THE COUPLING BETWEEN THE CORE/CUSP AND MISSING SATELLITE PROBLEMS

Abstract

We calculate the energy that baryons must inject in cold dark matter (CDM)\nhaloes in order to remove centrally-divergent DM cusps on scales relevant to\nobservations of dwarf spheroidal galaxies (dSphs). We estimate that the CDM\nhaloes often associated with the Milky Way's dSphs (M_vir/M_\\odot \\sim\n10^{9-10}) require \\Delta E/erg \\sim 10^{53-55} in order to form cores on\nscales comparable to the luminous size of these galaxies. While supernova type\nII (SNeII) explosions can in principle generate this energy, the actual\ncontribution is limited by the low star formation efficiency implied by the\nabundance of luminous satellites. Considering that CDM's well-known `core/cusp'\nand `missing satellite' problems place opposing demands on star formation\nefficiencies, existing observational evidences for large cores in the most\nluminous dSphs require that CDM models invoke some combination of the\nfollowing: (i) efficient (of order unity) coupling of SNeII energy into dark\nmatter particles, (ii) star formation histories peaking at unexpectedly high\nredshifts (z>6), (iii) a top-heavy stellar IMF, and/or (iv) substantial\nsatellite disruption or other stochastic effects to ease the substructure\nabundance constraints. Our models show that the tension between CDM problems on\nsmall scales would increase if cored DM profiles were to be found in fainter\ndwarves.\n