The dark matter distribution in the spiral NGC 3198 out to 0.22 Rvir

Aims. We use recent very extended HI kinematics (out to 48 kpc) along with previous Hα kinematics of the spiral galaxy NGC 3198 in order to derive its distribution of dark matter (DM). Methods. First, we used a chi-square method to model the rotation curve (RC) of this galaxy in terms of different profiles of its DM distribution: the universal RC (URC) mass model (stellar disk + Burkert halo + gaseous disk), the NFW mass model (stellar disk + NFW halo + gaseous disk) and the baryon ΛCDM mass model (stellar disk + NFW halo modified by baryonic physics + gaseous disk). Second, to derive the DM halo density distribution, we applied a new method that does not require a global and often uncertain mass modelling. Results. While according to the standard method, both URC and NFW mass models can account for the RC, the new method instead leads to a density profile that is sharply disagrees with the dark halo density distribution predicted within the Lambda cold dark matter (ΛCDM) scenario. We find that the effects of baryonic physics modify the original ΛCDM halo densities in such a way that the resulting profile is more compatible with the DM density of NGC 3198 derived using our new method. However, at large distances, r ~ 25 kpc, also this modified baryon ΛCDM halo profile appears to create a tension with the derived DM halo density.