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Effects of Mergers and Dynamical Sta...

Nelson, Katherine Lea.

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Effects of Mergers and Dynamical State on Galaxy Clusters in Cosmological Simulations.

Record Type:	Electronic resources : Monograph/item
Title/Author:	Effects of Mergers and Dynamical State on Galaxy Clusters in Cosmological Simulations./
Author:	Nelson, Katherine Lea.
Description:	163 p.
Notes:	Source: Dissertation Abstracts International, Volume: 77-06(E), Section: B.
Contained By:	Dissertation Abstracts International77-06B(E).
Subject:	Astrophysics. -
Online resource:	http://pqdd.sinica.edu.tw/twdaoapp/servlet/advanced?query=10010358
ISBN:	9781339464084

Effects of Mergers and Dynamical State on Galaxy Clusters in Cosmological Simulations.
Nelson, Katherine Lea.

Effects of Mergers and Dynamical State on Galaxy Clusters in Cosmological Simulations. - 163 p.

Source: Dissertation Abstracts International, Volume: 77-06(E), Section: B.

Thesis (Ph.D.)--Yale University, 2015.

Galaxy clusters are the largest gravitationally bound objects in the Universe. Their deep potential wells provide excellent laboratories for detailed examination of the matter content of the Universe. Their abundance as a function of mass and redshift is also sensitive to the growth rate of density perturbations as well as the expansion rate of the Universe. Hot gas in groups and clusters of galaxies also leave fluctuation patterns in the X-ray and microwave skies. Recent and ongoing surveys in the X-ray and microwave wavelengths are supplying unprecedented large samples of galaxy clusters in an attempt to realize this potential. However, our ability to harness clusters as cosmological probes is principally limited by the accuracy with which their total mass can be measured. The most widely used mass estimate techniques, such as the hydrostatic mass estimate and SunyaevZeldovich (SZ) scaling relation, are potentially biased by non-thermal pressure from gas motions in the intracluster medium. In this dissertation, we use cosmological hydrodynamic simulations to examine the origin and evolution of gas motions and the resulting non-thermal pressure in galaxy clusters and their effect on the mass estimates critical for utilizing clusters as cosmological probes.

ISBN: 9781339464084Subjects--Topical Terms:

535904
Astrophysics.

Effects of Mergers and Dynamical State on Galaxy Clusters in Cosmological Simulations.
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100 1 $a Nelson, Katherine Lea. $3 3192591
245 1 0 $a Effects of Mergers and Dynamical State on Galaxy Clusters in Cosmological Simulations.
300 $a 163 p.
500 $a Source: Dissertation Abstracts International, Volume: 77-06(E), Section: B.
500 $a Adviser: Daisuke Nagai.
502 $a Thesis (Ph.D.)--Yale University, 2015.
520 $a Galaxy clusters are the largest gravitationally bound objects in the Universe. Their deep potential wells provide excellent laboratories for detailed examination of the matter content of the Universe. Their abundance as a function of mass and redshift is also sensitive to the growth rate of density perturbations as well as the expansion rate of the Universe. Hot gas in groups and clusters of galaxies also leave fluctuation patterns in the X-ray and microwave skies. Recent and ongoing surveys in the X-ray and microwave wavelengths are supplying unprecedented large samples of galaxy clusters in an attempt to realize this potential. However, our ability to harness clusters as cosmological probes is principally limited by the accuracy with which their total mass can be measured. The most widely used mass estimate techniques, such as the hydrostatic mass estimate and SunyaevZeldovich (SZ) scaling relation, are potentially biased by non-thermal pressure from gas motions in the intracluster medium. In this dissertation, we use cosmological hydrodynamic simulations to examine the origin and evolution of gas motions and the resulting non-thermal pressure in galaxy clusters and their effect on the mass estimates critical for utilizing clusters as cosmological probes.
520 $a First, we examine the effects of major mergers and accretion history on the hydro-static mass estimate. We find that during a major merger, the hydrostatic mass estimate systematically underestimates the true mass. Mergers generate a large amount of gas velocities, supplying unaccounted for non-thermal pressure, which can supply as much as a third of the total pressure support in the intracluster medium. While the non-thermal pressure fraction and therefore the mass bias decreased with time since the merging event, we find a non-zero residual non-thermal pressure fraction and mass bias, even in relaxed clusters. Moreover, until recently, all attempts to account for non-thermal pressure in galaxy clusters have assumed that net gas velocity is constant with time and therefore that gas accelerations provide no contribution to non-thermal pressure support. Therefore, we also examine the effects of dynamical state on the mass bias in galaxy clusters in the presence of gas acceleration in the intracluster medium. We find that for relaxed systems, the contribution to the mass bias from acceleration is small and can be well accounted for in the simulation. However, for unrelaxed clusters, the gas accelerations can be large and present an irreducible bias in the hydrostatic mass estimate.
520 $a Despite the important role of gas motions in cluster astrophysics and cosmology, we know very little about them observationally. We therefore use our simulation to model the non-thermal pressure fraction profile. We find that the non-thermal pressure fraction profile exhibits an approximately universal form when normalized with respect to the mean density of the universe. However, we further find that unrelaxed galaxy clusters have systematically higher non-thermal pressure fraction than relaxed clusters. We propose a fitting formula for the non-thermal pressure fraction profile which takes into account the dependence on the mass accretion rate. Lastly, we characterize the effect of dynamical state on the SZ scaling relation, which exhibits a tight relation between the SZ signal (Ysz) and mass and holds a key for deriving robust cosmological constraints from cluster surveys. We find that merger-induced gas motions play a dominant role in setting the size of the scatter in this relation. Moreover, when we account for non-thermal pressure support in the galaxy clusters and their dynamical state, the scatter of the relation is reduced by almost a factor of 2. Our work opens up a possibility to further improve the current robust mass proxy, Y sz, by accounting for the missing non-thermal pressure component.
520 $a We conclude by discussing possible observational avenues for measuring gas motions. We also outline the next steps and future work in simulations for further characterization of the non-thermal pressure contribution in the ICM.
590 $a School code: 0265.
650 4 $a Astrophysics. $3 535904
690 $a 0596
710 2 $a Yale University. $3 515640
773 0 $t Dissertation Abstracts International $g 77-06B(E).
790 $a 0265
791 $a Ph.D.
792 $a 2015
793 $a English
856 4 0 $u http://pqdd.sinica.edu.tw/twdaoapp/servlet/advanced?query=10010358