SMALL-SCALE STRUCTURE IN THE SLOAN DIGITAL SKY SURVEY AND ΛCDM: ISOLATED ∼L* GALAXIES WITH BRIGHT SATELLITES

We use a volume-limited spectroscopic sample of isolated galaxies in the Sloan Digital Sky Survey to investigate the frequency and radial distribution of luminous (M-r less than or similar to -18.3) satellites like the Large Magellanic Cloud (LMC) around similar to L-* Milky Way (MW) analogs and compare our results object-by-object to Lambda CDM predictions based on abundance matching in simulations. We show that 12% of MW-like galaxies host an LMC-like satellite within 75 kpc (projected), and 42% within 250 kpc (projected). This implies similar to 10% have a satellite within the distance of the LMC, and similar to 40% of L-* galaxies host a bright satellite within the virialized extent of their dark matter halos. Remarkably, the simulation reproduces the observed frequency, radial dependence, velocity distribution, and luminosity function of observed secondaries exceptionally well, suggesting that Lambda CDM provides an accurate reproduction of the observed universe to galaxies as faint as L similar to 10(9) L-circle dot on similar to 50 kpc scales. When stacked, the observed projected pairwise velocity dispersion of these satellites is sigma similar or equal to 160 km s(-1), in agreement with abundance-matching expectations for their host halo masses. Finally, bright satellites around L-* primaries are significantly redder than typical galaxies in their luminosity range, indicating that environmental quenching is operating within galaxy-size dark matter halos that typically contain only a single bright satellite. This redness trend is in stark contrast to the MW's LMC, which is unusually blue even for a field galaxy. We suggest that the LMC's discrepant color might be further evidence that it is undergoing a triggered star formation event upon first infall.