HOW TO IDENTIFY AND SEPARATE BRIGHT GALAXY CLUSTERS FROM THE LOW-FREQUENCY RADIO SKY

Low frequency radio observations of galaxy clusters are a useful probe of the non-thermal intracluster medium (ICM), through observations of diffuse radio emission such as radio halos and relics. Current formation theories cannot fully account for some of the observed properties of this emission. In this study, we focus on the development of interferometric techniques for extracting extended, faint diffuse emissions in the presence of bright, compact sources in wide-field and broadband continuum imaging data. We aim to apply these techniques to the study of radio halos, relics and radio mini-halos using a uniformly selected and complete sample of galaxy clusters selected via the Sunyaev-Zel’dovich (SZ) effect by the Atacama Cosmology Telescope (ACT) project, and its polarimetric extension (ACTPol). We use the upgraded Giant Metrewave Radio Telescope (uGMRT) for targeted radio observations of a sample of 40 clusters. We present an overview of our sample, confirm the detection of a radio halo in ACT−CL J0034.4+0225, and compare the narrowband and wideband analysis results for this cluster. Due to the complexity of the ACT−CL J0034.4+0225 field, we use three pipelines to process the wideband data. We conclude that the experimental spam wideband pipeline produces the best results for this particular field. However, due to the severe artefacts in the field, further analysis is required to improve the image quality.

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Murchison Widefield Array detection of steep-spectrum, diffuse, non-thermal radio emission within Abell 1127

Publications of the Astronomical Society of Australia ◽

10.1017/pasa.2020.29 ◽

2020 ◽

Vol 37 ◽

Author(s):

S. W. Duchesne ◽

M. Johnston-Hollitt ◽

Z. Zhu ◽

R. B. Wayth ◽

J. L. B. Line

Keyword(s):

Radio Emission ◽

Galaxy Clusters ◽

Phase Ii ◽

Thermal Emission ◽

Low Frequency ◽

Radio Spectrum ◽

Discrete Source ◽

Thermal Radio ◽

Thermal Radio Emission ◽

Murchison Widefield Array

Abstract Diffuse, non-thermal emission in galaxy clusters is increasingly being detected in low-frequency radio surveys and images. We present a new diffuse, steep-spectrum, non-thermal radio source within the cluster Abell 1127 found in survey data from the Murchison Widefield Array (MWA). We perform follow-up observations with the ‘extended’ configuration MWA Phase II with improved resolution to better resolve the source and measure its low-frequency spectral properties. We use archival Very Large Array S-band data to remove the discrete source contribution from the MWA data, and from a power law model fit we find a spectral index of –1.83±0.29 broadly consistent with relic-type sources. The source is revealed by the Giant Metrewave Radio Telescope at 150 MHz to have an elongated morphology, with a projected linear size of 850 kpc as measured in the MWA data. Using Chandra observations, we derive morphological estimators and confirm quantitatively that the cluster is in a disturbed dynamical state, consistent with the majority of phoenices and relics being hosted by merging clusters. We discuss the implications of relying on morphology and low-resolution imaging alone for the classification of such sources and highlight the usefulness of the MHz to GHz radio spectrum in classifying these types of emission. Finally, we discuss the benefits and limitations of using the MWA Phase II in conjunction with other instruments for detailed studies of diffuse, steep-spectrum, non-thermal radio emission within galaxy clusters.

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Low frequency observations of radio relics and halos

Proceedings of the International Astronomical Union ◽

10.1017/s1743921318003861 ◽

2018 ◽

Vol 14 (S342) ◽

pp. 37-43

Author(s):

Ruta Kale

Keyword(s):

Galaxy Clusters ◽

Low Frequency ◽

Relativistic Electrons ◽

Physical Processes ◽

Low Frequencies ◽

Origin And Evolution ◽

Extended Sources ◽

Low Mass ◽

Statistical Studies

AbstractDiffuse radio emission from galaxy clusters in the form of radio halos and relics are tracers of the shocks and turbulence in the intra-cluster medium. The imprints of the physical processes that govern their origin and evolution can be found in their radio morphologies and spectra. The role of mildly relativistic population of electrons may be crucial for the acceleration mechanisms to work efficiently. Low frequency observations with telescopes that allow imaging of extended sources over a broad range of low frequencies (<2 GHz) offer the best tools to study these sources. I will review the Giant Metrewave Radio Telescope (GMRT) observations in the past few years that have led to: i) statistical studies of large samples of galaxy clusters, ii) opening of the discovery space in low mass clusters and iii) tracing the spectra of seed relativistic electrons using the Upgraded GMRT.

