784 research outputs found

    Radio mini-halos and AGN heating in cool core clusters of galaxies

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    The brightest cluster galaxy (BCG) in the majority of relaxed, cool core galaxy clusters is radio loud, showing non-thermal radio jets and lobes ejected by the central active galactic nucleus (AGN). Such relativistic plasma has been unambiguously shown to interact with the surrounding thermal intra-cluster medium (ICM) thanks to spectacular images where the lobe radio emission is observed to fill the cavities in the X-ray-emitting gas. This `radio-mode AGN feedback' phenomenon, which is thought to quench cooling flows, is widespread and is critical to understand the physics of the inner regions of galaxy clusters and the properties of the central BCG. At the same time, mechanically-powerful AGN are likely to drive turbulence in the central ICM which may contribute to gas heating and also play a role for the origin of non-thermal emission on cluster-scales. Diffuse non-thermal emission has been observed in a number of cool core clusters in the form of a radio mini-halo surrounding the radio-loud BCG on scales comparable to that of the cooling region. This contribution outlines the main points covered by the talk on these topics. In particular, after summarizing the cooling flow regulation by AGN heating and the non-thermal emission from cool core clusters, we present a recent study of the largest collection of known mini-halo clusters (~ 20 objects) which investigated the scenario of a common origin of radio mini-halos and gas heating. We further discuss the prospects offered by future radio surveys with the Square Kilometre Array (SKA) for building large (>> 100 objects), unbiased mini-halo samples while probing at the same time the presence of radio-AGN feedback in the host clusters.Comment: 8 pages, 3 figures. Conference proceeding of "The many facets of extragalactic radio surveys: towards new scientific challenges", 20-23 October 2015, Bologna, Ital

    Discovery of diffuse radio emission at the center of the most X-ray-luminous cluster RX J1347.5-1145

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    We report on new VLA radio observations of the distant cluster RX J1347.5-1145, which is the most luminous in X-rays. We aim at investigating the possible presence of diffuse and extended radio emission in this very peculiar system which shows both a massive cooling flow and merging signatures. New low resolution (~18 arcsec) VLA radio observations of this cluster are combined with higher resolution (~2 arcsec) data available in the VLA archive. We discover the presence of a diffuse and extended (~500 kpc) radio source centered on the cluster, unrelated to the radio emission of the central AGN. The properties of the radio source, in particular a) its occurrence at the center of a massive cooling flow cluster, b) its total size comparable to that of the cooling region, c) its agreement with the observational trend between radio luminosity and cooling flow power, indicate that RX J1347.5-1145 hosts a radio mini-halo. We suggest that the radio emission of this mini-halo, which is the most distant object of its class discovered up to now, is due to electron re-acceleration triggered by the central cooling flow. However, we also note that the morphology of the diffuse radio emission shows an elongation coincident with the position of a hot subclump detected in X-rays, thus suggesting that additional energy for the electron re-acceleration might be provided by the submerger event.Comment: 5 pages, 6 figures, accepted for publication in A&A Letter

    Multifrequency VLA radio observations of the X-ray cavity cluster of galaxies RBS797: evidence of differently oriented jets

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    We report on the peculiar activity of the radio source located at the center of the cooling flow cluster RBS797 (z=0.35), the first distant cluster in which two pronounced X-ray cavities have been discovered. New multifrequency (1.4, 4.8, and 8.4 GHz) observations obtained with the Very Large Array clearly reveal the presence of radio emission on three different scales showing orientation in different directions, all of which indicates that RBS797 represents a very peculiar case. The lowest resolution images show large-scale radio emission characterized by amorphous morphology and a steep spectrum, extended on a scale of hundreds of kpc. On a scale of tens of kpc, there is evidence of 1.4 GHz radio emission elongated in the northeast-southwest direction exactly towards the holes detected in X-rays. The highest resolution image shows the details of the innermost 4.8 GHz radio jets on a kpc scale; they are remarkably oriented in a direction that is perpendicular to that of the extended structure detected at a lower resolution. We therefore find evidence of a strong interaction between the central radio source and the intra-cluster medium in RBS797. We suggest a scenario in which the 1.4 GHz emission filling the X-ray cavities consists of buoyant bubbles of radio emitting plasma that are created by twin jets in the past and whose expansion has displaced the thermal gas that was formerly in the X-ray holes, whereas the two jets visible at 4.8 GHz are related to the present nuclear activity that has restarted at a different position angle from the original outburst that created the outer radio lobes. The total radio luminosity is ~ 10^42 erg/s, corresponding to a factor of a few thousand times less than the estimated cooling luminosity.Comment: 9 pages, 4 figures, accepted for publication in Astronomy & Astrophysics; replaced with revised version corrected for language editin

