The Extended GMRT Radio Halo Survey I: New upper limits on radio halos and mini-halos
R. Kale, T. Venturi, S. Giacintucci, D. Dallacasa, R. Cassano, G. Brunetti, G. Macario, R. Athreya
aa r X i v : . [ a s t r o - ph . C O ] J un Astronomy&Astrophysicsmanuscript no. kale˙egrhs1 c (cid:13)
ESO 2018October 30, 2018
The Extended GMRT Radio Halo Survey I: New upper limits onradio halos and mini-halos
R. Kale , , T.Venturi , S. Giacintucci , , D. Dallacasa , , R. Cassano , G. Brunetti , G. Macario , R. Athreya Dipartimento di Fisica e Astronomia, Universita di Bologna, via Ranzani 1, 40126 Bologna, Italye-mail: [email protected] INAF-Istituto di Radioastronomia, via Gobetti 101, 40129 Bologna, Italy Department of Astronomy, University of Maryland, College Park, MD 20742, USA Joint Space-Science Institute, University of Maryland, College Park, MD, 20742-2421, USA Laboratoire Lagrange, UMR7293, Universite de Nice Sophia-Antipolis, CNRS, Observatoire de la Cote dAzur, 06300 Nice, France Indian Institute of Science Education and Research (IISER), Pune, Indiasubmitted to AA
ABSTRACT
Context.
A fraction of galaxy clusters host di ff use radio sources called radio halos, radio relics and mini-halos. These are associatedwith the relativistic electrons and magnetic fields present over ∼ Mpc scales in the intra-cluster medium.
Aims.
We aim to carry out a systematic radio survey of all luminous galaxy clusters selected from the REFLEX and eBCS X-raycatalogs with the Giant Metrewave Radio Telescope, to understand the statistical properties of the di ff use radio emission in galaxyclusters. Methods.
We present the sample and first results from the Extended GMRT Radio Halo Survey (EGRHS), which is an extension ofthe GMRT Radio Halo Survey (GRHS, Venturi et al. 2007, 2008).
Results.
Analysis of radio data at 610 / /
325 MHz on 12 galaxy clusters are presented. We report the detection of a newlydiscovered mini-halo in the cluster RXJ1532.9 + ∼
200 kpc) is suspected inthe cluster Z348. We do not detect cluster-scale di ff use emission in 11 clusters. Robust upper limits on the detection of radio halo ofsize of 1 Mpc are determined. We also present upper limits on the detections of mini-halos in a sub-sample of cool-core clusters. Theupper limits for radio halos and mini-halos are plotted in the radio power- X-ray luminosity plane and the correlations are discussed.Di ff use extended emission, not related to the target clusters, but detected as by-products in the sensitive images of two of the clusterfields (A689 and RXJ0439.0 + Conclusions.
Based on the information about the presence of radio halos (or upper limits), available on 48 clusters out of the totalsample of 67 clusters (EGRHS + GRHS), we find that 23 ±
7% of the clusters host radio halos. The radio halo fraction rises to 31 ± > × erg s − are considered. Mini-halos are found in ∼
50% of cool-core clusters.A qualitative examination of the X-ray images of the clusters with no di ff use radio emission indicates that a majority of these clustersdo not show extreme dynamical disturbances and supports the idea that mergers play an important role in the generation of radiohalos / relics. The analysis of the full sample will be presented in a future work. Key words. radio continuum:galaxies–galaxies:clusters:general
1. Introduction
