Institution(s): 1. Kavli Institute for Astronomy and Astrophysics at Peking University, 2. Kyung Hee University
The initial mass functions (IMFs) of the Arches and Quintuplet clusters, which were formed a few million years ago in the harsh environment of the Galactic Centre (GC), have long been targets of interest to those who study the GC and the theory of star formation. The distinct star-forming conditions in the GC might have caused the clusters to have shallower slopes or elevated lower mass cutoffs in their IMFs. But their mass functions (MFs) have been revealed only down to 1-2 M⊙ (the lower limit of resolved stars), and the low-end MFs of these clusters were unknown. To estimate the unresolved part of these two GC clusters, we have devised a novel photometric method that involves the histogram of pixel intensities in the observed image, which contains information on the unresolved, faint stars. By comparing the pixel intensity histograms (PIHs) of numerous artificial images constructed from model IMFs with the observed PIH, we find that the best-fitting model IMFs for these clusters have cutoff masses less than or similar to 0.1 M⊙ and shapes not much different from that of the Kroupa MF. Our findings imply that the IMFs of the GC clusters are similar to those found in the Galactic disc.