[Paper Review] Towards the 2020 vision of the baryon content of galaxy groups and clusters

Andrey V. Kravtsov, Anthony H. Gonzalez+13 more|ArXiv.org|Mar 2, 2009

Astronomy and Astrophysical Research1 references5 citations

TL;DR

This white paper proposes a multi-wavelength observational and theoretical campaign to measure the baryon content of galaxy groups and clusters across cosmic time, focusing on radial distributions of stars, hot gas, cold gas, and dark matter. By combining X-ray, SZ, ALMA, and lensing data with advanced simulations, it aims to constrain galaxy formation models and feedback mechanisms, ultimately improving cosmological constraints from cluster mass fractions.

ABSTRACT

Groups and clusters of galaxies occupy a special position in the hierarchy of large-scale cosmic structures because they are the largest and the most massive (from ~10^13 Msun to over 10^15 Msun) objects in the universe that have had time to undergo gravitational collapse. The large masses of clusters imply that their contents have been accreted from regions of ~8-40 comoving Mpc in size and should thus be representative of the mean matter content of the universe. During the next decade sensitive multi-wavelength observations should be able to map the radial distributions of all main mass components (stars, cold, warm, and hot gas and total mass) at z

Motivation & Objective

• To determine whether the baryon fraction in galaxy groups and clusters reflects the cosmic mean within observable radii.
• To map the radial distributions of stars, cold gas, hot gas, and dark matter in clusters across redshifts.
• To use cluster baryon budgets to constrain galaxy formation and feedback models, including AGN and stellar feedback.
• To improve cosmological constraints by measuring the evolution of hot gas and stellar mass fractions with redshift.
• To calibrate mass estimates from hydrostatic equilibrium using strong and weak lensing as independent checks.

Proposed method

• Combine X-ray observations of ICM temperature and density profiles with Sunyaev-Zel'dovich (SZ) measurements to derive total mass profiles in relaxed clusters.
• Use ALMA and SKA pathfinder missions to map molecular and atomic cold gas in cluster centers and outskirts.
• Apply strong and weak gravitational lensing from space-based and ground-based wide-field imaging to measure total mass independently.
• Employ adaptive mesh refinement and Lagrangian techniques in cosmological simulations to resolve kpc-scale processes in cluster centers.
• Cross-check mass profiles from X-ray and SZ data with lensing measurements to identify systematic biases in hydrostatic equilibrium assumptions.
• Use statistical samples of cluster arcs and lensing shear from wide-area surveys to calibrate mass estimates and test feedback models.

Experimental results

Research questions

• RQ1 Does the baryon fraction in groups and clusters match the cosmic mean within the virial radius?
• RQ2 What are the radial profiles of stars, cold gas, hot gas, and dark matter in clusters at different redshifts?
• RQ3 How do observed baryon fractions constrain the efficiency of star formation and feedback in galaxy formation?
• RQ4 To what extent do deviations from hydrostatic equilibrium affect mass measurements in cluster outskirts?
• RQ5 How do plasma effects such as helium sedimentation influence the observed baryon distribution in clusters?

Key findings

• Accurate X-ray and SZ measurements of gas density and temperature profiles will enable robust total mass reconstruction for hundreds of relaxed clusters across redshifts.
• ALMA will enable high-sensitivity mapping of molecular gas in cluster cores at multiple redshifts, revealing the extent of cooling and feedback.
• HI mapping with SKA pathfinder missions will trace diffuse atomic gas in distant clusters, improving cold gas budget estimates.
• Strong and weak lensing measurements from wide-field surveys will provide independent mass profiles, reducing reliance on hydrostatic equilibrium assumptions.
• Simulations with adaptive resolution will resolve kpc-scale structures like cold fronts and turbulence, improving modeling of feedback and non-thermal effects.
• Cross-checking X-ray, SZ, and lensing mass profiles will help identify and correct for systematic errors in baryon fraction measurements.