Micro-Calorimeter X-Ray Spectroscopy of Galaxy Clusters using the XRISM X-Ray Observatory

Abstract

Galaxy clusters are some of the most massive objects in the universe, yet the evolution of these objects, particularly with regards to the heating and cooling of the intracluster medium, still has many unknowns. With the launch of the new X-ray imaging and spectroscopy mission, XRISM, galaxy clusters can now be studied with higher precision. This data can reveal a plethora of new information about the dynamics of the atmospheres of these clusters, which can be used to develop a better understanding of the evolution of galaxy clusters.

In this thesis, I present analysis of X-ray spectroscopic data of the Perseus, Hydra A, and Cygnus A clusters obtained with XRISM Resolve. We apply spectral modeling techniques to the data to derive gas temperature, metal abundance, velocity dispersion, and bulk velocity to develop a further understanding of the dynamics of the intracluster medium in these galaxy clusters.

I present spectral analysis of the five XRISM Resolve pointings of the Perseus cluster, binned into a radial profile. We measure radial profiles of temperature, metal abundances, velocity dispersion, and bulk velocities up to $\sim250$ kpc from the cluster center with single temperature models. While the temperature and abundance profiles are consistent with typical cool core clusters, the velocity dispersions suggest a relatively quiescent state for the intracluster medium, with only up to $\sim175$ km s$^{-1}$ dispersion in the central $\sim 60$ kpc. We interpret this velocity dispersion to be due to turbulence. The dispersion profile suggests that the jets and bubbles may be driving turbulence in the core, but also that the core may be under-heated. We find evidence for a second temperature component in the inner $\sim60$ kpc, that is cooler ($\sim2-2.4$ keV) and has a significantly higher velocity dispersion of $\sim300-400$ km s$^{-1}$. We interpret the cooler component to be sloshing gas from a merger or gas being churned by the jets and bubbles.

I present spectral analysis of the full-FOV XRISM Resolve data of the Hydra A cluster, measuring temperature, velocity dispersion, and bulk velocity with a single temperature model. Despite Hydra A's high jet power, we find a remarkably low velocity dispersion of $164^{+10}_{-10}$ km s$^{-1}$, and a small velocity offset of $-37^{+20}_{-17}$ km s$^{-1}$ between the gas and the central galaxy. We interpret this velocity dispersion to be due to turbulence, which may suggest that the relationship between the jet power and the velocity structure of the intracluster medium is less significant than expected. However, further analysis of the outer regions of the cluster is needed to fully understand the dynamics of the gas in Hydra A.

Finally, I present spectral analysis of the full-FOV XRISM Resolve data of the Cygnus A cluster, measuring temperature, metal abundances, velocity dispersion, and bulk velocity with a single temperature model. We measure a relatively higher velocity dispersion of $272^{+14}_{-13}$ km s$^{-1}$ with a bulk velocity of $101\pm26$ km s$^{-1}$ with respect to the central galaxy. These velocities likely reflect a combination of both turbulence in the gas and motion of the cocoon shock. We find some evidence for a second temperature component, that is cooler ($2.06^{+0.43}_{-0.20}$ keV) and broader ($333^{+127}_{-129}$ km s$^{-1}$), with a bulk velocity of $-311\pm118$ km s$^{-1}$. The second component may be necessary for fitting asymmetric features in the prominent emission lines of the spectrum. However, the large uncertainties of the model fit along with other uncertainties suggest that this component may not be significant.