Characteristic Scales in Stellar Clustering: A Transition Near the Disk Scale Height

TL;DR

This study uses autocorrelation functions to identify characteristic scales in the clustering of young stars across different galaxies, revealing a transition near the disk scale height that indicates the influence of galaxy structure on stellar distribution.

Contribution

It introduces an objective autocorrelation method to detect characteristic clustering scales in stellar populations across multiple galaxies, highlighting a transition related to disk geometry.

Findings

Transition to weaker clustering at ~1 kpc in LMC and M31, and at 300 pc in M33.

On smaller scales, clustering is scale-free over two orders of magnitude.

Correlation dimension varies from 1.0 in M31 to 1.8 in SMC.

Abstract

The autocorrelation function provides an objective test for the existence of special scales in the hierarchical clustering of young stars. We apply this measure to single-star photometry for the brightest main sequence stars in the Small Magellanic Cloud (SMC), the Large Magellanic Cloud (LMC), M33, and M31, using data from the Magellanic Clouds Photometric Survey and the Massey Local Group Survey. Our primary result is the identification of a transition to a higher correlation dimension (weaker clustering) at one kpc in the LMC and M31, and at 300 pc in M33. We suggest that this transition marks the large-scale regime where disk geometry and dynamics set the scale for structure. On smaller scales, the correlation functions for each galaxy are scale-free over at least two orders of magnitude, with a projected correlation dimension varying from 1.0 for M31 to 1.8 for the SMC. This variation is probably caused by a combination of differences in stellar ages and masses, physical environment, and extinction.