Rotation measures of radio sources in hot galaxy clusters

Govoni, F.; Dolag, K.; Murgia, M.; Feretti, L.; Schindler, S.; Giovannini, G.; Boschin, W.; Vacca, V.; Bonafede, A.

doi:10.1051/0004-6361/200913665

Cited by 82 publications

(117 citation statements)

References 90 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…On the other hand, no correlation seems to be present between the central magnetic field and the mean cluster temperature, in agreement with what found by Govoni et al (2010) in a statistical analysis of a sample of RM in rich galaxy clusters.…”

Section: D Simulationssupporting

confidence: 89%

See 1 more Smart Citation

Sardinia Radio Telescope observations of Abell 194

Govoni

Murgia

Vacca

et al. 2017

A&A

Self Cite

View full text Add to dashboard Cite

Aims. We study the intra-cluster magnetic field in the poor galaxy cluster Abell 194 by complementing radio data, at different frequencies, with data in the optical and X-ray bands. Methods. We analyze new total intensity and polarization observations of Abell 194 obtained with the Sardinia Radio Telescope (SRT). We use the SRT data in combination with archival Very Large Array observations to derive both the spectral aging and Rotation Measure (RM) images of the radio galaxies 3C 40A and 3C 40B embedded in Abell 194. To obtain new additional insights in the cluster structure we investigate the redshifts of 1893 galaxies, resulting in a sample of 143 fiducial cluster members. We analyze the available ROSAT and Chandra observations to measure the electron density profile of the galaxy cluster.Results. The optical analysis indicates that Abell 194 does not show a major and recent cluster merger, but rather agrees with a scenario of accretion of small groups, mainly along the NE-SW direction. Under the minimum energy assumption, the lifetimes of synchrotron electrons in 3C40 B measured from the spectral break are found to be 157±11 Myrs. The break frequency image and the electron density profile inferred from the X-ray emission are used in combination with the RM data to constrain the intra-cluster magnetic field power spectrum. By assuming a Kolmogorov power law power spectrum with a minimum scale of fluctuations of Λ min = 1 kpc, we find that the RM data in Abell 194 are well described by a magnetic field with a maximum scale of fluctuations of Λ max = (64 ± 24) kpc. We find a central magnetic field strength of B 0 = (1.5 ± 0.2) µG, the lowest ever measured so far in galaxy clusters based on Faraday rotation analysis. Further out, the field decreases with the radius following the gas density to the power of η=1.1±0.2. Comparing Abell 194 with a small sample of galaxy clusters, there is a hint of a trend between central electron densities and magnetic field strengths.

show abstract

Section: D Simulationssupporting

confidence: 89%

“…NGC 6251, 3C 449, NGC 383, (Perley et al 1984, but are much smaller in amplitude than in rich galaxy clusters (e.g. Govoni et al 2010). …”

Section: Polarization Results Summarymentioning

confidence: 89%

Sardinia Radio Telescope observations of Abell 194

Govoni

Murgia

Vacca

et al. 2017

A&A

Self Cite

View full text Add to dashboard Cite

show abstract

“…We further assume that the detected depolarization occurrs in the ICM, meaning neither eventual depolarization internal to the radio-sources nor in their immediate surroundings yield a dominant contribution (see Govoni et al 2006;Laing et al 2008;Bonafede et al 2010;Govoni et al 2010). The observed trend indicates that magnetic fields are common constituents of galaxy clusters, in agreement with the results by Clarke (2004) and Johnston-Hollitt et al (2004), who analyzed the Faraday rotation measures of sources located behind and within clusters.…”

Section: Fractional Polarization Trendsupporting

confidence: 84%

“…For example, magnetic fields of several μG were inferred in clusters without radio halo by e.g. Clarke et al (2001), and Murgia et al (2004), and recently, Govoni et al (2010) found that clusters seem to follow a common S X − RM distribution, S X being the X-ray surface brightness, independently on their radio properties. However, this is the first time that a statistical comparison between magnetic fields in clusters with and without radio emission has been performed and our result is a further indication that hadronic models are difficult to reconcile with present data (Brunetti et al 2008;and Dallacasa et al 2009;Donnert et al 2010;Jeltema & Profumo 2010).…”