    On the connection between radio mini-halos and gas heating in cool core clusters

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    In this work, we present a study of the central regions of cool-core clusters hosting radio mini-halos, which are di use synchrotron sources extended on cluster-scales surrounding the radio-loud brightest galaxy. We aim to investigate the interplay between the thermal and non-thermal components in the intracluster medium in order to get more insights into these radio sources, whose nature is still unclear. It has recently been proposed that turbulence plays a role for heating the gas in cool cores. A correlation between the radio luminosity of mini-halos, νPν\nu P_{\nu}, and the cooling flow power, PCFP_{\rm CF}, is expected in the case that this turbulence also plays a role for the acceleration of the relativistic particles. We carried out a homogeneous re-analysis of X-ray Chandra data of the largest sample of cool-core clusters hosting radio mini-halos currently available (∼20\sim20 objects), finding a quasi-linear correlation, νPν∝PCF0.8\nu P_{\nu} \propto P_{\rm CF}^{0.8}. We show that the scenario of a common origin of radio mini-halos and gas heating in cool-core clusters is energetically viable, provided that mini-halos trace regions where the magnetic field strength is B≫0.5μGB \gg 0.5 \mu G.Comment: 4 pages, 2 figures. Conference proceeding of "The many facets of extragalactic radio surveys: towards new scientific challenges", 20-23 October 2015, Bologna, Ital

    The complex galaxy cluster Abell 514: New results obtained with the XMM - Newton satellite

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    We study the X-ray morphology and dynamics of the galaxy cluster Abell 514. Also, the relation between the X-ray properties and Faraday Rotation measures of this cluster are investigated in order to study the connection of magnetic fields and the intra-cluster medium. We use two combined XMM - Newton pointings that are split into three distinct observations. The data allow us to evaluate the overall cluster properties like temperature and metallicity with high accuracy. Additionally, a temperature map and the metallicity distribution are computed, which are used to study the dynamical state of the cluster in detail. Abell 514 represents an interesting merger cluster with many substructures visible in the X-ray image and in the temperature and abundance distributions. The new XMM - Newton data of Abell 514 confirm the relation between the X-ray brightness and the sigma of the Rotation Measure (S_X - sigma_RM relation) proposed by Dolag et al. (2001).Comment: 9 pages, 13 figures, accepted for publication in A&

    Radio-continuum surveys with SKA and LOFAR: a first look at the perspectives for radio mini-halos

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    Diffuse synchrotron radio emission has been observed in a number of cool-core clusters on scales comparable to that of the cooling region. These radio sources are called `mini-halos'. In order to understand their origin, which is still unclear, joint radio and X-ray statistical studies of large cluster samples are necessary to investigate the radio mini-halo properties and their connection with the cluster thermodynamics. We here extend our previous explorative study and investigate the perspectives offered by surveys in the radio continuum with LOFAR and SKA, in particular examining the effect of the intra-cluster magnetic field in the mini-halo region for the first time. By considering the minimum flux detectable in radio surveys and exploiting the Pradio−LXP_{radio}-L_X correlation observed for known mini-halos, we estimate the detection limits achievable by future radio observational follow-up of X-ray cluster samples, such as HIFLUGCS and eROSITA. This allows us to estimate the maximum number of radio mini-halos that can potentially be discovered in future surveys as a function of redshift and magnetic field strength. We show that future radio surveys with LOFAR and SKA1 (at 140 MHz and 1.4 GHz) have the potential to discover ~1,000-10,000 radio mini-halo candidates up to redshift z=1. We further note that future SKA1 radio surveys at redshift z>0.6 will allow us to distinguish between different magnetic fields in the mini-halo region, because higher magnetic fields are expected to produce more powerful mini-halos, thus implying a larger number of mini-halo detected at high redshift. For example, the non-detection with SKA1 of mini-halos at z>0.6 will suggest a low magnetic field (B < few μ\muG). The synergy of these radio surveys with future X-ray observations and theoretical studies is essential in establishing the radio mini-halo physical nature. [abridged]Comment: Accepted for publication in A&A; 9 pages, 9 figures. Revised to match the corrected version after language editin
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