Panel a: flux density of the NE image (in XX and YY polarization products, as well as in Stokes I); panel b: flux density of the SW image (same products as those of NE shown in panel a); panel c: flux-density ratios between NE and SW; panel d polarization ratio, R_pol (see text). All quantities are shown as a function of parallactic angle, ψ, rotated by the feed angle of the Band 9 receivers at ALMA, β_B9.