The VMC survey - XVI. Spatial variation of the cluster-formation activity in the innermost regions of the Large Magellanic Cloud

TL;DR

This study analyzes star clusters in the innermost regions of the Large Magellanic Cloud using near-infrared photometry to determine their ages, reddening, and spatial distribution, revealing patterns of cluster formation over time.

Contribution

It provides a comprehensive, statistically complete analysis of cluster ages and reddening in the LMC's central regions, highlighting spatial and temporal variations in cluster formation.

Findings

Outer LMC bar regions experienced earlier cluster formation.

30 Doradus region shows dominance of recent cluster formation.

Cluster and field-star populations are not fully coupled in recent 100 Myr.

Abstract

We present results based on $YJK_{\rm s}$ photometry of star clusters in the Large Magellanic Cloud (LMC), distributed throughout the central part of the galaxy's bar and the 30 Doradus region. We analysed the field-star decontaminated colour--magnitude diagrams of 313 clusters to estimate their reddening values and ages. The clusters are affected by a mean reddening of $E(B-V) \in [0.2,0.3]$ mag, where the average internal LMC reddening amounts to $\sim$ 0.1--0.2 mag. The region covering 30 Doradus includes clusters with reddening values in excess of $E(B-V)$ = 0.4 mag. Our cluster sample spans the age range $7.0 \le \log(t$ yr$^{-1}) < 9.0$, represents an increase of 30 per cent in terms of the number of clusters with robust age estimates and comprises a statistically complete sample in the LMC regions of interest here. The resulting cluster frequencies suggest that the outermost regions of the LMC bar first experienced enhanced cluster formation -- $\log(t$ yr$^{-1}) \in [8.5,9.0]$ -- before the activity proceeded, although in a patchy manner, to the innermost regions, for $\log(t$ yr$^{-1}) < 7.7$. Cluster frequencies in the 30 Doradus region show that the area is dominated by very recent cluster formation. The derived star-formation frequencies suggest that the cluster and field-star populations do not seem to have fully evolved as fully coupled systems during the last $\sim$ 100 Myr.