Relations between IGM proton column density and characteristic micro-turbulence velocities in regions S1 (red) and N1 (black) with derived proton columns (vertical lines). q = 0 and q = 1 refer to inhomogeneous and homogeneous distribution of emitting and absorbing ions, respectively. The blue lines are the 1- and 2σ upper limits for mean turbulent velocities in the NGC 4636 core regions, and the green dashed line marks the limit where turbulent heating is expected to balance gas cooling (see Pinto et al. 2015).