LOFAR Discovery of a Radio Halo in the High-redshift Galaxy Cluster PSZ2 G099.86+58.45

Cassano, R.; Botteon, A.; Gennaro, G. Di; Brunetti, G.; Sereno, Mauro; Shimwell, T. W.; Weeren, R. J. van; Brüggen, M.; Gastaldello, F.; Izzo, L.; Bîrzan, L.; Bonafede, A.; Cuciti, V.; Gasperin, F. de; Röttgering, H. J. A.; Hardcastle, M. J.; Mechev, A. P.; Tasse, C.

doi:10.3847/2041-8213/ab32ed

Cited by 18 publications

(26 citation statements)

References 53 publications

(49 reference statements)

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“…In these observations, hints of a halo are present only at the 2σ rms level (with σ rms,VLA = 20 µJy beam −1 ). We repeated the flux measurement, covering the same region as the LOFAR halo and finding a flux of S 1500 ∼ 1.0 ± 0.4 mJy, in agreement with the flux density reported in Cassano et al (2019). This VLA flux density suggests a steepening towards GHz frequencies, with α 650 1500 ∼ −1.7 ± 0.5.…”

Section: Psz2 G09986+5845supporting

confidence: 86%

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A LOFAR-uGMRT spectral index study of distant radio halos

Di Gennaro,

van Weeren,

Cassano

et al. 2021

Preprint

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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 largescale turbulence. Aims. Current re-acceleration models predict that a significant number of halos at high redshift should be characterised by very steep spectra (α < −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 nondetections, 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.

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Section: Psz2 G09986+5845supporting

confidence: 86%

“…As for PSZ2 G091.83+26.11, we also detect ultra-steep spectra from source A (α 144 600 ∼ −1.7) and source C (α 144 650 ∼ −2.5) in this cluster, as was also mentioned by Cassano et al (2019).…”

Section: Psz2 G09986+5845supporting

confidence: 85%

A LOFAR-uGMRT spectral index study of distant radio halos

Di Gennaro,

van Weeren,

Cassano

et al. 2021

Preprint

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“…The observed decline is less prominent at low frequencies due to the increasing population of very steep spectrum halos that are expected to be more common at high redshift. Depending on the clusters magnetic field strength, a fraction of halos up to 10-25% in clusters with M 500 ∼ (3 − 4) × 10 14 M at a redshift of 0.7 is predicted to be observed with LOFAR (Cassano et al 2019). Better X-ray data with modern telescopes are needed to obtain a good estimate of the cluster mass and dynamical state.…”

Section: Discussionmentioning

confidence: 99%

“…We believe that the emission that is being picked up in the core is most likely AGN related, also because radio halos are expected to be intrinsically less luminous (by a factor of B 2 /B 2 CMB ) with higher redshift due to inverse Compton losses (e.g., Enßlin & Röttgering 2002;Cassano et al 2006Cassano et al , 2019. Even assuming a magnetic field of a few µG for the cluster at z = 1.71 (e.g., Domínguez-Fernández et al 2019), the synchrotron radiation would be reduced by about two orders of magnitude, making the detection of such a halo extremely unlikely by simple energetic arguments.…”

Section: Sparcs1049+56mentioning

confidence: 99%

Diffuse radio emission from galaxy clusters in the LOFAR Two-metre Sky Survey Deep Fields

Osinga

Weeren

Boxelaar

et al. 2021

A&A

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Low-frequency radio observations are revealing an increasing number of diffuse synchrotron sources from galaxy clusters, primarily in the form of radio halos or radio relics. The existence of this diffuse synchrotron emission indicates the presence of relativistic particles and magnetic fields. It is still an open question as to exactly what mechanisms are responsible for the population of relativistic electrons driving this synchrotron emission. The LOFAR Two-metre Sky Survey Deep Fields offer a unique view of this problem. Reaching noise levels below 30 μJy beam−1, these are the deepest images made at the low frequency of 144 MHz. This paper presents a search for diffuse emission in galaxy clusters in the first data release of the LOFAR Deep Fields. We detect a new high-redshift radio halo with a flux density of 8.9 ± 1.0 mJy and corresponding luminosity of P144MHz = (3.6 ± 0.6) × 1025 W Hz−1 in an X-ray detected cluster at z = 0.77 with a mass estimate of M500 = 3.3−1.7+1.1 × 1014 M⊙. Deep upper limits are placed on clusters with non-detections. We compare the results to the correlation between halo luminosity and cluster mass derived for radio halos found in the literature. This study is one of a few to find diffuse emission in low mass (M500 < 5 × 1014 M⊙) systems and shows that deep low-frequency observations of galaxy clusters are fundamental for opening up a new part of parameter space in the study of non-thermal phenomena in galaxy clusters.

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“…This extraction and re-calibration scheme has been already applied in recent LOFAR works (e.g. Hardcastle et al 2019;Cassano et al 2019;Botteon et al 2019), and it will be discussed in more detail in a forthcoming paper (van Weeren et al, in prep. ).…”

Section: Introductionmentioning

confidence: 99%

The Beautiful Mess in Abell 2255

Botteon

Brunetti

Weeren

et al. 2020

ApJ

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We present LOFAR observations of one of the most spectacular objects in the radio sky: Abell 2255. This is a nearby (z = 0.0806) merging galaxy cluster hosting one of the first radio halos ever detected in the intra-cluster medium (ICM). The deep LOFAR images at 144 MHz of the central ∼ 10 Mpc 2 region show a plethora of emission on different scales, from tens of kpc to above Mpc sizes. In this work, we focus on the innermost region of the cluster. Among the numerous interesting features observed, we discover remarkable bright and filamentary structures embedded in the radio halo. We incorporate archival WSRT 1.2 GHz data to study the spectral properties of the diffuse synchrotron emission and find a very complex spectral index distribution in the halo spanning a wide range of values. We combine the radio data with Chandra observations to investigate the connection between the thermal and non-thermal components by quantitatively comparing the radio and X-ray surface brightness and the spectral index of the radio emission with the thermodynamical quantities of the ICM. Despite the multitude of structures observed in the radio halo, we find that the X-ray and radio emission are overall well correlated. The fact that the steepest spectrum emission is located in the cluster center and traces regions with high entropy possibly suggests the presence of seed particles injected by radio galaxies that are spread in the ICM by turbulence generating the extended radio halo.

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LOFAR Discovery of a Radio Halo in the High-redshift Galaxy Cluster PSZ2 G099.86+58.45

Cited by 18 publications

References 53 publications

A LOFAR-uGMRT spectral index study of distant radio halos

A LOFAR-uGMRT spectral index study of distant radio halos

Diffuse radio emission from galaxy clusters in the LOFAR Two-metre Sky Survey Deep Fields

The Beautiful Mess in Abell 2255

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