profile; we discuss possible issues with the asymmetric drift in § 7.3. To verify that the halo is cuspy, we conducted a MCMC run in which the cusp value was fixed to 0. The resulting rotation curve fit is shown in Fig. 18; the fit is clearly very poor. There is a pronounced kink in the rotation curve that is not observed, and neither the gas nor the stellar rotation curves are properly fit. We therefore reject models with γ = 0. The issue of halo cuspiness remains unsettled. It is often argued that galaxies demon- strate evidence of cored halos (Blais-Ouellette et al. 2001; de Blok et al. 2001), but many complications present themselves. Some researchers find that the rotation curves used to probe halo central structure are consistent with both cored and cuspy profiles, in part be- cause of the size of the uncertainties (van den Bosch & Swaters 2001; Swaters et al. 2003; Dutton et al. 2005; Simon et al. 2005; Spekkens et al. 2005). Further caveats concern the correct interpretation of the rotation curve; the presence of noncircular gas motions, as might be caused by a triaxial halo, and the presence of turbulence caused by supernova feedback and the magnetorotational instability point to the complexity of the problem (Hayashi et al. 2004; Rhee et al. 2004; Valenzuela et al. 2007; Tamburro et al. 2009). Some steps towards resolving these issues are taken by Oh et al. 2008, who find that the non-circular motions in their sample cannot rectify the discrepancy. In fact Begeman (1987) finds that noncircular motions in H I are small in NGC 6503. However, Tamburro et al. (2009) find relatively consistent values of ∼ 5 − 25 km s − 1 for the H I dispersion across their sample of late type galaxies, and the calculated star formation for NGC 6503 ( § 5.1) is consistent with their mea- surements. Therefore it is safe to assume that the H I dispersion of NGC 6503 is ∼ 5 − 25 km s − 1 and probably driven by supernova-induced turbulence inside the optical radius. More- over, as noted in § 2.2, the H I rotation is systematically larger than the H β rotation, which suggests that the H β rotation is more affected by these issues. Recent simulations suggest that halo cusps are slightly shallower than previously in- ferred, with γ = 0 . 9 ± 0 . 1 (Navarro et al. 2008). However, halos are subject to multiple effects due to baryons that are not accounted for in cosmological simulations, which may help explain why our cusp values are larger than found by Navarro et al. The full effect of baryonic physics on halo profiles is still poorly understood, but Abadi et al. (2009) find that the central density increases when more detailed baryonic effects are included. The central density cusp may also be affected by bar formation; Weinberg & Katz (2002) argue that bars are capable of washing out central cusps, an effect seen in Holley-Bockelmann et al. (2005) and Weinberg & Katz (2007). However, Sellwood (2003, 2008) argues that bar formation can draw mass inward, increasing the strength of the cusp; Dubinski et al. (2008) find with their simulations that a live bar maintains the cusp. The differences in cusp evolution may be due to differences in the codes used. If NGC 6503 did once possess a bar, our results 22