The Dark Matter Distribution in the Spiral $NGC~3198$ out to 0.22
  $R_{vir}$
  We use recent very extended HI kinematics (out to 48 kpc) along with previous
H$\alpha$ kinematics of the spiral galaxy NGC 3198 in order to derive its
distribution of dark matter (DM). 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 rotation curve (URC) mass model (stellar disk $+$
Burkert halo $+$ gaseous disk), the NFW mass model (stellar disk $+$ NFW halo
$+$ gaseous disk) and the baryon $\Lambda$CDM 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. 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
($\Lambda$CDM) scenario. We find that the effects of baryonic physics modify
the original $\Lambda$CDM 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 $\sim$ 25 kpc, also this modified
baryon $\Lambda$CDM halo profile appears to create a tension with the derived
DM halo density.
