The Arches cluster - evidence for a truncated MF in the GC?

Abstract

The Arches cluster serves as an indicator for star formation and cluster evolution in the dense GC environment. A high-resolution adaptive optics study of the starburst suggests a present-day mass function (MF) that deviates significantly from the standard IMF in the intermediate-mass regime. A turn-over is observed around 6 - 7 M⊙, below which the MF appears to decline. Above ∼ 10 M⊙, the integrated MF in the cluster center, r < 0.4 pc, displays a moderately flattened slope of Γ = −0.9±0.15, close to the Orion IMF with Γ = −1.1 [8]. In particular in the cluster core, r < 0.2 pc, a pronounced peak is visible at 7 M⊙, while a weaker change in the MF slope is found in the annulus, 0.2 < r < 0.4 pc. We compare the Arches cluster to the starburst cluster NGC 3603 in the Carina spiral arm, which displays a moderately flattened present-day MF with Γ = −0.9 all the way down to subsolar masses. The deviation in the Arches MF can be caused by accelerated dynamical evolution due to tidal disruption of the cluster in the GC potential, or can be the cause of a deviating intial mass function in the Galactic Center. Theoretical arguments for a potentially deviating IMF in a dense environment are recalled.