------------------------------------------------------------------------
 gcdn.tex MNRAS, 394, 1841-1846, 2009
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%astro-ph/0901.1660
%http://www3.interscience.wiley.com/cgi-bin/fulltext/122245841/HTMLSTART

\documentclass[usenatbib]{mn2e}


\title{On the number of young stellar discs in the Galactic Centre}

\author{Ulf L\"ockmann and Holger Baumgardt}



\begin{document}

\date{Accepted 2009 January 8.  Received 2009 January 6; in original
form 2008 June 16}

\pagerange{\pageref{firstpage}--\pageref{lastpage}} \pubyear{2009}


\maketitle

\label{firstpage}

\begin{abstract}
Observations of the Galactic Centre show evidence of disc-like
structures of very young stars orbiting the central super-massive black
hole within a distance of a few 0.1 pc.
While it is widely accepted that about half of the stars form a
relatively flat disc rotating clockwise on the sky,
there is a substantial ongoing debate on whether there is a second,
counter-clockwise disc of stars.

By means of N-body simulations using our BHINT code, we show that two
highly inclined stellar discs with the observed properties cannot be
recognised as two flat circular discs after 5 Myr of mutual interaction.
Instead, our calculations predict a significant warping of the two
discs, which we show to be apparent among the structures observed in the
Galactic Centre. While the high eccentricities of the observed
counter-clockwise orbits suggest an eccentric origin of this system, we
show the eccentricity distribution in the inner part of the more massive
clockwise disc to be perfectly consistent with an initially circular
disc in which stellar eccentricities increase due to both non-resonant
and resonant relaxation.

We conclude that the relevant question to ask is therefore not whether
there <i>are</i> two discs of young stars, but whether there <i>were</i>
two such discs to begin with.

\end{abstract}


\begin{keywords}
black hole physics -- stellar dynamics -- methods: $N$-body simulations
-- Galaxy: centre.
\end{keywords}

\end{document}