Galaxy clusters are massive ( ∼ − M ⊙ ) assemblies ofdark matter, di ff use gas and galaxies. The di ff use gas, called theintra-cluster medium (ICM), mainly consists of hot thermal gas( ∼ − K). It emits thermal Bremsstrahlung radiation andis detected in X-rays. Relativistic particles (with Lorentz factors γ > ∼ . − µ G) are mixed with thethermal gas. The synchrotron emission associated with the ICM,detectable in the radio band, is a direct probe of the relativisticelectrons and magnetic fields.The radio emission from the ICM has been classified intothree main types: radio halos, radio relics and mini-halos (seeFeretti et al. 2012, for a review). Radio halos are ∼ Mpc sizedsources having synchrotron spectra with typical spectral in-dices, α ∼ . − . ff useradio sources at cluster peripheries, typically with filamentary, S ∝ ν − α , where S is the flux density at frequency ν and α is thespectral index. arc-like or irregular morphologies. Relics are also highly polar-ized and can have sizes in the range 0.2 to 2 Mpc. Mini-halosare 150 – 500 kpc in size and have been found around dominantradio galaxies at cluster centers.Radio relics having elongated or arc-like morphologies thatare located at cluster peripheries, have been proposed to be pro-duced by electrons that are accelerated by merger or accretionshocks (Enßlin et al. 1998). In some cases, the polarization prop-erties and the spectral steepening from outer to inner edges havebeen observed which confirms their connection with the out-going cluster merger shock waves (e.g. Giacintucci et al. 2008;van Weeren et al. 2010; Kale et al. 2012). The Mach numbers ofthe shocks have been estimated to be in the range ∼ − ffi cient in accelerating electrons tothe observed energies and the acceleration mechanism behindrelics is still not understood (see Markevitch 2010; Jones 2012;Kang et al. 2012; Pinzke et al. 2013). The origin of radio halos and mini-halos is still a matter ofdebate. The long di ff usion times of the relativistic electrons com-pared to their short radiative lifetimes require an in-situ mech-anism of generation of relativistic electrons in the ICM (Ja ff e1977).Mini-halos have been found in relaxed, cool core clusters (e.g.Gitti et al. 2002; Govoni et al. 2009; Giacintucci et al. 2011).Re-acceleration of a pre-existing population of relativistic elec-trons in cool cores by turbulence has been proposed to explainthe mini-halos (Gitti et al. 2002; Mazzotta & Giacintucci 2008;ZuHone et al. 2013). The origin of turbulence in the ICM of coolcore clusters is still unclear, however it might be generated bygas sloshing (Mazzotta & Giacintucci 2008). The seed relativis-tic electrons may be injected from the activity of central AGN(e.g. Cassano et al. 2008) and / or may be secondary products ofhadronic collisions in the ICM (e.g. Pfrommer & Enßlin 2004;Keshet & Loeb 2010).In the case of radio halos, there are two main classes of theoreti-cal models, namely, the ‘secondary electron’ models and the tur-bulent re-acceleration based models. According to the secondaryelectron models, the relativistic electrons which are produced assecondary products of the hadronic collisions in the ICM, in thepresence of magnetic fields lead to the generation of sources likeradio halos (e.g. Dennison 1980; Blasi & Colafrancesco 1999;Dolag & Enßlin 2000; Keshet & Loeb 2010). The gamma raysexpected from the hadronic collisions in the ICM have so far notbeen detected and this poses a challenge to the secondary elec-tron models (e.g. Jeltema & Profumo 2011; Ackermann et al.2010; Brunetti et al. 2012).In the turbulent re-acceleration based models, it is proposed thata low energy relativistic electron population in the ICM is re-accelerated by turbulence injected by mergers (Brunetti et al.2001; Petrosian 2001; Petrosian & East 2008). The seed elec-tron population can be primary and / or secondary in origin. Theexpectations of these models, such as the occurrences of radiohalos in luminous, massive and merging clusters, have receivedsupport from the observations (e.g. Buote 2001; Cassano et al.2010). According to these models the most powerful radio ha-los are likely to occur in the energetic mergers involving verymassive galaxy clusters. A population of radio halos generatedin lower energy cluster mergers (more common), with a char-acteristic very steep synchrotron spectrum ( α ≥ .
