[Paper Review] The Evolution of Galaxy Clusters Across Cosmic Time

M. Arnaud, H. Böhringer+41 more|ArXiv.org|Feb 27, 2009

Cosmology and Gravitation Theories2 references3 citations

TL;DR

This paper proposes that high-throughput, high-resolution X-ray observations—particularly from the proposed IXO mission—are essential to unravel the cosmic evolution of galaxy clusters, focusing on baryonic dynamics, metal enrichment, and nonthermal processes. By mapping thermodynamic properties, metallicity distributions, and relativistic particle emissions across cosmic time, the study aims to resolve how energy, metals, and turbulence evolve in dark matter potentials.

ABSTRACT

The large scale structure of the present Universe is determined by the growth of dark matter density fluctuations and by the dynamical action of dark energy and dark matter. While much progress has been made in recent years in constraining the cosmological parameters, and in reconstructing the evolution in the large--scale structure of the dark matter distribution, we still lack an understanding of the evolution of the baryonic component of the Universe. Located at nodes of the cosmic web, clusters of galaxies are the largest collapsed structures in the Universe with total masses up to 10$^{15}$ M$_{\sun}$. Over 80% of their mass resides in the form of dark matter. The remaining mass is composed of baryons, most of which (about 85%) is a diffuse, hot plasma that radiates primarily in X-rays. X-ray observations of the evolving cluster population provide a unique opportunity to address such open and fundamental questions as: How do hot diffuse baryons dynamically evolve in dark matter potentials? How and when was the excess energy which we observe in the intergalactic medium generated? What is the cosmic history of heavy-element production and circulation? Our current knowledge comes primarily from detailed studies of clusters in the relatively nearby Universe (z$

Motivation & Objective

• To understand the dynamical evolution of hot baryonic gas within dark matter potentials in galaxy clusters.
• To determine the origin and evolution of excess energy in the intracluster medium (ICM), including heating, turbulence, and bulk motions.
• To trace the cosmic history of metal production and redistribution in the ICM, particularly through galactic winds and ram pressure stripping.
• To measure nonthermal pressure support from relativistic particles and shocks in merging clusters.
• To improve cosmological constraints by refining cluster mass measurements through accurate modeling of baryonic and nonthermal components.

Proposed method

• Utilize high-throughput, high-resolution X-ray spectroscopy to map the thermodynamic state of the intracluster medium (ICM) across redshifts up to z ~ 2.
• Apply spatially resolved X-ray spectroscopy with calorimeter instruments to measure metallicity distributions and abundance patterns, including trace elements like Mn and Cr.
• Combine X-ray data with multi-wavelength observations (optical, IR, radio) to study galaxy feedback, ram pressure stripping, and AGN outflows.
• Use deep X-ray exposures (e.g., ~100 ksec for z=0.1 clusters) to map ICM properties over scales of ~0.5 Mpc with high signal-to-noise.
• Model the ICM using multi-phase hydrodynamics and feedback prescriptions, informed by observational constraints from IXO and other telescopes.
• Incorporate gravitational lensing and radio synchrotron emission data to trace dark matter and relativistic particle populations.

Experimental results

Research questions

• RQ1 How does gravitational energy released during hierarchical cluster assembly heat the ICM and drive turbulence and bulk motions?
• RQ2 What are the acceleration mechanisms and origins of relativistic particles observed in the ICM, particularly in shock fronts and turbulent regions?
• RQ3 How do metallicity distributions in the ICM evolve over cosmic time, and what processes—galactic winds, ram pressure stripping, or AGN outflows—dominate metal enrichment?
• RQ4 To what extent does nonthermal pressure support affect cluster mass measurements, and how does it evolve with redshift and dynamical state?
• RQ5 How do abundance patterns of trace elements (e.g., Mn, Cr) constrain the cosmic history of Type Ia supernova enrichment in clusters?

Key findings

• High-resolution X-ray spectroscopy with IXO will enable metallicity mapping in low-mass clusters up to z ~ 2, resolving spatial inhomogeneities in the ICM.
• Element abundance profiles can be measured up to z ~ 1 in poor clusters and z ~ 2 in massive clusters, providing constraints on the cosmic history of nucleosynthesis.
• The 2D metallicity distribution in nearby clusters can be resolved down to physical mixing scales, allowing direct study of metal injection from ram pressure stripped tails (e.g., M86).
• Trace elements like Mn and Cr can be measured in a significant number of clusters, offering new constraints on the metallicity of SNe Ia progenitors.
• Nonuniform metallicity assumptions lead to underestimation of true metal mass in clusters, highlighting the need for spatially resolved abundance measurements.
• IXO’s high energy resolution will allow detection of velocity fields and turbulence in the ICM, directly probing the dynamics of hot gas in cluster mergers.