There are some DNS concepts which people sometimes confuse with the split between authoritative and recursive nameservice.
This refers to the way that the authoritative servers in the DNS namespace are 'found' by recursive servers. Delegation is what happens when the administrators for a parent domain (e.g. test.com provide within their zone the details of the nameservers for mytest.test.com - although this doesn't mean that the servers so named can actually answer any queries for names in mytest.test.com). Having a zone delegated to your server doesn't (by itself) make it an authoritative server - it also needs to be configured to serve that zone.
Conversely, people sometimes are confused into thinking that their servers are not authoritative because there is no delegation to them. However, there is nothing preventing a nameserver operator from configuring their server to provide an authoritative answer for a zone for which they have not been delegated authority, and many operators choose to do this for a variety of reasons. Those servers are performing an authoritative function.
Master and Slave Servers
Slave servers, even though they receive a copy of their zone data from a master server, still answer queries authoritatively from locally stored zone data and not by recursing. Slave servers are authoritative servers for the zones they are slaving.