Hundreds of Milky Way Satellites? Luminosity Bias in the Satellite Luminosity Function

TL;DR

This paper corrects for luminosity bias in the Milky Way satellite luminosity function, estimating a much larger satellite population consistent with CDM models, and discusses future survey prospects.

Contribution

It provides a corrected satellite luminosity function using SDSS data and simulations, addressing the missing satellites problem and predicting future survey discoveries.

Findings

Estimated 300-600 satellites brighter than known dwarfs within 400 kpc

Radial distribution of known dwarfs aligns with subhalo predictions

Future surveys will complete the satellite census and constrain dark matter properties

Abstract

We correct the observed Milky Way satellite luminosity function for luminosity bias using published completeness limits for the Sloan Digital Sky Survey DR5. Assuming that the spatial distribution of Milky Way satellites tracks the subhalos found in the Via Lactea LCDM N-body simulation, we show that there should be between ~300 and ~600 satellites within 400 kpc of the Sun that are brighter than the faintest known dwarf galaxies, and that there may be as many as ~ 1000, depending on assumptions. By taking into account completeness limits, we show that the radial distribution of known Milky Way dwarfs is consistent with our assumption that the full satellite population tracks that of subhalos. These results alleviate the primary worries associated with the so-called missing satellites problem in CDM. We show that future, deep wide-field surveys such as SkyMapper, the Dark Energy Survey (DES), PanSTARRS, and the Large Synoptic Survey Telescope (LSST) will deliver a complete census of ultra-faint dwarf satellites out to the Milky Way virial radius, offer new limits on the free-streaming scale of dark matter, and provide unprecedented constraints on the low-luminosity threshold of galaxy formation.