Apex domains cannot have CNAME records.
Question and response
Question
dig caltech.edu. NS
Answer
caltech.edu. 5 NS ns0090.secondary.cloudflare.com.
caltech.edu. 5 NS ns0239.secondary.cloudflare.com.
Authority
The response has no authority records.
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0