Relics as Probes of Galaxy Cluster Mergers

Weeren, R. J. van; Brüggen, M.; Röttgering, H. J. A.; Hoeft, M.

doi:10.1007/s12036-011-9108-2

Cited by 97 publications

(164 citation statements)

References 20 publications

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“…The shock velocities are also estimated as v shock:n ∼ 2300 km s −1 and v shock:s ∼ 2000 km s −1 , respectively. This suggests that the merger happened ∼0.6 Gyr ago, in agreement with estimates based on hydrodynamical simulation and dynamical analysis (van Weeren et al 2011;Stroe et al 2014a;Dawson et al, in prep.). The observed radio spectral index of the northern relic (Stroe et al 2014a) is consistent with what would be expected from diffusive shock acceleration in a shock with the observed Mach number and compression.…”

Section: Discussionsupporting

confidence: 88%

SuzakuX-ray study of the double radio relic galaxy cluster CIZA J2242.8+5301

Akamatsu

Weeren

Ogrean

et al. 2015

A&A

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105

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Context. We present the results from Suzaku observations of the merging cluster of galaxies CIZA J2242.8+5301 at z = 0.192. Aims. To study the physics of gas heating and particle acceleration in cluster mergers, we investigated the X-ray emission from CIZA J2242.8+5301, which hosts two giant radio relics in the northern and southern part of the cluster. Methods. We analyzed data from three-pointed Suzaku observations of CIZA J2242.8+5301 to derive the temperature distribution in four different directions. Results. The intracluster medium (ICM) temperature shows a remarkable drop from 8.5 +0.8 −0.6 keV to 2.7 +0.7 −0.4 keV across the northern radio relic. The temperature drop is consistent with a Mach number M n = 2.7 +0.7 −0.4 and a shock velocity v shock:n = 2300 +700 −400 km s −1 . We also confirm the temperature drop across the southern radio relic. However, the ICM temperature beyond this relic is much higher than beyond the northern relic, which gives a Mach number M s = 1.7 +0.4 −0.3 and shock velocity v shock:s = 2040 +550 −410 km s −1 . These results agree with other systems showing a relationship between the radio relics and shock fronts which are induced by merging activity. We compare the X-ray derived Mach numbers with the radio derived Mach numbers from the radio spectral index under the assumption of diffusive shock acceleration in the linear test particle regime. For the northern radio relic, the Mach numbers derived from X-ray and radio observations agree with each other. Based on the shock velocities, we estimate that CIZA J2242.8+5301 is observed approximately 0.6 Gyr after core passage. The magnetic field pressure at the northern relic is estimated to be 9% of the thermal pressure.

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Section: Discussionsupporting

confidence: 88%

SuzakuX-ray study of the double radio relic galaxy cluster CIZA J2242.8+5301

Akamatsu

Weeren

Ogrean

et al. 2015

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105

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“…Usually shock surfaces are curved and not very linear over distances of more than a Mpc (e.g., Hoeft et al 2008;Battaglia et al 2009;Vazza et al 2009;Skillman et al 2011). The ongoing merger event for 1RXS J0603.3+4214 is probably more complex than the "simple" binary merger events that are thought to give rise to symmetric double radio relics (e.g., Roettiger et al 1999;van Weeren et al 2011a). Deep X-ray observations will be needed to investigate whether the relic is indeed associated with such a linear shock front.…”

Section: Discussionmentioning

confidence: 99%

The “toothbrush-relic”: evidence for a coherent linear 2-Mpc scale shock wave in a massive merging galaxy cluster?

