The Cusp/Core Problem in Galactic Halos: Long-Slit Spectra for a Large Dwarf Galaxy Sample

We derive inner dark matter halo density profiles for a sample of 165 low-mass galaxies using rotation curves obtained from high-quality, long-slit optical spectra assuming minimal disks and spherical symmetry. For \ρ(r) \~ r-\α near the galaxy center we measure median inner slopes ranging from \αₘ = 0.22 \± 0.08 to \αₘ = 0.28 \± 0.06 for various subsamples of the data. This is similar to values found by other authors, and in stark contrast to the intrinsic cusps (\αᵢₙₜ\~1) predicted by simulations of halo assembly in cold dark matter (CDM) cosmologies. To elucidate the relationship between \αₘ and \αᵢₙₜ in our data, we simulate long-slit observations of model galaxies with halo shapes broadly consistent with the CDM paradigm. Simulations with \αᵢₙₜ=1/2 and 1 recover both the observed distribution of \αₘ and correlations between \αₘ and primary observational parameters such as distance and disk inclination, whereas those with \αᵢₙₜ=5/4 are marginally consistent with the data. Conversely, the hypothesis that low-mass galaxies have \αᵢₙₜ=3/2 is rejected. While the simulations do not imply that the data favor intrinsic cusps over cores, they demonstrate that the discrepancy between \αₘ and \αᵢₙₜ\~1 for our sample does not necessarily imply a genuine conflict between our results and CDM predictions: rather, the apparent cusp/core problem may be reconciled by considering the impact of observing and data processing techniques on rotation curves derived from long-slit spectra.