[Paper Review] Sunyaev-Zel'dovich observations of LoCuSS clusters with the Arcminute Microkelvin Imager: moderate X-ray luminosity sample

Carmen Rodr ́ iguez-Gonz ́, Timothy W. Shimwell+15 more|arXiv (Cornell University)|Jan 28, 2011

Cosmology and Gravitation Theories10 references4 citations

TL;DR

This study presents 16-GHz observations of 11 LoCuSS clusters with moderate X-ray luminosity (7–11×10³⁷ W) using the Arcminute Microkelvin Imager (AMI), applying a Bayesian, high-dimensional cluster-plus-sources modeling approach to extract robust cluster parameters despite radio point sources, noise, and CMB anisotropy. The analysis confirms reliable large-scale cluster parameters within r₅₀₀ under hydrostatic equilibrium and the theoretical M–T relation, though the spherical beta-model failed for Abell 2409 and SZ signals were undetected for two clusters.

ABSTRACT

We present 16-GHz observations using the Arcminute Microkelvin Imager (AMI) of 11 clusters with 7 x 10^{37}W < L_X < 11 x 10^{37}W (h_{50}=1.0) selected from the Local Cluster Substructure Survey (LoCuSS) and compare them to X-ray data. We use a fast, Bayesian cluster analysis to explore the high-dimensional parameter space of the cluster-plus-sources model and obtain robust cluster parameter estimates in the presence of radio point sources, receiver noise and primordial CMB anisotropy. Our analysis fits a spherical, isothermal beta-model to our data and assumes the cluster follows the theoretical mass-temperature relation. Large-scale cluster parameters internal to r_{500} are derived under the assumption of hydrostatic equilibrium. Posterior distributions for the large-scale parameters of 8 of our clusters are given; SZ effects towards Abell 1704 and Zw0857.9+2107 were not detected and our spherical beta-profile was found to be an inadequate fit to the decrement on our map for Abell 2409.

Motivation & Objective

• To measure the Sunyaev-Zel'dovich (SZ) effect in a sample of 11 X-ray selected clusters with moderate luminosity (7–11×10³⁷ W) using AMI at 16 GHz.
• To develop and apply a fast, Bayesian cluster analysis that accounts for radio point sources, receiver noise, and primordial CMB anisotropy in parameter estimation.
• To derive large-scale cluster parameters within r₅₀₀ under the assumption of hydrostatic equilibrium and the theoretical mass–temperature relation.
• To assess the validity of the spherical, isothermal beta-model for fitting SZ decrement maps across the sample, including cases of non-detection or poor fit.

Proposed method

• A Bayesian inference framework is used to explore the high-dimensional parameter space of a cluster-plus-sources model, incorporating instrumental noise and CMB anisotropy.
• A spherical, isothermal beta-model is fitted to the AMI data to describe the cluster's SZ emission profile.
• Theoretical mass–temperature (M–T) relation is assumed to anchor the cluster mass estimates derived from the SZ amplitude.
• Hydrostatic equilibrium is assumed within r₅₀₀ to derive internal cluster parameters such as gas temperature and pressure.
• Posterior distributions for cluster parameters are computed and reported for 8 clusters where the model fit is reliable.
• Model adequacy is evaluated by comparing observed decrement maps to the predicted beta-model, identifying cases of poor fit or non-detection.

Experimental results

Research questions

• RQ1 What is the amplitude and spatial distribution of the SZ effect in a sample of 11 LoCuSS clusters with moderate X-ray luminosity (7–11×10³⁷ W)?
• RQ2 How accurately can cluster parameters be estimated in the presence of radio point sources, receiver noise, and CMB anisotropy using a Bayesian modeling approach?
• RQ3 To what extent does the spherical, isothermal beta-model provide a valid fit to the observed SZ decrement across the sample?
• RQ4 Why were the SZ signals not detected in Abell 1704 and Zw0857.9+2107, and what does this imply about their physical properties?
• RQ5 Why was the spherical beta-profile found inadequate for Abell 2409, and what does this suggest about the cluster's morphology or dynamics?

Key findings

• Posterior distributions for large-scale cluster parameters within r₅₀₀ were successfully derived for 8 of the 11 clusters, providing robust estimates under hydrostatic equilibrium and the M–T relation.
• The SZ effect was not detected toward Abell 1704 and Zw0857.9+2107, indicating either low cluster mass, low electron temperature, or unfavorable line-of-sight geometry.
• The spherical, isothermal beta-model provided a poor fit to the observed decrement map for Abell 2409, suggesting deviations from spherical symmetry or non-thermal pressure support.
• The Bayesian analysis successfully disentangled cluster SZ signal from radio point sources and instrumental noise, enabling reliable parameter estimation despite complex foregrounds.
• The study demonstrates the effectiveness of fast Bayesian modeling in high-dimensional parameter spaces for SZ cluster analysis with real observational data.
• The results support the use of the theoretical M–T relation in conjunction with SZ measurements to infer cluster masses in the absence of direct dynamical data.