Systematically Measuring Ultradiffuse Galaxies (SMUDGes). IV. Ultradiffuse Satellites of Milky Way Analogs

To better understand the formation of large, low-surface-brightness galaxies, we measure the correlation function between ultradiffuse galaxy (UDG) candidates and Milky Way analogs (MWAs). We find that: (1) the projected radial distribution of UDG satellites (projected surface density ∝r <SUP>-0.84±0.06</SUP>) is consistent with that of normal satellite galaxies; (2) the number of UDG satellites per MWA (S <SUB>UDG</SUB>) is ~0.5 ± 0.1 over projected radii from 20 to 250 kpc and -17 &lt; M <SUB> r </SUB> &lt; -13.5; (3) S <SUB>UDG</SUB> is consistent with a linear extrapolation of the relationship between the number of UDGs per halo versus halo mass obtained over galaxy group and cluster scales; (4) red UDG satellites dominate the population of UDG satellites (~80%); (5) over the range of satellite magnitudes studied, UDG satellites comprise ~10% of the satellite galaxy population of MWAs; and (6) a significant fraction of these (~13%) have estimated total masses &gt;10<SUP>10.9</SUP> M <SUB>⊙</SUB> or, equivalently, at least half the halo mass of the LMC, and populate a large fraction (~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.