J-PLUS: A catalogue of globular cluster candidates around the M81/M82/NGC3077 triplet of galaxies

TL;DR

This study uses multi-band J-PLUS imaging to identify and analyze 642 new globular cluster candidates around the M81/M82/NGC3077 triplet, revealing their spatial distribution, potential connections, and metallicity properties.

Contribution

Introduces a novel PCA-based classification method for GC candidate identification using multi-band photometry, significantly increasing known candidates around the galaxy triplet.

Findings

Discovery of 642 new GC candidates around the triplet

Evidence of a GC bridge connecting M81 and M82

Broad metallicity distribution with a metal-rich bump

Abstract

Globular clusters (GCs) are proxies of the formation assemblies of their host galaxies. However, few studies exist targeting GC systems of spiral galaxies up to several effective radii. Through 12-band Javalambre Photometric Local Universe Survey (J-PLUS) imaging, we study the point sources around the M81/M82/NGC3077 triplet in search of new GC candidates. We develop a tailored classification scheme to search for GC candidates based on their similarity to known GCs via a principal components analysis (PCA) projection. Our method accounts for missing data and photometric errors. We report 642 new GC candidates in a region of 3.5 deg$^2$ around the triplet, ranked according to their Gaia astrometric proper motions when available. We find tantalising evidence for an overdensity of GC candidate sources forming a bridge connecting M81 and M82. Finally, the spatial distribution of the GC candidates $(g-i)$ colours is consistent with halo/intra-cluster GCs, i.e. it gets bluer as they get further from the closest galaxy in the field. We further employ a regression-tree based model to estimate the metallicity distribution of the GC candidates based on their J-PLUS bands. The metallicity distribution of the sample candidates is broad and displays a bump towards the metal-rich end. Our list increases the population of GC candidates around the triplet by 3-fold, stresses the usefulness of multi-band surveys in finding these objects, and provides a testbed for further studies analysing their spatial distribution around nearby (spirals) galaxies.