I use "set type=soa" within nslookup (although I'm at a windows box right now I think this works the same on Linux). I think the best you will find is the responsible name servers for Google's DNS domain. As to which one is the authoritative name server, I would presume this is up to Google and not really obtainable in any DNS search results? But I am guessing!
set type=soa www.google.co.uk
Server: [192.168.1.254] Address: 192.168.1.254
Non-authoritative answer: www.google.co.uk canonical name = www.google.com www.google.com canonical name = www.l.google.com www.l.google.com canonical name = www-tmmdi.l.google.com
l.google.com primary name server = ns4.google.com responsible mail addr = dns-admin.google.com serial = 1404374 refresh = 900 (15 mins) retry = 900 (15 mins) expire = 1800 (30 mins) default TTL = 60 (1 min)