Satellites Around Milky Way Analogs: Tension in the Number and Fraction
  of Quiescent Satellites Seen in Observations Versus Simulations
  We compare the star-forming properties of satellites around Milky Way (MW)
analogs from the Stage~II release of the Satellites Around Galactic Analogs
Survey (SAGA-II) to those from the APOSTLE and Auriga cosmological zoom-in
simulation suites. We use archival GALEX UV imaging as a star-formation
indicator for the SAGA-II sample and derive star-formation rates (SFRs) to
compare with those from APOSTLE and Auriga. We compare our detection rates from
the NUV and FUV bands to the SAGA-II H$\alpha$ detections and find that they
are broadly consistent with over $85\%$ of observed satellites detected in all
three tracers. We apply the same spatial selection criteria used around SAGA-II
hosts to select satellites around the MW-like hosts in APOSTLE and Auriga. We
find very good overall agreement in the derived SFRs for the star-forming
satellites as well as the number of star-forming satellites per host in
observed and simulated samples. However, the number and fraction of quenched
satellites in the SAGA-II sample are significantly lower than those in APOSTLE
and Auriga below a stellar mass of $M_*\sim10^{8}\,M_{\odot}$, even when the
SAGA-II incompleteness and interloper corrections are included. This
discrepancy is robust with respect to the resolution of the simulations and
persists when alternative star-formation tracers are employed. We posit that
this disagreement is not readily explained by vagaries in the observed or
simulated samples considered here, suggesting a genuine discrepancy that may
inform the physics of satellite populations around MW analogs.
