Galaxy bias and baryon acoustic oscillations (BAO) I have a doubt with the concept of galaxy bias and how it affects baryon acoustic oscillations, it is supposed to mean that by measuring the distribution of galaxies we are not measuring the actual distribution of dark matter (I imagine this is due to processes of galaxy formation?). But since baryon acoustic oscillations affect the baryons, why do we need to know the dark matter distribution?
 A: You are correct about the bias factor - because the dark matter distribution is not measured directly, but via tracers (galaxies), there may be some bias in the tracers. This is put into the analysis as an unknown bias parameter $b$ that needs to be fit.
Now the second part of your question - why do we care about the dark matter? Briefly, it is because the dark matter and baryons mutually gravitate. Due to hydrodynamics, BAOs result in an overdensity of baryons in a shell at the sound horizon scale around an initial (random) baryon overdensity. But these overdense baryon regions are massive, and their gravity pulls in a bit of extra dark matter than the average, so there is also an overdensity in the dark matter distribution tracing the overdensity in the baryons.
Then later, galaxies form. We think every galaxy forms inside a dark matter "halo", and because of BAOs there should be more galaxies than average forming at separations equal to the sound horizon scale because (1) there is some extra dark matter there to help draw in baryons for galaxy formation, (2) there are some extra baryons to fuel galaxy formation (and their self-gravity will also help along gravitational collapse).
The baryons and dark matter are gravitationally coupled "fluids" (dark matter is typically modelled as a collisionless fluid), so they need to be considered together.
