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

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.