Hierarchical structures in the Large and Small Magellanic Clouds

TL;DR

This study examines the spatial correlation of structures in the Magellanic Clouds, revealing hierarchical star formation patterns and differences in clustering based on age and size.

Contribution

It provides new insights into the hierarchical organization and evolution of stellar structures in the Magellanic Clouds based on size, age, and spatial correlation analysis.

Findings

Young clusters are highly spatially correlated and associated with star-forming regions.

Old clusters show extensive mixing and lack of spatial correlation.

Small structures are spatially self-correlated, large ones are not.

Abstract

We investigate the degree of spatial correlation among extended structures in the LMC and SMC. To this purpose we work with sub-samples characterised by different properties such as age and size, taken from the updated catalogue of Bica et al. or gathered in the present work. The structures are classified as star clusters or non-clusters (basically, nebular complexes and their stellar associations). The radius distribution functions follow power-laws ($dN/dR\propto R^{-\alpha}$) with slopes and maximum radius ($R_{max}$) that depend on object class (and age). Non-clusters are characterised by $\alpha\approx1.9$ and $R_{max}\la472$ pc, while young clusters (age $\la10$ Myr) have $\alpha\approx3.6$ and $R_{max}\la15$ pc, and old ones (age $\ga600$ Myr) have $\alpha\approx2.5$ and $R_{max}\la40$ pc. Young clusters present a high degree of spatial self-correlation and, especially, correlate with star-forming structures, which does not occur with the old ones. This is consistent with the old clusters having been heavily mixed up, since their ages correspond to several LMC and SMC crossing times. On the other hand, with ages corresponding to fractions of the respective crossing times, the young clusters still trace most of their birthplace structural pattern. Also, small clusters ($R<10$ pc), as well as small non-clusters ($R<100$ pc), are spatially self-correlated, while their large counterparts of both classes are not. The above results are consistent with a hierarchical star-formation scenario for the LMC and SMC.