The majority of the work has concentrated on mapping and measuring the 'cosmic web' - the network of filaments within which galaxies form. In local regions of the universe, it is possible to survey galaxies over the whole sky. This was done by combining optical ground-based data with infrared results from space. The optical-to-IR data give a rough measure of galaxy redshift (proportional to distance, according to Hubble's law), so the distribution can be cut into 'tomographic' slices, revealing the cosmic web at different distances. But for best accuracy, spectroscopic redshifts are required, and this is the basis for the second picture. This is from the VImos Public Extragalactic Redshift Survey (VIPERS), which was a major project of the European Southern Observatory's 8m telescopes in Chile.
The most important statistical analyses of such data concern the impact of 'peculiar velocities' - motion cause by the growth of the cosmic web. This causes anisotropic clustering that can be used to measure the amplitude of the velocities and hence the strength of gravity. We have measured this signature using the GAMA, Vipers, and SDSS-IV surveys; all the results match the predictions of standard gravity. A large part of this effort lies in developing infrastructure for generating appropriate mock surveys for the various datasets being analysed by the team.
We have also focused on understanding the relation of galaxies to dark-matter haloes, asking how different astrophysical tracers of clustering (galaxies with different star-formation rates; quasars) populate the haloes, and whether this population is affected by tidal forces that arise in different locations in the cosmic web. Despite past suggestions that such effects are present, we see no sign of an effect, making modelling of galaxy clustering a simpler task.
The other part of the effort concerns modelling galaxy formation. Part of this is 'semianalytic' - estimating physically how gas will behave in the gravitational field of dark matter - but we can also implement the physics of star formation in numerical hydrodynamical simulations. The focus is on the long-term efficiency of star formation, while varying the cosmological parameters. In three papers using the ENZO cosmological hydrodynamical code, we have shown how cosmic star formation would be suppressed in universes with a larger cosmological constant.
