Top panel: derived intensity ratio between the XX and the YY correlations () from the Ci line velocity channel synthesized image, as a function of v_lsr. We overplotted the XX and YY intensity ratios derived from the continuum data of the inner 7 12 m array mosaic fields (dashed lines, color coding the four spectral windows). The large scattering in the redshifted and blueshifted ends are because we did not detect Ci emission or absorption in those channels, and therefore fittings of did not converge. We performed linear regression for the high S/N spectral channels, and derived the ±1 standard deviation () of the differences from the regression line. The result of the linear regression is shown by light blue symbols. We plot ()/() in the bottom panel.