Apex domains cannot have CNAME records.
Question and response
Question
dig northwestern.edu. NS
Answer
northwestern.edu. 5 NS accuvax.northwestern.edu.
northwestern.edu. 5 NS cicada.northwestern.edu.
Authority
The response has no authority records.
Additional
cicada.northwestern.edu. 5 A 18.216.244.66
accuvax.northwestern.edu. 5 A 129.105.49.100
cicada.northwestern.edu. 5 AAAA 2600:1f16:ad6:2302:0:0:0:100
accuvax.northwestern.edu. 5 AAAA 2620:10d:2010:6011:0:0:0:100
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0