The Kett are not from Andromeda at all. Several points in the game show they are an intergalactic species who came to andromeda to exault the native races. This is why there is more than one Archon.
Also its pretty much a given the Jaardan are not native to Andromeda either. You don't build a self powered Dyson sphere that can travel around and act as a pan galactic terraforming hub just to plop it down in your own galaxy. If they were native, they would have been around a lot longer than the 600 years its taken the Initiative to get there. We would have seen evidence of "ancient" ruins, not just a few hundred year old ones if they were native.
Cut and pasted for your reference.
Sarhesen is the homeworld of the kett, located in an unknown system of the Andromeda galaxy. It is the capital of the Kett Empire and seat of its Senate. According to kett history, Sarhesen was united by the invention of exaltation.
I stand corrected. None of the data I read mentioned the homeworld as in the Andromeda system itself. However, I would like to reserve my opinion simply as its a wiki and anyone can edit it. If someone could point toward where in the game the info is, I would happily check it myself.
I think you learn about the kett empire more during the side quests "Know Your Enemy and Dissension in the Ranks" There is comms recordings between the kett as you progress iirc.
