Let me be clear, I'm NOT talking about relying on the opinion of an authority for advice. I'm also NOT talking about pointing to evidence that other people have collected. I'm talking about putting forth the opinion of an authority in place of reasoning and evidence, in the course of argument.
Commonly, appeals to authority are recognized, not by the mention of an authority, but by the absence of presentation of that authority's reasoning and evidence. Note that a statement of the kind, "Einstein claimed _____, therefore _____ is true" is a fallacy even if Einstein is an expert on the subject. If you are persuaded by an argument that has been presented by an authority and think others will be as well, simply present that argument (duly credited, of course).
Dawkins doesn't present an argument or evidence that proves there is no god. He can't, because the proposition that there IS a god is logically non-falsifiable. Instead, he expects his audience to rely on his authority, and accept a conclusion that he has reached intuitively.