X-ray and Radio Observations of the Radio Relic Galaxy Clusters 1RXS J0603.3+4214 and RXC J1053.7+5453

We study two galaxy clusters with radio relics, 1RXS J0603.3+4214 and RXC J1053.7+5453, through X-ray and radio observations. Radio relics are diffuse non-thermal radio sources found in outskirts of galaxy clusters. Because of their shape and location, they are thought to be related to cluster merger shocks. The galaxy cluster 1RXS J0603.3+4214 has a well-known linear-shape “toothbrush” radio relic. We investigate the temperature structure across the relic to constrain the Mach number of the associated shock. The results are compared with radio spectral results, which suggest that a simple diffusive shock acceleration model does not hold for this relic. The RXC J1053.7+5453 harbors a standard arc-like relic. We also get the Mach number from the temperature profile. In addition, we found an edge-like structure in the X-ray image between the X-ray peak and relic. We investigate the density and temperature profiles across the edge and found that the structure is likely relevant to not a shock but a contact discontinuity.

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Radio observations of the merging galaxy cluster Abell 520

Astronomy and Astrophysics ◽

10.1051/0004-6361/201833900 ◽

2019 ◽

Vol 622 ◽

pp. A20 ◽

Cited By ~ 10

Author(s):

D. N. Hoang ◽

T. W. Shimwell ◽

R. J. van Weeren ◽

G. Brunetti ◽

H. J. A. Röttgering ◽

...

Keyword(s):

Mach Number ◽

Radio Emission ◽

Low Frequency ◽

Galaxy Cluster ◽

Shock Acceleration ◽

Relativistic Electrons ◽

Diffusive Shock Acceleration ◽

Cluster Emission ◽

X Ray ◽

Extended Radio

Context. Extended synchrotron radio sources are often observed in merging galaxy clusters. Studies of the extended emission help us to understand the mechanisms in which the radio emitting particles gain their relativistic energies. Aims. We examine the possible acceleration mechanisms of the relativistic particles that are responsible for the extended radio emission in the merging galaxy cluster Abell 520. Methods. We performed new 145 MHz observations with the LOw Frequency ARay (LOFAR) and combined these with archival Giant Metrewave Radio Telescope (GMRT) 323 MHz and Very Large Array (VLA) 1.5 GHz data to study the morphological and spectral properties of extended cluster emission. The observational properties are discussed in the framework of particle acceleration models associated with cluster merger turbulence and shocks. Results. In Abell 520, we confirm the presence of extended (760 × 950 kpc2) synchrotron radio emission that has been classified as a radio halo. The comparison between the radio and X-ray brightness suggests that the halo might originate in a cocoon rather than from the central X-ray bright regions of the cluster. The halo spectrum is roughly uniform on the scale of 66 kpc. There is a hint of spectral steepening from the SW edge towards the cluster centre. Assuming diffusive shock acceleration (DSA), the radio data are suggestive of a shock Mach number of ℳSW = 2.6−0.2+0.3 that is consistent with the X-ray derived estimates. This is in agreement with the scenario in which relativistic electrons in the SW radio edge gain their energies at the shock front via acceleration of either thermal or fossil electrons. We do not detect extended radio emission ahead of the SW shock that is predicted if the emission is the result of adiabatic compression. An X-ray surface brightness discontinuity is detected towards the NE region that may be a counter shock of Mach number ℳNEX = 1.52±0.05. This is lower than the value predicted from the radio emission which, assuming DSA, is consistent with ℳNE = 2.1 ± 0.2. Conclusions. Our observations indicate that the radio emission in the SW of Abell 520 is likely effected by the prominent X-ray detected shock in which radio emitting particles are (re-)accelerated through the Fermi-I mechanism. The NE X-ray discontinuity that is approximately collocated with an edge in the radio emission hints at the presence of a counter shock.

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Manufacturing cosmic rays in the evolving dynamical states of galaxy clusters

Monthly Notices of the Royal Astronomical Society ◽

10.1093/mnras/stz1785 ◽

2019 ◽

Vol 488 (1) ◽

pp. 1301-1319 ◽

Cited By ~ 1

Author(s):

Reju Sam John ◽

Surajit Paul ◽

Luigi Iapichino ◽

Karl Mannheim ◽

Harish Kumar

Keyword(s):

