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Surface photometry detections of red and exceedingly faint halos aroundgalaxies have resurrected the old question of whether some non-negligiblefraction of the missing baryons of the Universe could be hiding in the form offaint, hydrogen-burning stars. The optical/near-infrared colours of these redhalos have proved very difficult to reconcile with any normal type of stellarpopulation, but can in principle be explained by advocating a bottom-heavystellar initial mass function. This implies a high stellar mass-to-light ratioand hence a substantial baryonic mass locked up in such halos. Here, we explorethe constraints imposed by current observations of ordinary stellar halosubdwarfs on a putative red halo of low-mass stars around the Milky Way.Assuming structural parameters similar to those of the red halo recentlydetected in stacked images of external disk galaxies, we find that a smoothhalo component with a bottom-heavy initial mass function is completely ruledout by current star count data for the Milky Way. All viable smooth red halomodels with a density slope even remotely similar to that of the stacked halomoreover contain far too little mass to have any bearing on the missing-baryonproblem. However, we note that these constraints can be sidestepped if the redhalo stars are locked up in star clusters, and discuss potential observationsof other nearby galaxies that may be able to put such scenarios to the test.

Are the red halos of galaxies made of low-mass stars? Constraints from subdwarf star counts in the Milky Way halo