A LOFAR-uGMRT spectral index study of distant radio halos

Abstract

Context. Radio halos are megaparsec-scale diffuse radio sources{ mostly} located at the centres of merging galaxy clusters. The common mechanism invoked to explain their origin is the re-acceleration of relativistic particles caused by large-scale turbulence. Aims. Current re-acceleration models predict that a significant number of halos at high redshift should be characterised by very steep spectra ($\alpha <-1.5$) because of increasing inverse Compton energy losses. In this paper, we investigate the spectral index properties of a sample of nine clusters selected from the second Planck Sunyaev-Zel'dovich catalogue showing diffuse radio emission with the Low Frequency Array (LOFAR) in the 120-168 MHz band. This is the first time that radio halos discovered at low frequencies are followed up at higher frequencies. Methods. We analysed upgraded Giant Metrewave Radio Telescope (uGMRT) observations in Bands 3 and 4, that is, 250-500 and 550-900 MHz respectively. These observations were combined with existing LOFAR data to obtain information on the spectral properties of the diffuse radio emission. Results. We find diffuse radio emission in the uGMRT observations for five of the nine high-$z$ radio halos previously discovered with LOFAR. For those, we measure spectral indices in the range of $-1$ to $-1.4$. For the uGMRT non-detections, we estimated that the halos should have a spectral index steeper than $-1.5$. We also confirm the presence of one candidate relic. Conclusions. Despite the small number of clusters, we find evidence that about half of the massive and merging clusters at high redshift host radio halos with a very steep spectrum. This is in line with theoretical predictions, although larger statistical samples are necessary to test models.

23 pages, 22 figures, 4 tables; accepted for publication in A&A

References in corpus (34)

• WSClean: an implementation of a fast, generic wide-field imager for radio astronomy
• The LOFAR Two-metre Sky Survey - I. Survey Description and Preliminary Data Release
• Diffuse Radio Emission from Galaxy Clusters
• eROSITA Science Book: Mapping the Structure of the Energetic Universe
• Particle Acceleration on Megaparsec Scales in a Merging Galaxy Cluster
• Compressible Turbulence in Galaxy Clusters: Physics and Stochastic Particle Re-acceleration
• On the connection between giant radio halos and cluster mergers
• An optimized algorithm for multi-scale wideband deconvolution of radio astronomical images
• The LOFAR Two Meter Sky Survey: Deep Fields, I -- Direction-dependent calibration and imaging
• Radio interferometric gain calibration as a complex optimization problem
• GMRT Radio Halo Survey in galaxy clusters at z = 0.2 -- 0.4. II.The eBCS clusters and analysis of the complete sample
• The Case for Electron Re-Acceleration at Galaxy Cluster Shocks
• GMRT Radio Halo Survey in galaxy clusters at z = 0.2 -- 0.4 I.The REFLEX sub--sample
• Statistics of Giant Radio Halos from Electron Reacceleration Models
• The intracluster magnetic field power spectrum in Abell 2255
• Shock acceleration as origin of the radio relic in A521?
• Non-linear Kalman filters for calibration in radio interferometry
• Turbulence and Particle Acceleration in Giant Radio Haloes: the Origin of Seed Electrons
• Relativistic protons in the Coma galaxy cluster: first gamma-ray constraints ever on turbulent reacceleration
• The Extended GMRT Radio Halo Survey II: Further results and analysis of the full sample
• Deep VLA observations of the cluster 1RXS J0603.3+4214 in the frequency range 1-2 GHz
• Deep LOFAR observations of the merging galaxy cluster CIZA J2242.8+5301
• Radio halos in a mass-selected sample of 75 galaxy clusters. II. Statistical analysis
• VLA Radio Observations of the HST Frontier Fields Cluster Abell 2744: The Discovery of New Radio Relics
• Fast magnetic field amplification in distant galaxyclusters
• On the absence of radio halos in clusters with double relics
• Analytical model for cluster radio relics
• Downstream depolarization in the Sausage relic: a 1-4 GHz Very Large Array study
• Evidence for a merger induced shock wave in ZwCl\,0008.8+5215 with {\it Chandra} and {\it Suzaku}
• Diffuse Radio Emission from Galaxy Clusters in the LOFAR Two-metre Sky Survey Deep Fields
• MERGHERS Pilot: MeerKAT discovery of diffuse emission in nine massive Sunyaev-Zel'dovich-selected galaxy clusters from ACT
• Diffuse Radio Sources in a Statistically Complete Sample of High Redshift Galaxy Clusters
• Diffuse radio emission in MACS J0025.4$-$1222: the effect of a major merger on bulk separation of ICM components
• Complex diffuse emission in the $z=0.52$ cluster PLCK~G004.5-19.5

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