Source clustering in the Hi-GAL survey determined using a minimum spanning tree method

TL;DR

This study uses a minimum spanning tree method to identify and analyze over-densities and cluster candidates in the Hi-GAL survey, revealing their distribution, fractal nature, and mass functions consistent with the Kroupa IMF.

Contribution

It introduces a novel application of the MST method to identify and refine star cluster candidates in the Hi-GAL survey, including distance folding for reliability.

Findings

Identified 1,633 over-densities with >10 members.

496 are reliable cluster candidates with distances; 1,137 are potential candidates.

Clusters follow the Milky Way's spiral structure and are fractal in distribution.

Abstract

The aims are to investigate the clustering of the far-infrared sources from the Herschel infrared Galactic Plane Survey (Hi-GAL) in the Galactic longitude range of -71 to 67 deg. These clumps, and their spatial distribution, are an imprint of the original conditions within a molecular cloud. This will produce a catalogue of over-densities. The minimum spanning tree (MST) method was used to identify the over-densities in two dimensions. The catalogue was further refined by folding in heliocentric distances, resulting in more reliable over-densities, which are cluster candidates. We found 1,633 over-densities with more than ten members. Of these, 496 are defined as cluster candidates because of the reliability of the distances, with a further 1,137 potential cluster candidates. The spatial distributions of the cluster candidates are different in the first and fourth quadrants, with all clusters following the spiral structure of the Milky Way. The cluster candidates are fractal. The clump mass functions of the clustered and isolated are statistically indistinguishable from each other and are consistent with Kroupa's initial mass function.