Monday

The Milky Way's population of dwarf satellite galaxies can be used to make inferences about the nature of Dark Matter (DM) and galaxy formation physics. Presently, a complete census of these objects does not exist, necessitating estimates of the total from partial surveys. Many previous estimates lacked the survey data that are now available and also suffered from limitations in the extrapolation technique employed.

We overcome these difficulties by using observations from both the Sloan Digital Sky Survey (SDSS) Data Release 9 and Dark Energy Survey (DES) surveys – which together cover nearly half of the sky – and by introducing a new Bayesian inference method. We apply this technique to a set of 5 highly-resolved DM-only Milky Way (MW) analogues from the AQUARIUS simulation suite, predicting fewer satellites than previous studies which only used earlier SDSS data releases. We find only a weak dependence on MW halo mass at fainter absolute magnitudes, and predict that half of the total satellite population is potentially observable by the forthcoming Large Synoptic Survey Telescope (LSST). These new estimates offer insights into the physics of galaxy evolution, and can be used to place further constraints on allowed DM cosmological models.