import yt
ds = yt.load('IsolatedGalaxy/galaxy0030/galaxy0030')
slc = yt.SlicePlot(ds, 'z', 'velocity_x')
WARNING:yt:Plot image for field ('gas', 'velocity_x') has both positive and negative values. Min = -26589184.944230, Max = 26397689.631420. WARNING:yt:Switching to symlog colorbar scaling unless linear scaling is specified later
slc
slc.set_log('velocity_x', True, linthresh=1e6)