The VMC Survey XXVII. Young Stellar Structures in the LMC$'$s Bar Star-Forming Complex

TL;DR

This study investigates the hierarchical organization and evolution of young stellar structures in the LMC's bar region, revealing their power-law distributions, turbulence regulation, and dispersal timescale of about 100 million years.

Contribution

It provides a detailed analysis of the hierarchical and temporal evolution of young stellar structures in the LMC's bar, highlighting their power-law distributions and dispersal timescale.

Findings

Young stellar structures follow power-law size and mass distributions.

Structures become less substructured with increasing age, dispersing by ~100 Myr.

Hierarchical organization supports turbulence-regulated star formation.

Abstract

Star formation is a hierarchical process, forming young stellar structures of star clusters, associations, and complexes over a wide scale range. The star-forming complex in the bar region of the Large Magellanic Cloud is investigated with upper main-sequence stars observed by the VISTA Survey of the Magellanic Clouds. The upper main-sequence stars exhibit highly non-uniform distributions. Young stellar structures inside the complex are identified from the stellar density map as density enhancements of different significance levels. We find that these structures are hierarchically organized such that larger, lower-density structures contain one or several smaller, higher-density ones. They follow power-law size and mass distributions as well as a lognormal surface density distribution. All these results support a scenario of hierarchical star formation regulated by turbulence. The temporal evolution of young stellar structures is explored by using subsamples of upper main-sequence stars with different magnitude and age ranges. While the youngest subsample, with a median age of log($\tau$/yr)~=~7.2, contains most substructure, progressively older ones are less and less substructured. The oldest subsample, with a median age of log($\tau$/yr)~=~8.0, is almost indistinguishable from a uniform distribution on spatial scales of 30--300~pc, suggesting that the young stellar structures are completely dispersed on a timescale of $\sim$100~Myr. These results are consistent with the characteristics of the 30~Doradus complex and the entire Large Magellanic Cloud, suggesting no significant environmental effects. We further point out that the fractal dimension may be method-dependent for stellar samples with significant age spreads.