------------------------------------------------------------------------
 gcimf_short.tex MNRAS, Okt 2009, in press
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%arXiv:0910.4960
%http://de.arxiv.org/abs/0910.4960

\documentclass[usenatbib]{mn2e}
\usepackage{graphicx,natbib}
\usepackage{amsmath,url}

\title[Stellar initial mass function in the Galactic Centre]
       {Constraining the initial mass function of stars in the Galactic Centre}

\author[U. L\"ockmann, H. Baumgardt, \& P. Kroupa]
{
   U. L\"ockmann\thanks{E-mail: uloeck@astro.uni-bonn.de (UL); holger@astro.uni-bonn.de (HB); pavel@astro.uni-bonn.de (PK)}
   , H. Baumgardt\footnotemark[1], and P. Kroupa\\
   Argelander Institute for Astronomy, University of Bonn, Auf dem H\"ugel 71, 53121 Bonn,
   Germany\\
}

\begin{document}

\date{Accepted 2009 October 20. Received 2009 September 12; in original form 2009 July 08}

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

\maketitle

\label{firstpage}

\begin{abstract}
For half a century, evidence has been growing that the formation of stars follows a universal distribution of stellar masses.
In fact, no stellar population has been found showing a systematic deviation from the canonical initial mass function (IMF)
found for example for the stars in the solar neighbourhood.
The only exception may be the young stellar discs in the Galactic Centre, which have been argued to exhibit a top-heavy IMF.

Here we discuss the question whether the extreme circumstances in the centre of the Milky Way may be the reason for a significant variation of the IMF.
By means of stellar evolution models using different codes, we show that the observed luminosity in the central parsec is too high to be 
explained by a long-standing top-heavy IMF 
as suggested by other authors, considering the limited amount of mass inferred from stellar kinematics in this region.
In contrast, continuous star formation over the Galaxy's lifetime following a canonical IMF results in a mass-to-light ratio and a 
total mass of stellar black holes (SBHs) consistent with the observations.
Furthermore, these SBHs migrate towards the centre due to dynamical friction, turning the cusp of visible stars into a core as 
observed in the Galactic Centre.  For the first time here we explain the luminosity and dynamical mass of the central cluster 
and both the presence and extent of the observed core, since the number of SBHs expected from a canonical IMF is just enough 
to make up for the missing luminous mass.

We conclude that observations of the Galactic Centre are well consistent with continuous star formation following the canonical 
IMF and do not suggest a systematic variation as a result of the region's properties such as high density, metallicity, strong tidal field etc.
If the young stellar discs prove to follow a top-heavy IMF,
the circumstances that led to their formation must be very rare, since these have not affected most of the central cluster.
\end{abstract}

\begin{keywords}
black hole physics -- stars: formation -- stars: luminosity function, mass function -- Galaxy: centre.
\end{keywords}

\end{document}