Board Thread:Discussions/@comment-34567423-20180206085553/@comment-24909831-20180207065841

I think sector defence forces are quite plausible. Then again, not all sectors have any kind of centralized command or governorship. I bet that most of the stuff you've read is from FFG's Dark Heresy, which is fine, but its sectors are rather hierarchic and structured when the GW's own shit from rulebooks and codices hint towards a more chaotic kind of governmentship when it comes to sub-sectors or sectors.

Most of the sector defense is provided by the Imperial Navy, and possible Arbites detachments, anyway. Or that is how I have understood it.

But. When it comes to Space Marines hosting such human auxilias as you described, it is a no. System defence force is plausible but if you go trolling about around a, not to say multiple, sector(s) with Astartes authority (because no doubt they have it)... it is just a big no.