The Spatial Evolution of Stellar Structures in the LMC

TL;DR

This study investigates how stellar structures in the Large Magellanic Cloud form and evolve, revealing that stars start with fractal substructure and become more uniform within approximately 175 million years, driven by galactic crossing times.

Contribution

It provides the first detailed analysis of the spatial evolution of stellar populations in the LMC, demonstrating the timescale and processes of structural homogenization.

Findings

Stars in the LMC are born with fractal substructure (~1.8 dimension).

Stellar structures evolve towards uniformity within ~175 Myr.

Infant cluster mortality has negligible impact on galactic structure.

Abstract

We present an analysis of the spatial distribution of various stellar populations within the Large Magellanic Cloud. We combine mid-infrared selected young stellar objects, optically selected samples with mean ages between ~9 and ~1000 Myr, and existing stellar cluster catalogues to investigate how stellar structures form and evolve within the LMC. For the analysis we use Fractured Minimum Spanning Trees, the statistical Q parameter, and the two-point correlation function. Restricting our analysis to young massive (OB) stars we confirm our results obtained for M33, namely that the luminosity function of the groups is well described by a power-law with index -2, and that there is no characteristic length-scale of star-forming regions. We find that stars in the LMC are born with a large amount of substructure, consistent with a 2D fractal distribution with dimension ~1.8 and evolve towards a uniform distribution on a timescale of ~175 Myr. This is comparable to the crossing time of the galaxy and we suggest that stellar structure, regardless of spatial scale, will be eliminated in a crossing time. This may explain the smooth distribution of stars in massive/dense young clusters in the Galaxy, while other, less massive, clusters still display large amounts of structure at similar ages. By comparing the stellar and star cluster distributions and evolving timescales, we show that infant mortality of clusters (or 'popping clusters') have a negligible influence on galactic structure. Finally, we quantify the influence of the elongation, differential extinction, and contamination of a population on the measured Q value.