Time for a quick post, and a follow-up paper to this one which I posted recently. 

As I mentioned, one of the key things people are looking at at the moment is whether the dark sector, which includes dark matter and dark energy, can evolve, change and interact over time. We're keen to understand the influence of an evolving dark sector on the formation and evolution of structure in the Universe, and for that we need numerical simulations.

Now, these simulations are not easy. To get enough resolution, you need to run them on supercomputers, and you also need to be careful that you have correctly included the required physics. And that's what we have. The goal of this second paper is to ask the question "How does an evolving dark sector influence the number and properties of galaxy clusters in the Universe?"

Galaxy clusters are the biggest agglomerations of mass in the Universe, so they are easy to find in our simulations. 

As I mentioned, the interacting dark sector has to be quite subtle (or we would have worked out its properties by now) and in terms of the number of clusters we have in our range of universes with a specific mass, the interacting models seem no different to the standard cosmological models.

When we start to look at the more detailed properties of the clusters, such as how the baryons (i.e. atoms) are distributed, we find there are subtle differences.

We can see these baryons in clusters as a hot gas surrounding the galaxies, so this could be a potential probe of the true goings-on in the dark sector.

We do look at other properties of the clusters, their spins and alignments, and while there are differences, they are small and would he hard to discern observationally.

But now we have our new software for generating synthetic universes, the goal will be to push the resolution higher and higher, to uncover individual galaxies like our own Milky Way. There will definitely be new results on the nature of the dark sector, so watch this space. 

Well done Edoardo!

Hydrodynamical simulations of coupled and uncoupled quintessence models II: Galaxy clusters

Edoardo Carlesi, Alexander Knebe, Geraint F. Lewis, Gustavo Yepes

(Submitted on 21 Jan 2014)

We study the z=0 properties of clusters (and large groups) of galaxies within the context of interacting and non-interacting quintessence cosmological models, using a series of adiabatic SPH simulations. Initially, we examine the average properties of groups and clusters, quantifying their differences in LCDM, uncoupled Dark Energy (\ude) and coupled Dark Energy (\cde) cosmologies. In particular, we focus upon radial profiles of the gas density, temperature and pressure, and we also investigate how the standard hydrodynamic equilibrium hypothesis holds in quintessence cosmologies. While we are able to confirm previous results about the distribution of baryons, we also find that the main discrepancy (with differences up to 20%) can be seen in cluster pressure profiles. We then switch attention to individual structures, mapping each halo in quintessence cosmology to its \LCDM\ counterpart. We are able to identify a series of small correlations between the coupling in the dark sector and halo spin, triaxiality and virialization ratio. When looking at spin and virialization of dark matter haloes, we find a weak (5%) but systematic deviation in fifth force scenarios from \LCDM.