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Warm-hot gas in X-ray bright galaxy clusters and the H i-deficient circumgalactic medium in dense environments

Monthly Notices of the Royal Astronomical Society ◽

10.1093/mnras/stx3170 ◽

2017 ◽

Vol 475 (2) ◽

pp. 2067-2085 ◽

Cited By ~ 17

Author(s):

Joseph N Burchett ◽

Todd M Tripp ◽

Q Daniel Wang ◽

Christopher N A Willmer ◽

David V Bowen ◽

...

Keyword(s):

Galaxy Clusters ◽

Bright Galaxy ◽

X Ray ◽

Hot Gas ◽

Circumgalactic Medium

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Low Frequency Radio Observations of Galaxy Clusters and Groups

10.1007/978-3-319-97976-2 ◽

2018 ◽

Author(s):

Thérèse Cantwell

Keyword(s):

Galaxy Clusters ◽

Low Frequency ◽

Radio Observations

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Diffuse Extragalactic Emission at Low Frequencies within the Epoch of Reionization 0-hour Field

10.26686/wgtn.17060021.v1 ◽

2021 ◽

Author(s):

◽

Stefan Duchesne

Keyword(s):

Radio Emission ◽

Sample Size ◽

Galaxy Clusters ◽

Low Frequency ◽

Small Sample ◽

Point Sources ◽

Scaling Relations ◽

Low Frequencies ◽

Cluster Emission ◽

Radio Halo

<p>Low-frequency radio imaging of the southern sky has become available with the advent of the Murchison Widefield Array (MWA). The topic of this thesis is the study of extended, low-frequency radio emission, with a primary focus on the non-thermal synchrotron emission associated with the intra-cluster medium (ICM) of galaxy clusters. We do not limit the study to such emission, however, and investigate a small sample of other interesting and extended radio emission from objects in the southern sky. A significant portion of this work is invested in detecting, and characterising, extended, diffuse radio emission from galaxy clusters within a 45 degree by 45 degree region of the southern sky centred on R.A. = 0 hours, decl. = -27 degrees. This field is chosen as a deep MWA image has been made available which is sensitive to extended structures. Within the field we search for low-frequency, diffuse cluster emission, previously detected or otherwise. In doing so we find 34 diffuse radio sources, 3 of which are newly detected haloes, 1 newly detected relic with many new candidates of each. Further, we detect a new phoenix candidate as well as 2 candidate dead radio galaxies at the centre of clusters. We confirm previous observations of such emission as well, and measure properties such as their integrated flux densities, spectral indices, and sizes where possible. We compare our sample of haloes with previously detected haloes and revisit established scaling relations of the radio halo power with the cluster X-ray luminosity and mass. We find that both scaling relations are consistent with previous findings despite the increase in sample size, though note that the raw scatter in the data for best-fitting parameters increases with increase in sample size. In this, we demonstrate the utility of low-frequency radio telescopes like the MWA in detecting such emission, showing that the MWA is pushing into higher-redshift, lower-mass systems, though we caution that the low resolution of the MWA can work against us. We follow-up on two galaxy clusters found to host extended emission - Abell S1136 and Abell S1063. In the case of Abell S1136 we observe the emission at its centre with the Australia Telescope Compact Array (ATCA) and determine the presence of a core, suggesting the emission to be that of an ancient episode of an active galactic nucleus in the central elliptical of the cluster, ESO 470-G020. After reducing archival ATCA data for Abell S1063 we find no evidence of a halo and consider the source to be constructed of blended point sources. We close with a description of a strong double-lobed radio source associated with a non-elliptical host ESO 472-G013, likely a spiral or irregular galaxy, that was found serendipitously whilst searching for diffuse cluster emission. We explore the host within the context of star-formation, and consider the possible origins of the AGN and lobes due to interaction with either the nearby spiral, ESO 472-G012, or a past or ongoing merger event.</p>

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Particle re-acceleration in the ICM and low-frequency observations

Proceedings of the International Astronomical Union ◽

10.1017/s1743921307011052 ◽

2006 ◽

Vol 2 (14) ◽

pp. 374-375

Author(s):

Gianfranco Brunetti

Keyword(s):

Radio Emission ◽

Galaxy Clusters ◽

Low Frequency ◽

Radio Observations ◽

Low Frequencies

AbstractThe particle reaceleration model is one of the most promising possibilities to explain the Mpc-scale diffuse radio emission detected in a number of galaxy clusters. Ongoing and future radio observations at low frequencies may help in constraining and testing this model.