5) due tolower energy in turbulence, is also predicted (e.g. Cassano et al.2006). These low energy radio halos are termed as ultra-steepspectrum radio halos (USSRHs) and a few have been detectedso far (e.g. Brunetti et al. 2008; Macario et al. 2010, 2013). Dueto their steep spectra, instruments operating at low frequenciessuch as the GMRT and the LOFAR are favoured for detecting theUSSRHs. The existence of the USSRHs is also a challenge forthe secondary models that would require uncomparably large en-ergy content in cosmic ray protons (see Brunetti et al. 2008, andreferences therein). Consequently LOFAR may allow a comple-mentary test on the origin of radio halos.One of the most promising ways to make progress in theunderstanding of these sources is to observe a large numberof clusters to obtain statistics of the occurrence of radio halos,relics and mini-halos. The success of this approach is evidentfrom the results of the GMRT Radio Halo Survey (hereafterGRHS) (Venturi et al. 2007, 2008, hereafter, V07 and V08 re-spectively). The GRHS led to the discoveries of 4 radio halos,1 mini-halo and 3 di ff use radio relic / halo candidates in galaxyclusters. Most importantly GRHS also gave the first upper limitson the detections of radio halos using the method of model ra-dio halo injection. The understanding of empirical correlations between the radio power at 1.4 GHz of the halo (P . ) andX-ray luminosity (L X ) of the parent cluster and the connectionbetween cluster mergers and radio halos have been significantlyimproved with the inclusion of upper limits. A limit on the life-time of a radio halo using the bimodal distribution of radio haloand non-radio-halo clusters in the P . –L X plane was obtained(Brunetti et al. 2007). The first quantitative estimate of the sep-aration of radio halo and non-radio halo clusters as merging andnon-merging clusters has been made using the GRHS and theChandra data (Cassano et al. 2010). Recently, using the mea-surements of integrated Compton Y parameter of clusters withthe Planck satellite, a scaling between radio halo power and Yhas been presented which shows a weaker bimodality as com-pared to that in the P . –L X plane (Basu 2012). However, itis essential to improve the statistical significance of these rela-tions to better understand the connection between the thermaland non-thermal components (relativistic electrons and magneticfields) of the ICM.With this motivation we have undertaken the ExtendedGMRT Radio Halo Survey (EGRHS). In this paper we presentthe first results from the EGRHS. The EGRHS sample is de-scribed in Sec. 2. The radio observations and data reduction aredescribed in Sec. 3. The results based on the radio images arepresented in Sec. 4. The estimates of the upper limits are pre-sented in Sec. 5. The results are discussed in Sec. 6 and a sum-mary is presented in Sec. 7. Radio images of each of the clusterfields covering a region up to the virial radius are presented inAppendix 1.A cosmology with H =
70 km s − Mpc − , Ω m = . Ω Λ = .
2. The Extended GMRT Radio Halo Survey
The EGRHS consists of a galaxy cluster sample extractedfrom the ROSAT-ESO Flux Limited X-ray galaxy cluster cat-alog (REFLEX, B¨ohringer et al. 2004) and from the extendedROSAT Brightest Cluster Sample catalog (eBCS, Ebeling et al.1998, 2000). The selection criteria are :1. L X (0.1-2.4 keV) > × erg s − ;2. 0 . < z < . δ > − ◦ for the REFLEX and eBCS samples.The declination limit, imposed while selecting clusters fromthe eBCS catalog for the GRHS sample is extended to obtainthe EGRHS sample. The choice of high X-ray luminosity en-sures that the radio halos (if present, and with radio powersexpected from the P . -L X scaling) will be well within thedetection limits of the GMRT. The X-ray luminosity and theredshift ranges also ensure higher possibility of the occurrenceof radio halos based on model predictions (Cassano et al. 2004;Cassano & Brunetti 2005; Cassano et al. 2006). The lower limitin declination of − ◦ will ensure good uv- coverage with theGMRT. These selection criteria led to a sample of 67 clusters.Of these 50 clusters were part of the GRHS (V07, V08) and theadditional 17 form the EGRHS (Table 1).
