ALMA-SZ Detection of a Galaxy Cluster Merger Shock at Half the Age of the Universe

Abstract

We present ALMA measurements of a merger shock using the thermal Sunyaev-Zel'dovich (SZ) effect signal, at the location of a radio relic in the famous El Gordo galaxy cluster at $z\approx 0.9$. Multi-wavelength analysis in combination with the archival Chandra data and a high-resolution radio image provides a consistent picture of the thermal and non-thermal signal variation across the shock front and helps to put robust constraints on the shock Mach number as well as the relic magnetic field. We employ a Bayesian analysis technique for modeling the SZ and X-ray data self-consistently, illustrating respective parameter degeneracies. Combined results indicate a shock with Mach number $\mathcal{M}=2.4_{-0.6}^{+1.3}$, which in turn suggests a high value of the magnetic field (of the order of $4-10\mu$G) to account for the observed relic width at 2 GHz. At roughly half the current age of the universe, this is the highest-redshift direct detection of a cluster shock to date, and one of the first instances of an ALMA-SZ observation in a galaxy cluster. It shows the tremendous potential for future ALMA-SZ observations to detect merger shocks and other cluster substructures out to the highest redshifts.

Matched to the ApJL published version (2016 September 22), minor grammar and typo fixes

References in corpus (5)

• Particle Acceleration on Megaparsec Scales in a Merging Galaxy Cluster
• The Atacama Cosmology Telescope: Physical Properties and Purity of a Galaxy Cluster Sample Selected via the Sunyaev-Zel'dovich Effect
• A $\mathcal{M}\gtrsim 3$ shock in `El Gordo' cluster and the origin of the radio relic
• A Hydrodynamical Solution for the "Twin-Tailed" Colliding Galaxy Cluster "El Gordo"
• Evidence for a pressure discontinuity at the position of the Coma relic from Planck Sunyaev-Zel'dovich effect data

Cited by in corpus (16)

• Diffuse Radio Emission from Galaxy Clusters
• Exploring the spectral properties of radio relics I: Integrated spectral index and Mach number
• Wideband 67-116 GHz receiver development for ALMA Band 2
• Electron Heating in Low Mach Number Perpendicular shocks. I. Heating Mechanism
• Head-to-Toe Measurement of El Gordo: Improved Analysis of the Galaxy Cluster ACT-CL J0102-4915 with New Wide-field Hubble Space Telescope Imaging Data
• Shocks in the Stacked Sunyaev-Zel'dovich Profiles of Clusters I: Analysis with the Three Hundred Simulations
• Shocks in the Stacked Sunyaev-Zel'dovich Profiles of Clusters II: Measurements from SPT-SZ + Planck Compton-y Map
• A MUSE view of the massive merging galaxy cluster ACT-CL J0102-4915 (El Gordo) at z = 0.87: robust strong lensing model and data release
• Multiwavelength view of SPT-CL J2106-5844. The radio galaxies and the thermal and relativistic plasmas in a massive galaxy cluster merger at z~1.13
• CMB-HD: Astro2020 RFI Response
• The velocity structure of the intracluster medium during a major merger: simulated microcalorimeter observations
• The Massive and Distant Clusters of WISE Survey: SZ effect Verification with the Atacama Compact Array -- Localization and Cluster Analysis
• Galaxy clusters at z~1 imaged by ALMA with the Sunyaev-Zel'dovich effect
• Atacama Large Aperture Submillimeter Telescope (AtLAST) Science: Resolving the Hot and Ionized Universe through the Sunyaev-Zeldovich effect
• A High-resolution SZ View of the Warm-Hot Universe
• Thermal Sunyaev-Zel'dovich effect at the core of CL J1226.9+3332 revealed by NOEMA