If it can be challenged then you not an authority are you?
However you can talk about Piccasso, where he was born, how many kids, wives, where he was when he was in his blue period etc, without worrying about the aesthetics and you can be an authority on Picasso with no subjectivity required.
Like wise you can be an authority on the whtys and wherefores of politics, the history, the decesions and why they were taken without having to side with one side or the other. This would make you a political authority.
Subjectivity is in the end product, the painting or the decision not in how it got there.
You can be an authority on Art or Politics without ever having to be subjective.