Research

Table of Contents

Introduction

research word cloud

This page aims to give a quick overview of the things I've worked on in grad school. If you want less detail, check out the "word cloud" visualization of my papers above; if you want more detail, you can browse my publications here.

Convection in Galaxy Clusters

buoyancy saturation poster

The plasma in galaxy clusters is magnetized, weakly collisional, and thermally conductive. Together, these properties significantly modify the physics of convection. Though clusters had long been assumed to be stable to convection, it now seems that the intracluster plasma probably boils.

I've worked a bit on this convection, in particular toward understanding the non-linear saturation of the convective instabilities. The net effect appears to be that magnetic field lines wrap up near the centers of clusters, and that convection drives turbulence in the outskirts. The magnitude of these effects is still uncertain, but it is probably a non-monotonic function of mass.

For more information, check out the poster above (click for a bigger file), or see my paper.

Thermal Instability

thermal instability poster

I've also studied thermal instability in galaxy clusters. Whether or not the plasma in clusters is thermally unstable is a surprisingly tricky question — it depends on the unknown "feedback" process heating the plasma.

Under the reasonable assumption that the plasma in clusters is thermally unstable, however, the non-linear saturation turns out to have an interesting result: the instability can only grow to large amplitudes at special locations in the cluster. This location coincides with the "filaments" of cold gas seen in many clusters, and it offers a quantitative explanation of the x-ray luminosity-temperature relation.

Check out the poster above (click for a larger image), or see this paper and this paper for more details.

Structure Formation and Cluster Outskirts

outer parts poster

Somehow, clusters maintain their large-scale temperature gradients in spite of thermal conduction and convection.

The work described in the poster to the right (and in this paper) argues that the continued formation of clusters actually generates and maintains this temperature gradient. Measuring the properties of the gas in clusters may thus directly constrain for formation histories of clusters.

The paper also outlines a method for using the (known) scatter in accretion histories to predict the (unknown) scatter in cluster observables. My collaborators and I are currently using this method to better understand potential biases in some cosmological measurements.

Date: 2013-10-07T11:14-0700

Author: Michael McCourt

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