Dusty haloes of galaxies at intermediate redshifts

The presence and amount of dust in the halo matter producing narrow metal line absorption systems is still uncertain. We consider the parameter Σ a = Σ(1 + z a ), summed over the detected aborption line system redshifts z a , and ask whether radio-loud quasars at z < 2 and with a large value of the parameter Σ a are redder in the B - V colour than those with a smaller Σ a . This is anticipated if the absorption lines originate in sites which contain "normal" dust causing selective extinction. The answer is positive, and a mean intrinsic reddening e 0 per halo is consistent with 0.05, or about 0.2 B-mag extinction, roughly as expected.