On the Connection Between Giant Radio Halos and Cluster Mergers

Cassano, R.; Ettori, S.; Giacintucci, S.; Brunetti, G.; Markevitch, M.; Venturi, T.; Gitti, Myriam

doi:10.1088/2041-8205/721/2/l82

Cited by 320 publications

(564 citation statements)

References 29 publications

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“…The radio halo clusters are uniformly unrelaxed according to our X-ray morphological analysis (Section 5.4), while the clusters with only upper limits split between being relaxed and unrelaxed. These trends are consistent with previous work comparing the incidence of radio halos with other morphological estimators, namely power ratios, surface brightness concentration and/or centroid variance (Buote 2001, Cassano et al 2010. Similarly, all the clusters in our analysis which host radio relics (emission localized to cluster outskirts) according to the compilation of Feretti et al (2012) are found to be unrelaxed.…”

Section: Comparison With Radio Halo/relic Samplessupporting

confidence: 92%

Cosmology and astrophysics from relaxed galaxy clusters – I. Sample selection

Mantz

Allen

Morris

et al. 2015

Monthly Notices of the Royal Astronomical Society

109

191

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This is the first in a series of papers studying the astrophysics and cosmology of massive, dynamically relaxed galaxy clusters. Here we present a new, automated method for identifying relaxed clusters based on their morphologies in X-ray imaging data. While broadly similar to others in the literature, the morphological quantities that we measure are specifically designed to provide a fair basis for comparison across a range of data quality and cluster redshifts, to be robust against missing data due to point-source masks and gaps between detectors, and to avoid strong assumptions about the cosmological background and cluster masses. Based on three morphological indicators -Symmetry, Peakiness and Alignment -we develop the SPA criterion for relaxation. This analysis was applied to a large sample of cluster observations from the Chandra and ROSAT archives. Of the 361 clusters which received the SPA treatment, 57 (16 per cent) were subsequently found to be relaxed according to our criterion. We compare our measurements to similar estimators in the literature, as well as projected ellipticity and other image measures, and comment on trends in the relaxed cluster fraction with redshift, temperature, and survey selection method. Code implementing our morphological analysis will be made available on the web. 1

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Section: Comparison With Radio Halo/relic Samplessupporting

confidence: 92%

Cosmology and astrophysics from relaxed galaxy clusters – I. Sample selection

Mantz

Allen

Morris

et al. 2015

Monthly Notices of the Royal Astronomical Society

109

191

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“…High-mass clusters will be more recently formed through mergers and accretion which can in turn increase A phot and w (e.g. Cassano et al 2010;Nurgaliev et al 2017). From the optical perspective, we also find that high-mass clusters have velocity distributions which are less Gaussian than low-mass systems, in agreement with previous studies (Roberts & Parker 2017;de Carvalho et al 2017).…”

Section: The Anderson-darling Test As a Relaxation Proxysupporting

confidence: 91%

Connecting optical and X-ray tracers of galaxy cluster relaxation

Roberts

Parker

Hlavacek-Larrondo

2018

Monthly Notices of the Royal Astronomical Society

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Substantial effort has been devoted in determining the ideal proxy for quantifying the morphology of the hot intracluster medium in clusters of galaxies. These proxies, based on X-ray emission, typically require expensive, high-quality X-ray observations making them difficult to apply to large surveys of groups and clusters. Here, we compare optical relaxation proxies with X-ray asymmetries and centroid shifts for a sample of SDSS clusters with high-quality, archival X-ray data from Chandra and XMM-Newton. The three optical relaxation measures considered are: the shape of the member-galaxy projected velocity distribution -measured by the Anderson-Darling (AD) statistic, the stellar mass gap between the most-massive and second-most-massive cluster galaxy, and the offset between the most-massive galaxy (MMG) position and the luminosityweighted cluster centre. The AD statistic and stellar mass gap correlate significantly with X-ray relaxation proxies, with the AD statistic being the stronger correlator. Conversely, we find no evidence for a correlation between X-ray asymmetry or centroid shift and the MMG offset. High-mass clusters (M halo > 10 14.5 M ) in this sample have X-ray asymmetries, centroid shifts, and Anderson-Darling statistics which are systematically larger than for low-mass systems. Finally, considering the dichotomy of Gaussian and non-Gaussian clusters (measured by the AD test), we show that the probability of being a non-Gaussian cluster correlates significantly with X-ray asymmetry but only shows a marginal correlation with centroid shift. These results confirm the shape of the radial velocity distribution as a useful proxy for cluster relaxation, which can then be applied to large redshift surveys lacking extensive X-ray coverage.

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“…Current results suggest a strong link between the presence of diffuse intracluster radio emission and cluster mergers (Ferrari et al 2008;Feretti et al 2012, and references therein). Similar to what was done by Cassano et al (2010b), but using our set of X-ray morphological parameters, in this paper we analyse the X-ray morphology of relaxed clusters and nonrelaxed clusters (which includes both radio quiet and radio loud mergers).…”

Section: Introductionmentioning

confidence: 99%

Morphology parameters: substructure identification in X-ray galaxy clusters

Parekh

Heyden

Ferrari

et al. 2015

A&A

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Context. In recent years multi-wavelength observations have shown the presence of substructures related to merging events in a large proportion of galaxy clusters. Clusters can be roughly grouped into two categories -relaxed and non-relaxed -and a proper characterisation of the dynamical state of these systems is crucial for both astrophysical and cosmological studies. Aims. In this paper we investigate the use of a number of morphological parameters (Gini, M 20 , concentration, asymmetry, smoothness, ellipticity, and Gini of the second-order moment, G M ) introduced to automatically classify clusters as relaxed or dynamically disturbed systems. Methods. We apply our method to a sample of clusters at different redshifts extracted from the Chandra archive and investigate possible correlations between morphological parameters and other X-ray gas properties. Results. We conclude that a combination of the adopted parameters is a very useful tool for properly characterising the X-ray cluster morphology. According to our results, three parameters -Gini, M 20 , and concentration -are very promising for identifying cluster mergers. The Gini coefficient is a particularly powerful tool, especially at high redshift, because it is independent of the choice of the position of the cluster centre. We find that high Gini (>0.65), high concentration (>1.55), and low M 20 (<-2.0) values are associated with relaxed clusters, while low Gini (<0.4), low concentration (<1.0), and high M 20 (>-1.4) characterise dynamically perturbed systems. We also estimate the X-ray cluster morphological parameters in the case of radio loud clusters. Since they are in excellent agreement with previous analyses we confirm that diffuse intracluster radio sources are associated with major mergers.

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On the Connection Between Giant Radio Halos and Cluster Mergers

Cited by 320 publications

References 29 publications

Cosmology and astrophysics from relaxed galaxy clusters – I. Sample selection

Cosmology and astrophysics from relaxed galaxy clusters – I. Sample selection

Connecting optical and X-ray tracers of galaxy cluster relaxation

Morphology parameters: substructure identification in X-ray galaxy clusters

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