Extending Ultra-Diffuse Galaxy Abundances to Milky Way Analogs

We extend the Ultra-Diffuse Galaxy (UDG) abundance relation, $N_{UDG}-M_{200}$, to lower halo mass hosts $(M_{200}\sim {10}^{11.6-12.2}{M}_{\odot })$. We select UDG satellites from published catalogs of dwarf satellite galaxies around Milky Way analogs, namely the Exploration of Local Volume Satellites (ELVES) survey, 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 41 satellites around 33 hosts satisfy the UDG criteria. The distributions of host halo masses peak around $M_{200}\sim {10}^{12}{M}_{\odot }$ independent of whether the host has a UDG satellite or not. We use literature UDG abundances and those derived here to trace the $N_{UDG}-M_{200}$ relation over three orders of magnitude down to $M_{200}={10}^{11.6}{M}_{\odot }$ and find a best-fit linear relation of $N_{UDG}=(38\pm 5)\cdot (\frac{M_{200}}{{10}^{14}}{)}^{0.89\pm 0.04}$. 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 $N_{UDG}-M_{200}$ relation.