The Role of Baryons and Neutrinos in the Evolution of Large-Scale Structure

Galaxy groups and clusters (GGCs) hold a privileged position within the cosmological hierarchy. As the most recent structures to have formed, their abundances, spatial distribution and individual properties bear the indelible imprint of the background cosmology, initial conditions and their formation history, making them valuable probes of both cosmology and astrophysics. It has, however, become increasingly clear over the past decade that making use of these probes for precision cluster cosmology requires detailed, realistic predictions for the observed properties of GGCs. Producing these necessitates the use of large cosmological hydrodynamical simulations with realistic ‘sub-grid’ prescriptions for baryonic physics. One mechanism in need of addressing is the effect of the cosmic background of massive neutrinos. As these remain relativistic to relatively late times, they will free-stream out of overdensities, altering the formation of large-scale structure (LSS). If this effect can be accurately modelled, it presents an independent method of constraining the value of the neutrino mass by means of LSS observations. This thesis makes use of the cosmo-OWLS and BAHAMAS cosmological hydrodynamical simulation suites to explore the separate and combined effects of baryon physics (particularly feedback from active galactic nuclei, AGN) and the free-streaming of massive neutrinos on large-scale structure. I focus on five diagnostics: i) the halo mass function; ii) halo mass density profiles; iii) the halo mass concentration relation; iv) the clustering of haloes; and v) the clustering of matter; and I explore the extent to which the effects of baryon physics and neutrino free-streaming can be treated independently. In comparing to the GAMA observations, I find that these data provide insufficient statistical power to constrain the value of the summed neutrino mass. This is primarily due to the intrinsic scatter in the stellar mass - halo mass relation, and the strong dependence of the sensitivity on precise mass binning. As a consequence, more precise estimations of the halo mass will be required in future work seeking to utilise this metric. Finally, I find that the clustering of simulated BAHAMAS groups is remarkably consistent with that of observed GAMA groups. This lends additional weight to the argument that BAHAMAS accurately reproduces the properties of the GGC population, and supports its use as a cosmological tool.

Name dc:type.qualificationname

phd

Level dc:type.qualificationlevel

doctoral

Grantor dc:publisher.institution

Liverpool John Moores University

Year dc:date.issued

2018

Author dc:creator

• Mummery, BO

Contributors dc:contributor

• McCarthy, I

• QB Astronomy
• QC Physics