Systematically Measuring Ultra-Diffuse Galaxies (SMUDGes). IV. Ultra-Diffuse Satellites of Milky Way Analogs

TL;DR

This study measures the distribution and properties of ultra-diffuse galaxy satellites around Milky Way analogs, revealing their abundance, mass, and color dominance, and supports models linking UDG formation to low-mass galaxy formation.

Contribution

It provides the first detailed correlation function analysis of UDG satellites around Milky Way-like galaxies, showing their distribution, abundance, and mass relation, supporting a formation model tied to low-mass galaxy processes.

Findings

UDG satellites have a radial distribution similar to normal satellites.

On average, each Milky Way analog hosts about 0.5 UDG satellites.

Most UDG satellites are red and constitute about 10% of satellite populations.

Abstract

To better understand the formation of large, low surface brightness galaxies, we measure the correlation function between ultra-diffuse galaxy (UDG) candidates and Milky Way analogs (MWAs). We find that (1) the projected radial distribution of UDG satellites (projected surface density $\propto r^{-0.84\pm0.06}$) is consistent with that of normal satellite galaxies, (2) the number of UDG satellites per MWA ($S_{\rm UDG}$) is $\sim 0.5\pm0.1$ over projected radii from 20 to 250 kpc and $-17< M_r < -13.5$, (3) $S_{\rm UDG}$ is consistent with a linear extrapolation of the relationship between the number of UDGs per halo vs. halo mass obtained over galaxy group and cluster scales, (4) red UDG satellites dominate the population of UDG satellites ($\sim80$%), (5) over the range of satellite magnitudes studied, UDG satellites comprise $\sim$ 10% of the satellite galaxy population of MWAs, (6) a significant fraction of these ($\sim$13%) have estimated total masses $>$ 10$^{10.9}$ M$_\odot$ or, equivalently, at least half the halo mass of the LMC, and populate a large fraction ($\sim$ 18%) of the expected subhalos down to these masses. All of these results suggest a close association between the overall low mass galaxy population and UDGs, which we interpret as favoring models where UDG formation principally occurs within the general context of low mass galaxy formation over models invoking more exotic physical processes specifically invoked to form UDGs.