The cosmic web environment of dark matter haloes: for an enhanced understanding of structure formation

Cosmological interpretation of data from galaxies and cluster surveys relies on our understanding of hierarchical structure formation in which galaxies are hosted by dark matter haloes which are biased tracers of the dark matter distribution. More often than not, this picture leaves out details of the dark matter haloes such as its assembly history and the structure of the cosmic web of its environment. For e.g, we lack a first principles understanding of the halo assembly bias, which describes the correlation between internal properties of dark matter haloes and the large-scale halo clustering (or halo bias) at fixed halo mass.

Understanding and calibrating these effects also continues to be of interest from the point of view of galaxy formation and evolution, it will also be a potential systematic in the inferences made by upcoming large-volume surveys.

Using a suite of cosmological simulations, we quantify the halo's cosmic web environment by the tidal anisotropy at 4\times halo radius. We then show that the halo assembly bias comprises two statistical links: one between the halo’s internal property and its tidal anisotropy and the other between the tidal anisotropy and the large-scale bias. We then use the Separate Universe technique to calibrate for the dependence of linear and quadratic halo bias on the tidal anisotropy as well as several other halo properties. Our calibration of the quadratic assembly bias is the first demonstration of the dependence of non-linear bias on the local web environment. Finally, we also describe an algorithm which makes use of the information in the cosmic web environment to increase the accessible dynamic range of large-volume simulations by an order of magnitude in halo mass.