Resurging from the ashes: A spectral study of seven candidate revived radio fossils in nearby low-mass galaxy clusters

Abstract

Complex energy transfer processes in the intracluster medium (ICM) can revive fossil (with spectral ages $\gg 100$ Myr) plasma initially generated by radio galaxies. This leads to the re-ignition of faint radio sources with irregular and filamentary morphologies, and ultra-steep ($\alpha \gtrsim 1.5$) synchrotron spectra, which can be more easily detected at low frequencies ($\sim 100$ MHz). These sources offer the opportunity to investigate the microphysics of the ICM and its interplay with radio galaxies, the origin of seed relativistic electrons, the merging history of the host cluster, and the phenomenology of radio filaments. The study of revived sources has so far been hampered by the requirement of sensitive and high-resolution multi-frequency radio data at low frequencies to characterise their spatial properties and provide a proper classification. We aim to perform the analysis of a sample of candidate revived sources identified among nearby ($z\le 0.35$) and low-mass ($M_{500}\le 5\times 10^{14}{M}_{\odot }$) \textit{Planck} clusters in the footprint of LoTSS-DR2. By inspecting LoTSS-DR2 images at 144 MHz, we identified 7 targets with patchy and filamentary morphologies, which have been followed-up with the uGMRT at 400 MHz. By combining LOFAR and uGMRT data, we obtained high-resolution images and spectral index maps, which we used to interpret the nature of the sources. All targets show regions with very steep spectra, confirming the effectiveness of our morphology-based selection in identifying fossil plasma. Based on their morphology, spectral properties, and optical associations, we investigated the origin of the targets. We found a variety of promising revived fossil sources, while also showing that apparently intricate structures can be easily misclassified in the absence of high-resolution and multi-band data.

17 pages (12 main text + 5 appendix). Accepted for publication in A&A

References in corpus (38)

• Array Programming with NumPy
• WSClean: an implementation of a fast, generic wide-field imager for radio astronomy
• The LOFAR Two-metre Sky Survey -- V. Second data release
• On the connection between giant radio halos and cluster mergers
• An optimized algorithm for multi-scale wideband deconvolution of radio astronomical images
• The impact of mergers on relaxed X-ray clusters - I. Dynamical evolution and emergent transient structures
• Searching for Cool Core Clusters at High redshift
• Calibration of the optical mass proxy for clusters of galaxies and an update of the WHL12 cluster catalog
• LOFAR observations of galaxy clusters in HETDEX
• Gentle re-energisation of electrons in merging galaxy clusters
• The Planck clusters in the LOFAR sky. I. LoTSS-DR2: new detections and sample overview
• All-purpose, all-sky photometric redshifts for the Legacy Imaging Surveys Data Release 8
• Collimated synchrotron threads linking the radio lobes of ESO137-006
• Intracluster magnetic filaments and an encounter with a radio jet
• Revived Fossil Plasma Sources in Galaxy Clusters
• Unveiling the rarest morphologies of the LOFAR Two-metre Sky Survey radio source population with self-organised maps
• The Planck clusters in the LOFAR sky: IV: LoTSS-DR2: statistics of radio halos and re-acceleration models
• Threads, Ribbons, and Rings in the Radio Galaxy IC 4296
• How merger-driven gas motions in galaxy clusters can turn AGN bubbles into radio relics
• The galaxy group NGC 507: newly detected AGN remnant plasma transported by sloshing
• The Planck clusters in the LOFAR sky VI. LoTSS-DR2: Properties of radio relics
• Abell 1033: Radio halo and gently reenergized tail at 54 MHz
• Discovery of Peculiar Radio Morphologies with ASKAP using Unsupervised Machine Learning
• The Planck clusters in the LOFAR sky. III. LoTSS-DR2: Dynamic states and density fluctuations of the intracluster medium
• The great Kite in the sky: a LOFAR observation of the radio source in Abell 2626
• A LOFAR view into the stormy environment of the galaxy cluster 2A0335+096
• Particle re-acceleration and diffuse radio sources in the galaxy cluster Abell 1550
• High-resolution, High-sensitivity, Low-frequency uGMRT View of Coma Cluster of Galaxies
• NGC 4869 in the Coma cluster: twist, wrap, overlap and bend
• Populations of Magnetized Filaments in the Intracluster Medium and the Galactic Center
• Discovery of a fourth arc in Abell 2626 at 610 MHz with the GMRT: Spectral properties and possibilities for the origin
• Non-thermal filaments and AGN recurrent activity in the galaxy group Nest200047: a LOFAR, uGMRT, MeerKAT, VLA radio spectral analysis
• Cosmic dance in the Shapley Concentration Core II. The uGMRT-MeerKAT view of filaments in the brightest cluster galaxies and tailed radio galaxies in the A3528 cluster complex
• New filamentary remnant radio emission and duty cycle constraints in the radio galaxy NGC 6086
• Ageing and dynamics of the tailed radio galaxies in Abell 2142
• Revealing the intricacies of radio galaxies and filaments in the merging galaxy cluster Abell 2255. I. Insights from deep LOFAR-VLBI sub-arcsecond resolution images
• The structure of the giant radio fossil in the Ophiuchus galaxy cluster
• Fast and "lossless" propagation of relativistic electrons along magnetized non-thermal filaments in galaxy clusters and the Galactic Center region

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