Can I confirm that the background radiation is from out of our galaxy?
Well, the CMB appears to be hugely red shifted, that might be a clue.
Do you mean this?
(Btw, I have changed the level of this thread to "B".)
Yes but I am after a fact to prove it's from out of our galaxy, you know ? Can only see inferences
Yes. Very, very far from our galaxy. This is apparent because it travels through the dust in our galaxy, and the radiation is effected as a result. We can also see the impact of far-away galaxy clusters on the CMB radiation (through the https://en.wikipedia.org/wiki/Sunyaev%E2%80%93Zel'dovich_effect]Sunyaev-Zel'dovich[/PLAIN] [Broken] effect), so it definitely comes from behind them as well.
Gravitational lensing of the CMB; https://arxiv.org/abs/1502.01591, Planck 2015 results. XV. Gravitational lensing, should be sufficient to dispel any lingering doubts.
Would it be accurate to say the CMB we detect today came from outside the galaxy, but CMB originally radiated from all points in the universe, including our own?
The CMB emitted from nearby departed our neighborhood long ago, so it does not contaminate CMB emitted by distant sources - assuming that is where you were leading.
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