Testing the Picture

How can we combine our observations of large scale structure... ...with our models of structure formation...

... to learn about the universe?

Example 1: Structure grows differently in different cosmological models. For example, in low OmegaM models, structure grows a little, then stops. In high OmegaM models, structure continually grows. Why?

Adding a cosmological constant also strengthens structure formation. Why? What about in the future?

Simulations of structure in the universe at the present time under different cosmologies
Dark Matter only models (no dark energy)
Flat universes with dark matter and dark energy


Example 2: In OmegaM=1 universes, galaxy clusters are extremely rare in the high redshift Universe. Why? Remember, it takes time for clusters to grow. We know how many massive clusters there are currently. In low OmegaM universes, structure stops growing early, so there ought to be roughly the same number of massive clusters at higher redshift as now. On the other hand, in high OmegaM universes, structure is continually growing, so we should see fewer massive clusters at higher redshift.

from Borgani 2003

So here is a massive cluster at a redshift of z~1:

It really shouldn't be there if OmegaM=1!

from Bahcall et al 1997

Current estimates of OmegaM from these studies give values of OmegaM ~ 0.3 or so....