Weeren

Röttgering

Intema

et al. 2012

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Some merging galaxy clusters host diffuse extended radio emission, so-called radio halos and relics, unrelated to individual galaxies. The origin of these halos and relics is still debated, although there is compelling evidence now that they are related to cluster merger events. Here we present detailed Westerbork Synthesis Radio Telescope (WSRT) and Giant Metrewave Radio Telescope (GMRT) radio observations between 147 MHz and 4.9 GHz of a new radio-selected galaxy cluster 1RXS J0603.3+4214, for which we find a redshift of 0.225. The cluster is detected as an extended X-ray source in the ROSAT All Sky Survey with an X-ray luminosity of L X, 0.1−2.4 keV ∼ 1 × 10 45 erg s −1 . The cluster hosts a large bright 1.9 Mpc radio relic, an elongated ∼2 Mpc radio halo, and two fainter smaller radio relics. The large radio relic has a peculiar linear morphology. For this relic we observe a clear spectral index gradient from the front of the relic towards the back, in the direction towards the cluster center. Parts of this relic are highly polarized with a polarization fraction of up to 60%. We performed rotation measure (RM) synthesis between 1.2 and 1.7 GHz. The results suggest that for the west part of the large relic some of the Faraday rotation is caused by the intracluster medium and not only due to galactic foregrounds. We also carried out a detailed spectral analysis of this radio relic and created radio color-color diagrams. We find (i) an injection spectral index of −0.6 to −0.7; (ii) steepening spectral index and increasing spectral curvature in the post-shock region; and (iii) an overall power-law spectrum between 74 MHz and 4.9 GHz with α = −1.10 ± 0.02. Mixing of emission in the beam from regions with different spectral ages is probably the dominant factor that determines the shape of the radio spectra. Changes in the magnetic field, total electron content, or adiabatic gains/losses do not play a major role. A model in which particles are (re)accelerated in a first order Fermi process at the front of the relic provides the best match to the observed spectra. We speculate that in the postshock region particles are re-accelerated by merger induced turbulence to form the radio halo as the relic and halo are connected. The orientation of the bright relic and halo indicate a north-south merger event, but the peculiar linear shape and the presence of another relic, perpendicular to the bright relic, suggest a more complex merger event. Deep X-ray observations will be needed to determine the merger scenario.

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“…Hydrodynamical simulations, radio spectral modelling and an analytical dynamics analysis suggest that the 'Sausage' corepassage has happened ∼ 1.0 Gyr ago, at a relative speed of ∼ 2000 − 2500 km s −1 (Dawson et al submitted;van Weeren et al 2011;Stroe et al 2014c), making it a younger merger than the possibly ∼ 2 Gyr old 'Toothbrush' merger (Brüggen et al 2012). The emitters for the 'Sausage' field (left panel) and the 'Toothbrush' field (right panel) in red circles and sources selected as Hα emitters in the filled circles, overlaid on a Giant Meterwave Radio Telescope 323 MHz radio images in grey intensity.…”

Section: The 'Sausage' and 'Toothbrush' Clustersmentioning

confidence: 99%

“…In the case of the 'Sausage' cluster, a binary merger lead to the formation of two unequal relics along the merger axis (van Weeren et al 2011). The northern relic has a stronger Mach number than the southern one by a factor of ∼ 2 (Stroe et al 2013).…”

Section: Cause For Enhanced Star Formation In the 'Sausage' Clustermentioning

confidence: 99%

The rise and fall of star formation in z ∼ 0.2 merging galaxy clusters

Stroe¹,

Sobral²,

Dawson³

et al. 2015

Monthly Notices of the Royal Astronomical Society

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CIZA J2242.8+5301 ('Sausage') and 1RXS J0603.3+4213 ('Toothbrush') are two lowredshift (z ∼ 0.2), massive (∼ 2 × 10 15 M ), post-core passage merging clusters, which host shock waves traced by diffuse radio emission. To study their star-formation properties, we uniformly survey the 'Sausage' and 'Toothbrush' clusters in broad and narrow band filters and select a sample of 201 and 463 line emitters, down to a rest-frame equivalent width (13Å). We robustly separate between Hα and higher redshift emitters using a combination of optical multi-band (B, g, V, r, i, z) and spectroscopic data. We build Hα luminosity functions for the entire cluster region, near the shock fronts, and away from the shock fronts and find striking differences between the two clusters. In the dynamically younger, 1 Gyr old 'Sausage' cluster we find numerous (59) Hα emitters above a star-formation rate (SFR) of 0.17 M yr −1 surprisingly located in close proximity to the shock fronts, embedded in very hot intra-cluster medium plasma. The SFR density for the cluster population is at least at the level of typical galaxies at z ∼ 2. Down to the same star-formation rate, the possibly dynamically more evolved 'Toothbrush' cluster has only 9 Hα galaxies. The cluster Hα galaxies fall on the SFRstellar mass relation z ∼ 0.2 for the field. However, the 'Sausage' cluster has an Hα emitter density > 20 times that of blank fields. If the shock passes through gas-rich cluster galaxies, the compressed gas could collapse into dense clouds and excite star-formation for a few 100 Myr. This process ultimately leads to a rapid consumption of the molecular gas, accelerating the transformation of gas-rich field spirals into cluster S0s or ellipticals.

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Relics as Probes of Galaxy Cluster Mergers

Cited by 97 publications

References 20 publications

SuzakuX-ray study of the double radio relic galaxy cluster CIZA J2242.8+5301

SuzakuX-ray study of the double radio relic galaxy cluster CIZA J2242.8+5301

The “toothbrush-relic”: evidence for a coherent linear 2-Mpc scale shock wave in a massive merging galaxy cluster?

The rise and fall of star formation in z ∼ 0.2 merging galaxy clusters

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