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 ms.tex ApJ, November 2008, in press
Date: Tue, 22 Jul 2008 15:16:36 -0400
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%arXiv:0807.3044
%http://xxx.lanl.gov/pdf/0807.3044v1

\documentclass[12pt,preprint]{aastex}

\shorttitle{The Rotating Nuclear Star Cluster in NGC~4244}
\shortauthors{Seth et al.}

\begin{document}

%\slugcomment{Draft, last update \today}
\slugcomment{Resubmitted Version 2, July 14, 2008}


\title{The Rotating Nuclear Star Cluster in NGC~4244}

\author{Anil C. Seth\altaffilmark{1,2}, Robert D. Blum\altaffilmark 
{3}, Nate Bastian \altaffilmark{4}, Nelson Caldwell\altaffilmark{1},  
Victor P. Debattista\altaffilmark{5}}
Garden Street Cambridge, MA 02138}
\altaffiltext{2}{Center for Astrophysics Fellow, {\tt  
aseth@cfa.harvard.edu}}
\altaffiltext{3}{National Optical Astronomy Observatory, 950 North  
Cherry Avenue, Tucson, AZ, 85721}
\altaffiltext{4}{Institute of Astronomy, University of Cambridge}
\altaffiltext{5}{Centre For Astrophysics, University of Central  
Lancashire, Preston PR1 2HE, UK, {\it RCUK Fellow}}


We present observations of the nuclear star cluster in the nearby
edge-on spiral galaxy NGC~4244 using the Gemini Near-Infrared Integral
Field Spectrograph (NIFS) with laser guide star adaptive optics.  From
a previous study of edge-on galaxies, this nuclear star cluster was
found to be one of a sample of clusters that appear flattened along
the plane of their host galaxies disks.  Such clusters show evidence
for multiple morphological components, with younger/bluer disk
components and older/redder spheroidal components.  Our new
observations of NGC~4244 show clear rotation of 30 km\,s$^{-1}$ within
the central 10~pc (0.5$\arcsec$) of the cluster.  The central velocity
dispersion is found to be 28$\pm$2 km\,s$^{-1}$.  The multiple stellar
populations inferred from the optical colors and spectra are seen as
variations in the CO line strength in the NIFS spectra.  The rotation
is clearly detected even in the older, more spheroidal stellar
component.  We discuss evidence for similar structures and kinematics
in the nuclear star clusters of other galaxies including M33 and the
Milky Way.  Our observations support two possible formation
mechanisms: (1) episodic accretion of gas from the disk directly onto
the nuclear star cluster, or (2) episodic accretion of young star
clusters formed in the central part of the galaxy due to dynamical
friction.

\end{abstract}

\keywords{galaxies:nuclei -- galaxies:star clusters -- galaxies:
spiral -- galaxies: kinematics and dynamics -- galaxies:formation --
galaxies: individual (NGC~4244) }