Forward-modelling the luminosity, distance, and size distributions of the Milky Way satellites

We use GRUMPY, a simple regulator-type model for dwarf galaxy formation and evolution, to forward model the dwarf galaxy satellite population of the Milky Way (MW) using the Caterpillar zoom-in simulation suite. We show that luminosity and distance distributions of the model satellites are consistent with the distributions measured in the DES, PS1, and SDSS surveys, even without including a model for the orphan galaxies. We also show that our model for dwarf galaxy sizes can simultaneously reproduce the observed distribution of stellar half-mass radii, r(1/2), of the MW satellites and the overall r(1/2)-M-* relation exhibited by observed dwarf galaxies. The model predicts that some of the observed faint stellar systems with r(1/2) < 10 pc are ultra-faint dwarf galaxies. Scaling of the stellar mass M-* and peak halo mass M-peak for the model satellites is not described by a power law, but has a clear flattening of M-*-M-peak scaling at M-peak < 10 M-circle dot imprinted by reionization. As a result, the fraction of low mass haloes (M-peak < 10(8), M-circle dot) hosting galaxies with M-V < 0 is predicted to be 50 per cent at M-peak similar to 3.6 x 10(7) M-circle dot. We find that such high fraction at that halo mass helps to reproduce the number of dwarf galaxies discovered recently in the HSC-SSP survey. Using the model we forecast that there should be the total of 440(+201)(-147) (68 per cent confidence interval) MW satellites with M-V < 0 and r(1/2) > 10 pc within 300 kpc and make specific predictions for the HSC-SSP, DELVE-WIDE, and LSST surveys.

Automated summary

By using the GRUMPY model to forward model dwarf galaxy formation and evolution, we found that the luminosity and distance distributions of model satellites are consistent with those measured in surveys. Additionally, the model can simultaneously reproduce the observed distribution of stellar half-mass radii of MW satellites and the overall r(1/2)-M-* relation observed in dwarf galaxies.