New Constraints on the Halo Mass of Ultra-Diffuse Galaxies with UNIONS using Weak Gravitational Lensing

Abstract

While a lot of progress has been made in detecting and measuring various properties of Ultra-diffuse Galaxies (UDGs) over the last decade, the dark matter halo mass of these extremely faint and large objects remains a mystery. A better constraint on the total halo mass of UDGs would disentangle the wide variety of proposed formation mechanisms. We detect a contaminated sample of 545 potential UDGs, of which we estimate 290 to be true UDGs, in the ongoing Ultraviolet Near Infrared Optical Northern Sky Survey (UNIONS) using the Canada-France Imaging Survey (CFIS) r-band imaging, limiting our search to within 66 galaxy clusters up to redshift z ≤ 0.1. From weak gravitational lensing measurement around our UDG sample corrected for interloper contamination, we find an excess surface density consistent with zero (no detection) and a 2σ upper limit on the average halo mass of m200 ≤ 10^12.51 M⊙. By combining our measurement with that of Sifón et al. (2018), the only other weak gravitational lensing measurement of UDGs, we are able to constrain the halo mass further with a 2σ upper limit of m200 ≤ 10^12.05 M⊙ when accounting for the potential low-biasing effect of interlopers in this combined sample. Our results do not disentangle whether UDGs tend to be, on average, more dark matter-dominated or dark matter-deficient galaxies and therefore does not allow us to put new constraints on their formation mechanism. This work on UDG detection in a wide field survey optimized for weak lensing helps pave the way for future direct halo mass measurements of UDGs in upcoming surveys such as the Euclid Wide Survey.