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

Abstract

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

17 pages, 14 figures; uses emulateapj. Accepted for publication in AJ. Minor changes made to match AJ proofs