Subscribe to the gold package and get unlimited access to Shamra Academy
Register a new userRadio Relics Tracing the Projected Mass Distribution in CIZA J2242.8+5301
106
0
0.0
(
0
)
Ask ChatGPT about the research
No Arabic abstract
We present a weak-lensing analysis for the merging galaxy cluster, CIZA J2242.8+5301, hosting double radio relics, using three-band Subaru/Suprime-Cam imaging ($Brz$). Since the lifetime of dark matter halos colliding into clusters is longer than that of X-ray emitting gas halos, weak-lensing analysis is a powerful method to constrain a merger dynamics. Two-dimensional shear fitting using a clean background catalog suggests that the cluster undergoes a merger with a mass ratio of about 2:1. The main halo is located around the gas core in the southern region, while no concentrated gas core is associated with the northern sub halo. We find that the projected cluster mass distribution resulting from an unequal-mass merger is in excellent agreement with the curved shapes of the two radio relics and the overall X-ray morphology except for the lack of the northern gas core. The lack of a prominent radio halo enables us to constrain an upper limit of the fractional energy of magneto-hydrodynamics turbulence of $(delta B/B)^2<mathcal{O}(10^{-6})$ at a resonant wavenumber, by a balance between the acceleration time and the time after the core passage or the cooling time, with an assumption of resonant acceleration by second-order Fermi process.
rate research
Read More
Giant radio relics are the arc-shaped diffuse radio emission regions observed in the outskirts of some merging galaxy clusters. They are believed to trace shock-waves in the intra-cluster medium. Recent observations demonstrated that some prominent radio relics exhibit a steepening above 2 GHz in their radio spectrum. This challenges standard theoretical models because shock acceleration is expected to accelerate electrons to very high energies with a power-law distribution in momentum. In this work we attempt to reconcile these data with the shock-acceleration scenario. We propose that the spectral steepening may be caused by the highest energy electrons emitting preferentially in lower magnetic fields than the bulk of synchrotron bright electrons in relics. Here, we focus on a model with an increasing mag- netic field behind the shock front, which quickly saturates and then declines. We derive the time-evolution of cosmic-ray electron spectra in time variable magnetic fields and an expanding medium. We then apply the formalism on the large radio relic in the cluster CIZA J2242.8+5301 (the Sausage relic). We show that under favourable circumstances of magnetic field amplification downstream, our model can explain the observed radio spectrum, the brightness profile and the spectral index profile of the relic. A possible interpretation for the required amplification of the magnetic field downstream is a dynamo acting behind the shock with an injection scale of magnetic turbulence of about 10 kpc. Our models require injection efficiencies of CRe - which are in tension with simple diffusive shock acceleration from the thermal pool. We show that this problem can likely be alleviated considering pre-existing CRe.
We observed the galaxy cluster CIZA J2242.8+5301 with the Sardinia Radio Telescope to provide new constraints on its spectral properties at high frequency. We conducted observations in three frequency bands centred at 1.4 GHz, 6.6 GHz and 19 GHz, resulting in beam resolutions of 14$^{prime}$, 2.9$^{prime}$ and 1$^{prime}$ respectively. These single-dish data were also combined with archival interferometric observations at 1.4 and 1.7 GHz. From the combined images, we measured a flux density of ${rm S_{1.4GHz}=(158.3pm9.6),mJy}$ for the central radio halo and ${rm S_{1.4GHz}=(126pm8),mJy}$ and ${rm S_{1.4GHz}=(11.7pm0.7),mJy}$ for the northern and the southern relic respectively. After the spectral modelling of the discrete sources, we measured at 6.6 GHz ${rm S_{6.6GHz}=(17.1pm1.2),mJy}$ and ${rm S_{6.6GHz}=(0.6pm0.3),mJy}$ for the northern and southern relic respectively. Assuming simple diffusive shock acceleration, we interpret measurements of the northern relic with a continuous injection model represented by a broken power-law. This yields an injection spectral index ${rm alpha_{inj}=0.7pm0.1}$ and a Mach number ${rm M=3.3pm0.9}$, consistent with recent X-ray estimates. Unlike other studies of the same object, no significant steepening of the relic radio emission is seen in data up to 8.35 GHz. By fitting the southern relic spectrum with a simple power-law (${rm S_{ u}propto u^{-alpha}}$) we obtained a spectral index ${rm alphaapprox1.9}$ corresponding to a Mach number (${rm Mapprox1.8}$) in agreement with X-ray estimates. Finally, we evaluated the rotation measure of the northern relic at 6.6 GHz. These results provide new insights on the magnetic structure of the relic, but further observations are needed to clarify the nature of the observed Faraday rotation.
Multiwavelength studies of radio relics at merger shocks set powerful constraints on the relics origin and formation mechanism. However, for X-ray observations, a main difficulty is represented by the low X-ray surface brightness far out in the cluster outskirts, where relics are typically found. Here, we present XMM-Newton results from a 130-ks observation of CIZA J2242.8+5301, a cluster at z=0.19 that hosts a double radio relic. We focus on the well-defined northern relic. There is a difference of ~55% between the temperature we measure behind the relic, and the temperature measured with Suzaku. We analyse the reasons for this large discrepancy, and discuss the possibility of reliably measuring the temperature beyond the northern relic.
We studied the intracluster medium of the galaxy cluster CIZA J2242.8+5301 using deep XMM-Newton observations. The cluster hosts a remarkable 2-Mpc long, ~50-kpc wide radio relic that has been nicknamed the Sausage. A smaller, more irregular counter-relic is also present, along with a faint giant radio halo. We analysed the distribution of the ICM physical properties, and searched for shocks by trying to identify density and temperature discontinuities. East of the southern relic, we find evidence of shock compression corresponding to a Mach number of 1.3, and speculate that the shock extends beyond the length of the radio structure. The ICM temperature increases at the northern relic. More puzzling, we find a wall of hot gas east of the cluster centre. A partial elliptical ring of hot plasma appears to be present around the merger. While radio observations and numerical simulations predict a simple merger geometry, the X-ray results point towards a more complex merger scenario.
CIZA J2242.8+5301, a merging galaxy cluster at z=0.19, hosts a double-relic system and a faint radio halo. Radio observations at frequencies ranging from a few MHz to several GHz have shown that the radio spectral index at the outer edge of the N relic corresponds to a shock of Mach number 4.6+/-1.1, under the assumptions of diffusive shock acceleration of thermal particles in the test particle regime. Here, we present results from new Chandra observations of the cluster. The Chandra surface brightness profile across the N relic only hints to a surface brightness discontinuity (<2-sigma detection). Nevertheless, our reanalysis of archival Suzaku data indicates a temperature discontinuity across the relic that is consistent with a Mach number of 2.5+/-0.5, in agreement with previously published results. This confirms that the Mach number at the shock traced by the N relic is much weaker than predicted from the radio. Puzzlingly, in the Chandra data we also identify additional inner small density discontinuities both on and off the merger axis. Temperature measurements on both sides of the discontinuities do not allow us to undoubtedly determine their nature, although a shock front interpretation seems more likely. We speculate that if the inner density discontinuities are indeed shock fronts, then they are the consequence of violent relaxation of the dark matter cores of the clusters involved in the merger.
Log in to be able to interact and post comments
comments
Fetching comments
Sign in to be able to follow your search criteria
