||Clusters Near the Center of the Galaxy - How Weird is Their IMF?
||440, UP2010: Have Observations Revealed a Variable Upper End of the Initial Mass Function?
||It has been argued on theoretical grounds that the initial mass function (IMF) in
the hot, UV-rich Galactic center environment might be biased to
high-mass stars. Over the past decade, several attempts were made
to derive the stellar mass function in the young, massive Arches cluster
near the Galactic center, as well as in the nuclear cluster itself.
While there is indirect evidence for a top-heavy IMF
in the young and old population in the nuclear cluster in the immediate
vicinity of the supermassive black hole,
the direct observations of the MF are subject to large uncertainties,
such as field contamination, age and distance estimation, varying extinction
along the line of sight towards the center of the Galaxy, and cluster membership.
Progressing from the observed present-day stellar mass distribution
to conclusions on the initial stellar mass function is particularly difficult
in the Galactic center environment, where clusters are rapidly disrupted by
the strong tidal field in the inner bulge.
Here, the evidence for a top-heavy IMF in the young nuclear cluster
is briefly summarised, and the different observational studies of the Arches
cluster are compared. The major focus, however, is placed on the discussion
of the biases still inherent to present-day MF derivations, both along the
Galactic center line of sight and in dense, young clusters in general.
The effects of spatially varying extinction, non-radially symmetric
incompleteness in high-density environments, and membership selection
are addressed. The spatial area within which the present-day MF can reliably
be derived in young, massive clusters is frequently restricted by the field star
density, and hence does not need to cover even a major fraction of the
complete cluster. Biases arising from these selection effects are analysed.
Finally, proper motion studies with precision astrometry employing adaptive
optics systems from the ground are suggested as a solution to the membership
problem, and the Arches cluster is chosen as an example to display the advantages
of this approach.