Extending Ultra-Diffuse Galaxy Abundances to Milky Way Analogs

TL;DR

This study extends the relation between ultra-diffuse galaxy counts and host halo mass to lower mass hosts, revealing a nearly linear scaling and challenging formation models requiring dense environments.

Contribution

It provides the first empirical $N_{UDG}-M_{200}$ relation for Milky Way-like halos down to $10^{11.6} M_{\u200b ext{ } }$ and compares it with previous data, highlighting the environmental independence.

Findings

The $N_{UDG}-M_{200}$ relation is nearly linear with a slope of 0.89.

UDG abundance scales with host halo mass over three orders of magnitude.

The relation suggests UDG formation does not require high-density environments.

Abstract

We extend the Ultra-Diffuse Galaxy (UDG) abundance relation, $N_{UDG}-M_{200}$, to lower halo mass hosts $(M_{200}\sim10^{11.6-12.2}M_{\odot})$. 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 $M_{200}\sim10^{12}M_{\odot}$ 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 $N_{UDG} = (38\pm5)\cdot(\frac{M_{200}}{10^{14}})^{0.89\pm0.04}$. 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.