Cosmic Rays ◽

Galaxy Clusters ◽

Theoretical Calculations ◽

Shock Acceleration ◽

Diffusive Shock Acceleration ◽

X Ray ◽

Mass Scaling ◽

Dynamical Phase ◽

The Galaxy ◽

High Mach

ABSTRACT Galaxy clusters are known to be reservoirs of cosmic rays (CRs), as inferred from theoretical calculations or detection of CR-derived observables. CR acceleration in clusters is mostly attributed to the dynamical activity that produces shocks. Shocks in clusters emerge out of merger or accretion, but which one is more effective in producing CRs? at which dynamical phase? and why? To this aim, we study the production or injection of CRs through shocks and its evolution in the galaxy clusters using cosmological simulations with the enzo code. Particle acceleration model considered here is primarily the Diffusive Shock Acceleration (DSA) of thermal particles, but we also report a tentative study with pre-existing CRs. Defining appropriate dynamical states using the concept of virialization, we studied a sample of merging and non-merging clusters. We report that the merger shocks (with Mach number $\mathcal {M}\sim 2-5$) are the most effective CR producers, while high-Mach peripheral shocks (i.e. $\mathcal {M}\gt 5$) are mainly responsible for the brightest phase of CR injection in clusters. Clusters once merged, permanently deviate from CR and X-ray mass scaling of non-merging systems, enabling us to use it as a tool to determine the state of merger. Through a temporal and spatial evolution study, we found a strong correlation between cluster merger dynamics and CR injection. We observed that the brightest phase of X-ray and CR injection from clusters occurs, respectively, at about 1.0 and 1.5 Gyr after every mergers, and CR injection peaks near to the cluster virial radius (i.e r200). Delayed CR injection peaks found in this study deserve further investigation for possible impact on the evolution of CR-derived observables from galaxy clusters.

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Discovering the most elusive radio relic in the sky: diffuse shock acceleration caught in the act?

Monthly Notices of the Royal Astronomical Society Letters ◽

10.1093/mnrasl/slaa074 ◽

2020 ◽

Vol 496 (1) ◽

pp. L48-L53 ◽

Cited By ~ 2

Author(s):

Nicola T Locatelli ◽

Kamlesh Rajpurohit ◽

Franco Vazza ◽

Fabio Gastaldello ◽

Daniele Dallacasa ◽

...

Keyword(s):

Mach Number ◽

Surface Brightness ◽

Low Frequency ◽

Galaxy Cluster ◽

Total Power ◽

Shock Acceleration ◽

Diffusive Shock Acceleration ◽

The Galaxy ◽

Shock Mach Number ◽

New Generation

ABSTRACT The origin of radio relics is usually explained via diffusive shock acceleration (DSA) or re-acceleration of electrons at/from merger shocks in galaxy clusters. The case of acceleration is challenged by the low predicted efficiency of low Mach number merger shocks, unable to explain the power observed in most radio relics. In this letter, we present the discovery of a new giant radio relic around the galaxy cluster Abell 2249 ($z$ = 0.0838) using Low-Frequency Array (LOFAR). It is special since it has the lowest surface brightness of all known radio relics. We study its radio and X-ray properties combining LOFAR data with uGMRT, JVLA, and XMM. This object has a total power of $L_{1.4\rm\, GHz}=4.1\pm 0.8 \times 10^{23}$ W Hz−1 and integrated spectral index α = 1.15 ± 0.23. We infer for this radio relic a lower bound on the magnetization of $B\ge 0.4\, \mu$G, a shock Mach number of $\mathcal {M}\approx 3.79$, and a low acceleration efficiency consistent with DSA. This result suggests that a missing population of relics may become visible, thanks to the unprecedented sensitivity of the new generation of radio telescopes.

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Anisotropy of the galaxy cluster X-ray luminosity–temperature relation

Astronomy and Astrophysics ◽

10.1051/0004-6361/201731222 ◽

2018 ◽

Vol 611 ◽

pp. A50 ◽

Cited By ~ 5

Author(s):

Konstantinos Migkas ◽

Thomas H. Reiprich

Keyword(s):

