They're not collecting all of this data to make pretty pictures, it's going to be used to test all sorts of theories. Ones that explain Dark Matter as well.
(I do agree with Angela Collier, youtuber nee physicst, Dark Matter is not a theory, it's an observation. We've looked out into the universe and have seen something that we call Dark Matter that our current theories don't match up with.)
This feels like you'd say that just because apples fall from trees and a bowling ball falls in much the same way when tossed off a building, that grouping those things together implies a common cause and that we should call that cause a theory because we aren't 100% certain that they are caused by the same effect.
They could be two different reasons.
I do prefer Occom's razor for these things. We've seen a bunch extremely large celestial objects move in ways that our models cannot account for with the things that we can see. Sure, there could be more than one thing out there causing all of those extremely similar effects. But that's far less likely than there just being one reason.
It's pretty reasonable to invoke occam's razor for claiming that in general unexpected galaxy rotation curves have a common explanation. It's another thing to claim without blinking an eye that these are phenomenologically connected to baryon acuoustic oscillations in the CMB (which is what Angela does)
Since it's been a _long_ time since my physics undergrad I honestly can not speak to how baryon acoustic oscillations tie into dark matter. Hell the paper describing it came out after my first trip through college!
I'll confess the paper is a bit over my head. Astrophysics was never my passion and I became a software engineer right out of college anyways, so I'm a little rusty. However, in the 2005 paper they state that the BAO, specifically the way that the BAO has propagated, can't be explained by baryonic matter alone, which in their words would show a much larger effect than observed. This seems to be yet another observation that is consistent with dark matter.
However, since you must be a working astrophysicist, could you enlighten me with what you think is wrong with the interpretation of those observations? Do you think the >3 sigma confidence isn't enough for astrophysics?
I am genuinely curious.
it's a theory. when you present multiple observations just the fact that you group them together is not a value-free action and implies a common cause. calling it an observation is a crude and philosophically improper attempt to elevate it to a less refutable status.