provided in this work.  We largely
exclude the known early-type stars with their peculiar dynamical
properties from the dynamical analysis.  The cluster is found to
rotate parallel to Galactic rotation, while the velocity dispersion
appears isotropic {(or anisotropy may be masked by the cluster
  rotation)}. The Keplerian fall-off of the velocity dispersion due to
the point mass of Sgr\,A* is clearly detectable only at
$R\lesssim0.3$\,pc. Nonparametric isotropic and anisotropic Jeans
models are applied to the data.  They imply a best-fit black hole mass
of $3.6^{+0.2}_{-0.4}\times10^{6}$\,M$_{\odot}$. Although this value
is slightly lower than the current canonical value of
$4.0\times10^{6}$\,M$_{\odot}$, this is the first time that a proper
motion analysis provides a mass for Sagittarius\,A* that is consistent
with the mass inferred from orbits of individual stars. The point mass
of Sagittarius\,A* is not sufficient to explain the velocity data.  In
addition to the black hole, the models require the presence of an
extended mass of $0.5-1.5\times 10^{6}\,M_{\odot}$ in the central
parsec. This is the first time that the extended mass of the nuclear
star cluster is unambiguously detected. The influence of the extended
mass on the gravitational potential becomes notable at distances
$\gtrsim0.4$\,pc from Sgr\,A*. Constraints on the distribution of this
extended mass are weak. The extended mass can be explained well by the
mass of the stars that make up the cluster.}  {}

   \keywords{Galaxy: center --
                Galaxy: nucleus --
              Galaxy: structure
               }

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