Galaxy Clusters ◽

Statistical Significance ◽

Cosmological Parameters ◽

Galaxy Cluster ◽

Luminosity Distance ◽

Temperature Relation ◽

X Ray ◽

Two Samples ◽

The Galaxy ◽

Group A

We introduce a new test to study the cosmological principle with galaxy clusters. Galaxy clusters exhibit a tight correlation between the luminosity and temperature of the X-ray-emitting intracluster medium. While the luminosity measurement depends on cosmological parameters through the luminosity distance, the temperature determination is cosmology-independent. We exploit this property to test the isotropy of the luminosity distance over the full extragalactic sky, through the normalization a of the LX–T scaling relation and the cosmological parameters Ωm and H0. To this end, we use two almost independent galaxy cluster samples: the ASCA Cluster Catalog (ACC) and the XMM Cluster Survey (XCS-DR1). Interestingly enough, these two samples appear to have the same pattern for a with respect to the Galactic longitude. More specifically, we identify one sky region within l ~ (−15°, 90°) (Group A) that shares very different best-fit values for the normalization of the LX–T relation for both ACC and XCS-DR1 samples. We use the Bootstrap and Jackknife methods to assess the statistical significance of these results. We find the deviation of Group A, compared to the rest of the sky in terms of a, to be ~2.7σ for ACC and ~3.1σ for XCS-DR1. This tension is not significantly relieved after excluding possible outliers and is not attributed to different redshift (z), temperature (T), or distributions of observable uncertainties. Moreover, a redshift conversion to the cosmic microwave background (CMB) frame does not have an important impact on our results. Using also the HIFLUGCS sample, we show that a possible excess of cool-core clusters in this region, is not able to explain the obtained deviations. Furthermore, we tested for a dependence of the results on supercluster environment, where the fraction of disturbed clusters might be enhanced, possibly affecting the LX–T relation. We indeed find a trend in the XCS-DR1 sample for supercluster members to be underluminous compared to field clusters. However, the fraction of supercluster members is similar in the different sky regions, so this cannot explain the observed differences, either. Constraining Ωm and H0 via the redshift evolution of LX–T and the luminosity distance via the flux–luminosity conversion, we obtain approximately the same deviation amplitudes as for a. It is interesting that the general observed behavior of Ωm for the sky regions that coincide with the CMB dipole is similar to what was found with other cosmological probes such as supernovae Ia. The reason for this behavior remains to be identified.

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On the influence of supra-thermal particle acceleration on the morphology of low-Mach, high-β shocks

Monthly Notices of the Royal Astronomical Society ◽

10.1093/mnras/staa1771 ◽

2020 ◽

Vol 496 (3) ◽

pp. 3198-3208

Author(s):

Allard Jan van Marle

Keyword(s):

Mach Number ◽

Galaxy Cluster ◽

Cosmic Ray ◽

Shock Acceleration ◽

Diffusive Shock Acceleration ◽

Particle Injection ◽

Particle In Cell ◽

Injection Process ◽

The Magnetic Field ◽

High Computational Efficiency

ABSTRACT When two galaxy clusters encounter each other, the interaction results in a collisionless shock that is characterized by a low (1–4) sonic Mach number, and a high-Alfvénic Mach number. Our goal is to determine if, and to what extent, such shocks can accelerate particles to sufficient velocities that they can contribute to the cosmic ray spectrum. We combine two different computational methods, magnetohydrodynamics (MHD) and particle-in-cell (PIC) into a single code that allows us to take advantage of the high computational efficiency of MHD while maintaining the ability to model the behaviour of individual non-thermal particles. Using this method, we perform a series of simulations covering the expected parameter space of galaxy cluster collision shocks. Our results show that for shocks with a sonic Mach number below 2.25 no diffusive shock acceleration can take place because of a lack of instabilities in the magnetic field, whereas for shocks with a sonic Mach number $\ge \, 3$ the acceleration is efficient and can accelerate particles to relativistic speeds. In the regime between these two extremes, diffusive shock acceleration can occur but is relatively inefficient because of the time- and space-dependent nature of the instabilities. For those shocks that show efficient acceleration, the instabilities in the upstream gas increase to the point where they change the nature of the shock, which, in turn, will influence the particle injection process.

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SPIDERS: overview of the X-ray galaxy cluster follow-up and the final spectroscopic data release

Monthly Notices of the Royal Astronomical Society ◽

10.1093/mnras/staa2066 ◽

2020 ◽

Vol 497 (3) ◽

pp. 3976-3992 ◽

Cited By ~ 1

Author(s):

N Clerc ◽

C C Kirkpatrick ◽

A Finoguenov ◽

R Capasso ◽

J Comparat ◽

...

Keyword(s):

Galaxy Clusters ◽

Sample Selection ◽

Galaxy Cluster ◽

Sloan Digital Sky Survey ◽

Observable Universe ◽

Data Set ◽

X Ray ◽

Data Release ◽

The Galaxy

ABSTRACT SPIDERS (The SPectroscopic IDentification of eROSITA Sources) is a large spectroscopic programme for X-ray selected galaxy clusters as part of the Sloan Digital Sky Survey-IV (SDSS-IV). We describe the final data set in the context of SDSS Data Release 16 (DR16): the survey overall characteristics, final targeting strategies, achieved completeness, and spectral quality, with special emphasis on its use as a galaxy cluster sample for cosmology applications. SPIDERS now consists of about 27 000 new optical spectra of galaxies selected within 4000 photometric red sequences, each associated with an X-ray source. The excellent spectrograph efficiency and a robust analysis pipeline yield a spectroscopic redshift measurement success rate exceeding 98 per cent, with a median velocity accuracy of 20 km s−1 (at z = 0.2). Using the catalogue of 2740 X-ray galaxy clusters confirmed with DR16 spectroscopy, we reveal the 3D map of the galaxy cluster distribution in the observable Universe up to z ∼ 0.6. We highlight the homogeneity of the member galaxy spectra among distinct regions of the galaxy cluster phase space. Aided by accurate spectroscopic redshifts and by a model of the sample selection effects, we compute the galaxy cluster X-ray luminosity function and we present its lack of evolution up to z = 0.6. Finally we discuss the prospects of forthcoming large multiplexed spectroscopic programmes dedicated to follow up the next generation of all-sky X-ray source catalogues.

