Extending Ultra-Diffuse Galaxy abundances to Milky Way analogues

Abstract

ABSTRACT We extend the Ultra-Diffuse Galaxy (UDG) abundance relation, NUDG − M200, to lower halo mass hosts $(M_{200}\sim 10^{11.6-12.2}\, \mathrm{M}_{\odot })$. We select UDG satellites from published catalogues of dwarf satellite galaxies around Milky Way analogues, namely the Exploration of Local Volume Satellites (ELVES) survey, the Satellite Around Galactic Analogs (SAGA) survey, and a survey of Milky Way-like systems conducted using the Hyper-Suprime Cam. Of the 516 satellites around a total of 75 Milky Way-like hosts, we find that 41 satellites around 33 hosts satisfy the UDG criteria. The distributions of host halo masses peak around $M_{200}\sim 10^{12}\, \mathrm{M}_{\odot }$, independent of whether the host has a UDG satellite or not. We use literature UDG abundances and those derived here to trace the NUDG − M200 relation over three orders of magnitude down to $M_{200}=10^{11.6}\, \mathrm{M}_{\odot }$ and find the best-fitting linear relation of $N_{\mathrm{ UDG}} = (38\pm 5) (\frac{M_{200}}{10^{14}})^{0.89\,\,\pm ~ 0.04}$. This sub-linear slope is consistent with earlier studies of UDG abundances as well as abundance relations for brighter dwarf galaxies, excluding UDG-formation mechanisms that require high-density environments. However, we highlight the need for further homogeneous characterization of UDGs across a wide range of environments to properly understand the NUDG − M200 relation.