An automated method to detect and characterise semi-resolved star clusters

TL;DR

This paper introduces an automated technique for detecting and characterizing semi-resolved star clusters in large astronomical surveys, demonstrated on the LMC with high detection accuracy and low contamination.

Contribution

The method uniquely combines PSF modeling, isophote analysis, and integrated photometry to identify semi-resolved clusters in crowded, nebular regions, improving automation and accuracy.

Findings

Detected 682 candidate clusters in a challenging LMC region.

Achieved approximately 80% validation rate with JWST data.

Estimated contamination rate of 13% from non-cluster objects.

Abstract

We present a novel method for automatically detecting and characterising semi-resolved star clusters: clusters where the observational point-spread function (PSF) is smaller than the cluster's radius, but larger than the separations between individual stars. We apply our method to a 1.77 deg$^2$ field located in the Large Magellanic Cloud (LMC) using the VISTA survey of the Magellanic Clouds (VMC), which surveyed the LMC in the $YJK_\text{s}$ bands. Our approach first models the position-dependent PSF to detect and remove point sources from deep $K_\text{s}$ images; this leaves behind extended objects such as star clusters and background galaxies. We then analyse the isophotes of these extended objects to characterise their properties, perform integrated photometry, and finally remove any spurious objects this procedure identifies. We demonstrate our approach in practice on a deep VMC $K_\text{s}$ tile that contains the most active star-forming regions in the LMC: 30 Doradus, N158, N159, and N160. We select this tile because it is the most challenging for automated techniques due both to crowding and nebular emission. We detect 682 candidate star clusters, with an estimated contamination rate of 13% from background galaxies and chance blends of physically unrelated stars. We compare our candidates to publicly available James Webb Space Telescope data and find that at least 80% of our detections appear to be star clusters.