Origin of the ring structures in Hercules A -- Sub-arcsecond 144 MHz to 7 GHz observations

Abstract

The prominent radio source Hercules A features complex structures in its radio lobes. Although it is one of the most comprehensively studied sources in the radio sky, the origin of the ring structures in the Hercules A radio lobes remains an open question. We present the first sub-arcsecond angular resolution images at low frequencies (<300 MHz) of Hercules A, made with the International LOFAR Telescope. With the addition of data from the Karl G. Jansky Very Large Array, we mapped the structure of the lobes from 144 MHz to 7 GHz. We explore the origin of the rings within the lobes of Hercules A, and test whether their properties are best described by a shock model, where shock waves are produced by the jet propagating in the radio lobe, or by an inner-lobe model, where the rings are formed by decelerated jetted plasma. From spectral index mapping our large frequency coverage reveals that the curvature of the different ring spectra increases with distance away from the central active galactic nucleus. We demonstrate that the spectral shape of the rings is consistent with synchrotron aging, which speaks in favor of an inner-lobe model where the rings are formed from the deposition of material from past periods of intermittent core activity.

arXiv commentAccepted for a special issue of A&A on sub-arcsecond imaging with LOFAR

References in corpus (30)

• LOFAR: The LOw-Frequency ARray
• WSClean: an implementation of a fast, generic wide-field imager for radio astronomy
• A very deep Chandra observation of the Perseus cluster: shocks, ripples and conduction
• Radiative Efficiency and Content of Extragalactic Radio Sources: Toward a Universal Scaling Relation Between Jet Power and Radio Power
• An Accurate Flux Density Scale from 50 MHz to 50 GHz
• A broadband flux scale for low frequency radio telescopes
• LOFAR facet calibration
• Reviving Fossil Radio Plasma in Clusters of Galaxies by Adiabatic Compression in Environmental Shock Waves
• LOFAR 150-MHz observations of the Boötes field: Catalogue and Source Counts
• X-ray Emission Properties of Large Scale Jets, Hotspots and Lobes in Active Galactic Nuclei
• Systematic effects in LOFAR data: A unified calibration strategy
• Cosmic ray feedback in hydrodynamical simulations of galaxy formation
• X-ray Supercavities in the Hydra A Cluster and the Outburst History of the Central Galaxy's Active Nucleus
• Extragalactic Peaked-Spectrum Radio Sources at Low Frequencies
• Spectral ageing in the lobes of FR-II radio galaxies: New methods of analysis for broadband radio data
• AGN Jet Kinetic Power and the Energy Budget of Radio Galaxy Lobes
• Spectral ageing in the lobes of cluster-centre FR-II radio galaxies
• Cycling of the powerful AGN in MS 0735.6+7421 and the duty cycle of radio AGN in Clusters
• Sub-arcsecond imaging with the International LOFAR Telescope I. Foundational calibration strategy and pipeline
• A multiband study of Hercules A. II. Multifrequency VLA imaging
• LBCS: the LOFAR Long-Baseline Calibrator Survey
• Shock heating by FR I radio sources in galaxy clusters
• Sub-arcsecond imaging with the International LOFAR Telescope: II. Completion of the LOFAR Long-Baseline Calibrator Survey
• Production of ring-like structure in the cocoon of Hercules A
• AGN duty cycle estimates for the ultra-steep spectrum radio relic VLSS J1431.8+1331
• A multiband study of Hercules A. I. ROSAT observations of the intracluster medium
• First Results of the 74 MHz VLA-Pie Town Link. Hercules A at Low Frequencies
• Very Large Array observations of the mini-halo and AGN feedback in the Phoenix cluster
• Probing the pc- and kpc-scale environment of the powerful radio galaxy Hercules A
• Hubble Space Telescope Observations of Dusty Filaments in Hercules A: Evidence for Entrainment

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• The Dynamics and Energetics of Remnant and Restarting RLAGN
• A low frequency sub-arcsecond view of powerful radio galaxies in rich-cluster environments: 3C 34 and 3C 320
• Search and analysis of giant radio galaxies with associated nuclei (SAGAN) V. Study of giant double-double radio galaxies from LoTSS DR2
• On the large scale morphology of Hercules A: destabilized hot jets?
• 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
• Cocoon shock, X-ray cavities and extended Inverse Compton emission in Hercules A: clues from Chandra observations
• A novel radio imaging method for physical spectral index modelling
• The structure of the giant radio fossil in the Ophiuchus galaxy cluster
• The LOFAR sub-arcsecond view of the high-redshift radio relic in PSZ2G091.83+26.11
• Revealing the intricacies of radio galaxies and filaments in the merging galaxy cluster Abell 2255. II. Properties of filaments using multi-frequency radio data