Deep HST/UVIS imaging of the candidate dark galaxy CDG-1

TL;DR

This study uses HST imaging to set upper limits on diffuse light in the candidate dark galaxy CDG-1, suggesting it may be a globular cluster grouping rather than a true dark galaxy.

Contribution

The paper provides new constraints on the stellar luminosity of CDG-1, improving understanding of its nature and testing its classification as a dark galaxy.

Findings

No diffuse emission detected, with a surface brightness limit of >28.1 mag/arcsec$^2$

Globular clusters constitute at least 50% of the total luminosity

CDG-1 could be a chance grouping of globular clusters in Perseus

Abstract

CDG-1 is a tight grouping of four likely globular clusters in the Perseus cluster, and a candidate dark galaxy with little or no diffuse light. Here we provide new constraints on the luminosity of any underlying stellar emission, using HST/UVIS F200LP imaging. No diffuse emission is detected, with a 2$\sigma$ upper limit of F200LP>28.1 mag/arcsec$^2$ on the 5'' scale of CDG-1. This surface brightness limit corresponds to a 2$\sigma$ lower limit of >0.5 for the fraction of the total luminosity that is in the form of globular clusters. The most likely alternative, although improbable, is that CDG-1 is a chance grouping of four globular clusters in the halo of the Perseus galaxy IC312.