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 $\rho® \sim r^{-\alpha}$ near the galaxy center we measure median inner slopes ranging from ${\alpha }_m=0.22\pm 0.08$ to $0.28\pm 0.06$ for various subsamples of the data. This is similar to values found by other authors, and in stark contrast to the intrinsic cusps (${\alpha }_{int}\sim 1$) predicted by simulations of halo assembly in cold dark matter (CDM) cosmologies. To elucidate the relationship between ${\alpha }_m$ and ${\alpha }_{int}$ in our data, we simulate long-slit observations of model galaxies with halo shapes broadly consistent with the CDM paradigm. Simulations with ${\alpha }_{int}=1\mathrm{/}2$ and 1 recover both the observed distribution of ${\alpha }_m$ and correlations between ${\alpha }_m$ and primary observational parameters such as distance and disk inclination, whereas those with ${\alpha }_{int}=5\mathrm{/}4$ are marginally consistent with the data. Conversely, the hypothesis that low-mass galaxies have ${\alpha }_{int}=3\mathrm{/}2$ is rejected. While the simulations do not imply that the data favor intrinsic cusps over cores, they demonstrate that the discrepancy between ${\alpha }_m$ and ${\alpha }_{int}\sim 1$ 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.