ds = load('myfile.hdf5',over_refine_factor=1)
re = ds.region(center=[750]*3, left_edge=[700]*3, right_edge=[800]*3)

ad = re.ds.all_data()
density = ad[("PartType0","density")]
wdens = np.where(density == np.max(density))
coordinates = ad[("PartType0","Coordinates")]
cen = coordinates[wdens][0]

SlicePlot(ds, 2, ('gas', 'density'), center=cen,width = (15,'kpc')).save()