A link between feedback outflows and satellite galaxy suppression

We suggest a direct, causal link between the two ‘missing’ baryon problems of contemporary galaxy formation theory: (1) that large galaxies (such as the Milky Way) are known to contain too little gas and stars and (2) that too few dwarf satellite galaxies are observed around large galaxies compared with cosmological simulations. The former can be explained by invoking some energetic process – most likely active galactic nucleus or star formation feedback – which expels to infinity a significant fraction of the gas initially present in the protogalaxy, while the latter problem is usually explained by star formation feedback inside the dwarf or tidal and ram pressure stripping of the gas from the satellite galaxy by its parent. Here we point out that the host galaxy ‘missing’ baryons, if indeed ejected at velocities of hundreds to a thousand km s−1, must also affect smaller satellite galaxies by stripping or shocking the gas there. We estimate the fraction of gas removed from the satellites as a function of the satellite galaxy's properties, distance to the host and the strength of the feedback outflow. Applying these results to a Milky-Way-like dark matter halo, we find that this singular shock ram pressure stripping event may be quite efficient in removing the gas from the satellites provided that they are closer than ∼50–100 kpc to the host. We also use the orbital and mass modelling data for eight Galactic dwarf spheroidal (dSph) satellites, and find that it is likely that many of them have been affected by the Galactic outflow, although the current data still leave much room for uncertainties. Finally, we point out that galactic outflows of the host may also trigger a starburst in the satellite galaxies by overpressuring their gas discs. We speculate that this process may be responsible for the formation of the globular clusters observed in some of the Milky Way's dSphs (e.g. the Fornax and Sagittarius dSphs) and may also be important for the formation of the bulk stellar populations in the dSphs.