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Revived fossil plasma sources in galaxy clusters

Astronomy and Astrophysics ◽

10.1051/0004-6361/201936560 ◽

2020 ◽

Vol 634 ◽

pp. A4 ◽

Cited By ~ 4

Author(s):

S. Mandal ◽

H. T. Intema ◽

R. J. van Weeren ◽

T. W. Shimwell ◽

A. Botteon ◽

...

Keyword(s):

Particle Acceleration ◽

Galaxy Clusters ◽

Radiative Lifetime ◽

Low Frequency ◽

Radio Spectrum ◽

Optical Observations ◽

Relativistic Electrons ◽

Plasma Sources ◽

X Ray ◽

Sky Survey

It is well established that particle acceleration by shocks and turbulence in the intra-cluster medium can produce cluster-scale synchrotron emitting sources. However, the detailed physics of these particle acceleration processes is still not well understood. One of the main open questions is the role of fossil relativistic electrons that have been deposited in the intracluster medium (ICM) by radio galaxies. These synchrotron-emitting electrons are very difficult to study as their radiative lifetime is only tens of Myr at gigahertz frequencies, and they are therefore a relatively unexplored population. Despite the typical steep radio spectrum due to synchrotron losses, these fossil electrons are barely visible even at radio frequencies well below the gigahertz level. However, when a pocket of fossil radio plasma is compressed, it boosts the visibility at sub-gigahertz frequencies, creating what are known as radio phoenices. This compression can be the result of bulk motion and shocks in the ICM due to merger activity. In this paper we demonstrate the discovery potential of low-frequency radio sky surveys to find and study revived fossil plasma sources in galaxy clusters. We used the 150 MHz TIFR GMRT Sky Survey and the 1.4 GHz NVSS sky survey to identify candidate radio phoenices. A subset of three candidates was studied in detail using deep multi-band radio observations (LOFAR and GMRT), X-ray obserations (Chandra or XMM-Newton), and archival optical observations. Two of the three sources are new discoveries. Using these observations, we identified common observational properties (radio morphology, ultra-steep spectrum, X-ray luminosity, dynamical state) that will enable us to identify this class of sources more easily, and will help us to understand the physical origin of these sources.

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Low-frequency integrated radio spectra of diffuse, steep-spectrum sources in galaxy clusters: palaeontology with the MWA and ASKAP

Publications of the Astronomical Society of Australia ◽

10.1017/pasa.2021.45 ◽

2021 ◽

Vol 38 ◽

Author(s):

S. W. Duchesne ◽

M. Johnston-Hollitt ◽

I. Bartalucci

Keyword(s):

Galaxy Clusters ◽

Thermal Emission ◽

Low Frequency ◽

Present Sample ◽

Mass Scaling ◽

Frequency Coverage ◽

Murchison Widefield Array ◽

Radio Power ◽

Selection Of

Abstract Galaxy clusters have been found to host a range of diffuse, non-thermal emission components, generally with steep, power law spectra. In this work we report on the detection and follow-up of radio halos, relics, remnant radio galaxies, and other fossil radio plasmas in Southern Sky galaxy clusters using the Murchison Widefield Array and the Australian Square Kilometre Array Pathfinder. We make use of the frequency coverage between the two radio interferometers—from 88 to $\sim\!900$ MHz—to characterise the integrated spectra of these sources within this frequency range. Highlights from the sample include the detection of a double relic system in Abell 3186, a mini-halo in RXC J0137.2–0912, a candidate halo and relic in Abell 3399, and a complex multi-episodic head-tail radio galaxy in Abell 3164. We compare this selection of sources and candidates to the literature sample, finding sources consistent with established radio power–cluster mass scaling relations. Finally, we use the low-frequency integrated spectral index, $\alpha$ ( $S_v \propto v^\alpha$ ), of the detected sample of cluster remnants and fossil sources to compare with samples of known halos, relics, remnants and fossils to investigate a possible link between their electron populations. We find the distributions of $\alpha$ to be consistent with relic and halo emission generated by seed electrons that originated in fossil or remnant sources. However, the present sample sizes are insufficient to rule out other scenarios.

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