Section: Magnetic Field and Radio Halo Originmentioning

confidence: 99%

“…Recently Govoni et al (2010) have analyzed the Faraday RM of a sample of sources that belong to hot nearby galaxy clusters, and used these data together with literature ones in order to investigate a possible connection between the magnetic field strength and the cluster mean temperature. Clusters are divided into three samples having T < 4 keV, 4 ≤ T ≤ 8 keV and T > 8 keV.…”

Section: Magnetic Field Strength and Cluster Temperaturementioning

confidence: 99%

See 1 more Smart Citation

Fractional polarization as a probe of magnetic fields in the intra-cluster medium

Bonafede

Govoni

Feretti

et al. 2011

A&A

Self Cite

View full text Add to dashboard Cite

Context. It is now established that magnetic fields are present in the intra-cluster medium (ICM) of galaxy clusters, as revealed by observations of radio halos and radio relics and from the study of the Faraday rotation measures of sources located either behind or within clusters. Deep radio polarization observations of clusters have been performed in the last years, and the properties of the ICM magnetic field have been constrained in a small number of well-studied objects. Aims. The aim of this work is to investigate the average properties of the ICM magnetic fields, and to search for possible correlations with the ICM thermal properties and cluster radio emission. Methods. We have selected a sample of 39 massive galaxy clusters from the HIghest X-ray FLUx Galaxy Cluster Sample, and used Northern VLA Sky Survey data to analyze the fractional polarization of radio sources out to 10 core radii from the cluster centers. We have investigated how different magnetic field strengths affect the observed polarized emission of sources lying at different projected distances from the cluster center. In addition, statistical tests are performed to investigate the fractional polarization trends in clusters with different thermal and non-thermal properties. Results. We find a trend of the fractional polarization with the cluster impact parameter, with fractional polarization increasing at the cluster periphery and decreasing toward the cluster center. Such trend can be reproduced by a magnetic field model with central value of few μG. The logrank statistical test indicates that there are no differences in the depolarization trend observed in cluster with and without radio halo, while the same test indicates significant differences when the depolarization trend of sources in clusters with and without cool core are compared. The comparison between clusters with high and low temperatures does not yields significant differences. Although the role of the gas density should be better accounted for, these results give important indications for models that require a role of the ICM magnetic field to explain the presence of cool core and radio halos in galaxy clusters.

show abstract

AGN feedback in clusters: Shock and sound heating

Nulsen¹,

McNamara²

2013

Astron Nachr

View full text Add to dashboard Cite

AGN feedback is now widely believed to play a crucial role in the co-evolution between the central black hole and its host galaxy. Two feedback modes have been identified, namely the radiative and kinetic modes, which correspond to the luminous AGNs and low-luminosity AGNs (LLAGNs), respectively. In this paper, we investigate the radiative heating in the kinetic mode. This process is potentially important because: 1) the radiation power of LLAGNs is higher than the jet power over a wide parameter range; 2) the spectral energy distribution of LLAGNs is such that the radiative heating is more effective compared to that of luminous AGNs with the same luminosity; and 3) most of the time in the lifecycle of an AGN is spent in the LLAGNs phase. In this paper, adopting the characteristic broad-band spectral energy distributions of LLAGNs, we calculate the value of "Compton temperature" (T C), which determines the radiative heating by Compton scattering. We find that T C ∼ (5 − 15) × 10 7 K, depending on the spectrum of individual LLAGN and at which distance from the black hole we evaluate the heating. We also compare this heating process with other radiative heating and cooling processes such as photoionization/recombination. Our result can be used for an accurate calculation of the radiative heating in the study of AGN feedback.

show abstract

Rotation measures of radio sources in hot galaxy clusters

Cited by 82 publications

References 90 publications

Sardinia Radio Telescope observations of Abell 194

Sardinia Radio Telescope observations of Abell 194

Fractional polarization as a probe of magnetic fields in the intra-cluster medium

AGN feedback in clusters: Shock and sound heating

Contact Info

Product

Resources

About