Google has some servers (Edge Nodes) located into ISPs for quicker response, so this seesm to beis what they call the caseGoogle Global Cache. They are basically big proxy caches for Alaska Communication Systemsserving static content (such as YouTube videos).
TheyAccording to their FAQ, it is «designed for end-user networks with greater than 1Gbps of peak Google traffic»
As you have observed, Alaska Communication Systems seems to have some servers deployed in this way. Given that they have a valid Google https certificate, so it seemsthey seem completely legitimate.