arXiv subjects

Peter A. Thomas

Publications and source records attributed to Peter A. Thomas.

76 records · Page 5Linked to original sources

arXiv1997

The structure of galaxy clusters in different cosmologies

We investigate the internal structure of clusters of galaxies in high-resolution N-body simulations of 4 different cosmologies. There is a higher proportion of disordered clusters in critical-density than in low-density universes, although the structure of relaxed clusters is very similar in each. Crude measures of substructure, such as the shift in the position of the centre-of-mass as the density threshold is varied, can distinguish the two in a sample of just 20 or so clusters; it is harder to differentiate between clusters in open and flat models with the same density parameter. Most clusters are in a quasi-steady state within the virial radius and are well-described by the density profile of Navarro, Frenk & White (1995).

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arXiv1996

Mass constraints from multiphase cooling flow models

I review the multiphase cooling flow equations that reduce to a relatively simple form for a wide class of self-similar density distributions described by a single parameter, $k$. It is shown that steady-state cooling flows are \emph{not} consistent with all possible emissivity profiles which can therefore be used as a test of the theory. In combination, they provide strong constraints on the temperature profile and mass distribution within the cooling radius. The model is applied to ROSAT HRI data for 3 Abell clusters. At one extreme ($k\sim1$) these show evidence for cores in the mass distribution of size 110--140$ h_{50}^{-1}$kpc and have temperatures which decline towards the flow centre. At the other ($k\mapsto\infty$), the mass density and gas temperature both rise sharply towards the flow centre. The former are more consistent with measured temperatures, which suggests that the density distribution in the intracluster medium contains the minimum possible mixture of low-density components.

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arXiv1996

Multiphase cooling flows

I discuss the multiphase nature of the intracluster medium whose neglect can lead to overestimates of the baryon fraction of clusters by up to a factor of two. The multiphase form of the cooling flow equations are derived and reduced to a simple form for a wide class of self-similar density distributions. It is shown that steady-state cooling flows are \emph{not} consistent with all possible emissivity profiles which can therefore be used as a test of the theory. In combination, they provide strong constraints on the mass distribution within the cooling radius.

astro-ph↗

arXiv1995

Merger trees and the multiplicity function of halos

We present a new method for calculating the merger history of matter halos in hierarchical clustering cosmologies. The linear density field is smoothed on a range of scales, these are then ordered in decreasing density and a merger tree constructed. The method is similar in many respects to the block model of Cole \& Kaiser but has a number of advantages: (i) it retains information about the spatial correlations between halos, (ii) it uses a series of overlapping grids and is thereby much better at finding rare, high-mass halos, (iii) it is not limited to halos whose mass ratios are powers of two, and (iv) it is based on an actual realization of the density field and so can be tested against N-body simulations. The major disadvantages are (i) the minimum halo mass is eight times the unit cell with a corresponding loss of dynamic range, and (ii) occasionally the relative location of halos in the tree does not reflect the correct ordering of their collapse times, as computed from the mean halo density. We show that our model exhibits the required scaling behaviour when tested on power-law spectra of density perturbations, but that it predicts far more massive halos than does the Press-Schechter formalism for flat spectra. We suggest reasons why this should be so.

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