The Dark Matter Distribution in the Spiral $NGC~3198$ out to 0.22 $R_{vir}$

Abstract

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.