The effect of environment in simulated galaxy clusters
Publication Date
December 13, 2019
Creator
Abstract
In this Thesis, we predominately study the effect of environment on infalling galax- ies in hydrodynamical galaxy cluster zoom simulations. Our studies focus both within the virial radius of the galaxy cluster, and outside of it in the infall region; a relatively untapped region of scientific study. In order to study the effects of environ- ment within these simulations, we monitor the gaseous properties of (sub)haloes in combination with environmental quenching mechanisms, which are principally ram pressure stripping and pre-processing. The dataset we use to achieve these goals is the TheThreeHundred project; a suite of 324 resimulated massive galaxy clusters embedded in a broad range of environments. Before attention is directed towards these objectives, however, we lay the foundations of this Thesis by carrying out an investigation into what components and calibration schemes hydrodynamical codes need to use in order to simulate realistic galaxy clusters. This is done with the nIFTy cluster comparison project, a precursor to TheThreeHundred.
We firstly study the properties of the galaxies and (sub)haloes residing in the cluster infall region surrounding the simulated nIFTy galaxy cluster at z = 0. The 1.1 × 10^15 h−1 M⊙ galaxy cluster has been simulated with eight different hydrody- namical codes containing a variety of hydrodynamic gas solvers and subgrid schemes. We find that the codes produced widely varying numbers of (sub)haloes and galaxies with a large range of masses; in the more extreme cases, some codes even produced a factor of 20 more galaxies than others. Our evidence strongly supports that the dif- ferent subgrid physics used by each code dominates this code-to-code scatter, after a control on local object environment has been enforced. By comparing the stel- lar fractions of (sub)haloes to halo abundance matching trends, we showed that the same codes under and overproduced stars in every (sub)halo mass bin. In particular, codes that didn’t include some form of AGN feedback produced the most unrealistic, overly stellar rich set of objects. The basis of these results helped to identify which of the included codes would be most suitable for running the TheThreeHundred clusters.
We next turn towards the effects of environment in cluster simulations, by using TheThreeHundred project to investigate (i) how the gas content of surrounding (sub)haloes correlates with phase-space position at z = 0, and (ii) to investigate the role that ram pressure plays in this correlation. By stacking all 324 normalised phase-space planes containing 169 238 haloes and subhaloes, we show that the halo gas content is tightly correlated with phase-space position. At ∼ 1.5 − 2 R200 of the cluster dark matter halo, we find an extremely steep decline in the halo gas content of infalling haloes and subhaloes irrespective of cluster mass, possibly indicating the presence of an accretion shock. We also find that subhaloes are particularly gas-poor, even in the cluster outskirts, which could indicate active regions of ongoing pre- processing. By modelling the instantaneous ram pressure experienced by each halo and subhalo at z = 0, we show that the ram pressure intensity is also well correlated with phase-space position, which is again irrespective of cluster mass. In fact, we show that regions in the phase-space plane with high differential velocity between a halo or subhalo and its local gas environment, are almost mutually exclusive with high halo gas content regions. This suggests a causal link between the gas content of objects and the instantaneous ram pressure they experience, where the dominant factor is the differential velocity.
These results are directly extended by investigating the level of gaseous disrup- tion of infalling objects and the extent of pre-processing in TheThreeHundred, by utilising temporal information. We use the orbital histories of the same set of 169238 (sub)haloes to identify where, when and how these objects lose their gas since crossing 4 R200 into the infall region, which we define as the region encapsulat- ing 1 − 4 R200. We find that objects traversing this region suffer significant gaseous disruption, which is driven by a combination of (i) gas depletion of objects accreting onto a characteristic radius, and (ii) subhalo pre-processing by host environments. We find that infalling objects typically lose nearly all of their gas by ∼ 1.7 R200 (in real space) and ∼ 1 R200 (in projected space), and it is likely that this is happening on first infall. Alongside this, we also show that subhaloes lose their gas at both higher cluster-centric distances and sooner after infall than haloes. We show that this is likely driven by pre-processing in host environments, as subhaloes are gas depleted much sooner in higher mass hosts than in low mass hosts.
Item Type
ethesis
Thesis Type
PhD
Supervisors
Subjects (LC)
Associated Schools / Departments
School of Physics and Astronomy
eprints ID
57075
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