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Diffuse galaxy cluster emission at 168 MHz within the Murchison Widefield Array Epoch of Reionization 0-h field

Publications of the Astronomical Society of Australia ◽

10.1017/pasa.2021.7 ◽

2021 ◽

Vol 38 ◽

Author(s):

S. W. Duchesne ◽

M. Johnston-Hollitt ◽

A. R. Offringa ◽

G. W. Pratt ◽

Q. Zheng ◽

...

Keyword(s):

Galaxy Clusters ◽

Galaxy Cluster ◽

Scaling Relations ◽

Cluster Emission ◽

X Ray ◽

Diffuse Sources ◽

Radio Halo ◽

The Galaxy ◽

Murchison Widefield Array

Abstract We detect and characterise extended, diffuse radio emission from galaxy clusters at 168 MHz within the Epoch of Reionization 0-h field: a $45^{\circ} \times 45^{\circ}$ region of the southern sky centred on R. A. ${}= 0^{\circ}$ , decl. ${}=-27^{\circ}$ . We detect 29 sources of interest; a newly detected halo in Abell 0141; a newly detected relic in Abell 2751; 4 new halo candidates and a further 4 new relic candidates; and a new phoenix candidate in Abell 2556. Additionally, we find nine clusters with unclassifiable, diffuse steep-spectrum emission as well as a candidate double relic system associated with RXC J2351.0-1934. We present measured source properties such as their integrated flux densities, spectral indices ( $\alpha$ , where $S_\nu \propto \nu^\alpha$ ), and sizes where possible. We find several of the diffuse sources to have ultra-steep spectra including the halo in Abell 0141, if confirmed, showing $\alpha \leq -2.1 \pm 0.1$ with the present data making it one of the steepest-spectrum haloes known. Finally, we compare our sample of haloes with previously detected haloes and revisit established scaling relations of the radio halo power ( $P_{1.4}$ ) with the cluster X-ray luminosity ( $L_{\textrm{X}}$ ) and mass ( $M_{500}$ ). We find that the newly detected haloes and candidate haloes are consistent with the $P_{1.4}$ – $L_{\textrm{X}}$ and $P_{1.4}$ – $M_{500}$ relations and see an increase in scatter in the previously found relations with increasing sample size likely caused by inhomogeneous determination of $P_{1.4}$ across the full halo sample. We show that the MWA is capable of detecting haloes and relics within most of the galaxy clusters within the Planck catalogue of Sunyaev–Zel’dovich sources depending on exact halo or relic properties.

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Morphology of radio relics – I. What causes the substructure of synchrotron emission?

Monthly Notices of the Royal Astronomical Society ◽

10.1093/mnras/staa3018 ◽

2020 ◽

Vol 500 (1) ◽

pp. 795-816

Author(s):

P Domínguez-Fernández ◽

M Brüggen ◽

F Vazza ◽

W E Banda-Barragán ◽

K Rajpurohit ◽

...

Keyword(s):

Magnetic Field ◽

Mach Number ◽

Three Dimensional ◽

Cosmic Ray ◽

Shock Acceleration ◽

Synchrotron Emission ◽

Diffusive Shock Acceleration ◽

X Ray ◽

Set Up ◽

Index Maps

ABSTRACT High-resolution radio observations of cluster radio relics often show complex spatial and spectral features. However, it is not clear what these features reveal about the underlying magnetic field properties. We performed three-dimensional magnetohydrodynamical simulations of merger shock waves propagating through a magnetized, turbulent intracluster medium. Our model includes the diffusive shock acceleration (DSA) of cosmic ray electrons, their spatial advection and energy losses at run-time. With this set-up we can investigate the relation between radio substructure and pre-shock plasma conditions in the host cluster. We find that upstream turbulence plays a major role in shaping the properties of radio relics produced downstream. Within the assumption of DSA, we can reproduce the observed discrepancy between the X-ray derived Mach number of shocks, and the Mach number inferred from radio spectra. Our simulated spectral index maps and profiles across the radio relic also suggest that the standard deviation of the upstream magnetic field must be relatively small ($\sigma _B\le 1 \, \mu$G) in order to reproduce observations and therefore radio relics can potentially constrain the distribution of magnetic fields in galaxy clusters outskirts.

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