The Authority section indicates the server(s) that are the ultimate authority for answering DNS queries about that domain.
The reason for this section is that you can query any* DNS server(s) to answer a query for you. That server may choose though to answer the query from a cache. However, if you want to ensure you get an authoritative response ("from the horses mouth" so to speak) - you should ask the server(s) in the authority section.
(* = Any server which will accept your query, that is.)