3. Radio observations and data reduction
The aim of the EGRHS and GRHS together is to assemble alarge sample of galaxy clusters with sensitive radio observationsin order to improve the statistical information on radio halos,relics and mini-halos. Therefore along with new observations forEGRHS, we are also carrying out observations of a few GRHS clusters for which radio data were inadequate (Table 1). Here weprovide a summary of what is presented in this paper: – – – archival 325 MHz GMRT observations for 3 clusters inthe GRHS (GMRT Cluster Key Science project, PI V. K.Kulkarni) and – a re-analysis of 610 MHz data from V08 on the GRHS clus-ter RXJ1532.9 + ff use emission at an-other frequency. Secondly, the low frequency (235 MHz) allowsfor a possibility of the detection of USSRHs. In EGRHS eachcluster is observed for an 8 hour duration in the dual frequencymode. This has resulted in better uv- coverage as compared tothe GRHS. Thus the EGRHS is an extension of GRHS with anupgraded observing strategy.The dual frequency observations of the EGRHS were car-ried out with the GMRT Software Backend (Roy et al. 2010)in the mode that provided 256 channels to acquire the data.Bandwidths of 32 MHz at 610 MHz and 8 MHz at 235 MHzwere used.Data were analysed using the NRAO Astronomical ImageProcessing System (AIPS). The steps in data reduction that werefollowed at both 610 and 235 MHz are described briefly. Thedata from the antennas that were not working were identified byexamining the calibrators and removed. The task ‘SPFLG’ wasused to identify and remove the channels a ff ected by radio fre-quency interference. The channels at the edges of the bands werealso removed due to lower sensitivity and stability. After excis-ing bad data, calibration using the primary and secondary cal-ibrators was carried out. The calibrated data were re-examinedand any remaining bad data were excised. The edited and cal-ibrated data on target source were then averaged in frequencyto an extent which kept ‘bandwidth smearing’ e ff ect at negligi-ble levels. The data were then imaged using wide field imag-ing technique. Several iterations of phase-only self-calibrationand a final amplitude and phase self-calibration were carried outto improve the sensitivities of the images. Various tapers andweighting schemes on the uv-data were used to make imageswith a wide range of synthesized beams. Images with resolu-tions (FWHM) 4 ′′ − ′′ and 10 ′′ − ′′ at 610 and 235 MHz,respectively, were examined. These were used in combinationwith high resolution images to test the presence of any suspectedextended emission.For two EGRHS clusters, Z348 and A267, and for the GRHScluster A2261 dual frequency data were recorded with the hard-ware backend. It provided single polarization (RR) in two side-bands with 128 channels and a bandwidth of 16 MHz each at610 MHz. The 235 MHz data were recorded simultaneously in aseparate polarization (LL) in a single sideband with a bandwidthof 8 MHz. The data were analysed separately for each sidebandand the images were then combined. In addition to these we alsoreanalysed the 610 MHz data on RXJ1532.9 + +
4. Results
The analysis of these data have led to sensitive radio images ofthe 12 galaxy clusters. Radio images with rms noise in the range45 - 80 µ Jy beam − at 610 MHz, 0.25 - 0.4 mJy beam − at 325MHz and 0.45 - 1.8 mJy beam − at 235 MHz were obtained(Table 2). These are consistent with the sensitivities obtained inthe GRHS and thus ensure the uniformity of the survey.The main results of the paper are as follows. We presentthe 610 MHz image of the newly detected mini-halo in thecluster RXJ1532.9 + ff use emis-sion on smaller scales ( <
250 kpc) are suspected in Z348 andRXCJ0437.1 + The sensitivities achieved using ‘natural weights’ (robust = ∼
5% at 610 MHz (e.g.Chandra et al. 2004) and ∼ −
15% at 325 and 235 MHz.The radio images obtained using natural weights for the uv -data(610 /
325 MHz) of central regions of the clusters are shown incontours overlayed on the Chandra / XMM Newton X-ray im-ages shown in colour in Fig. 1. Radio images of all the clus-ters covering regions up to the virial radius are presented inAppendix 1. A short note on each of the clusters based on ourradio images and the information available in the literature ispresented below.
The cluster A1576 (RXC J1236.9 + R =
3) at a redshift of 0.302 (1 ′′ = .
50 kpc). The radioimage shows the presence of a central radio galaxy, almost coin-cident with the peak in the X-ray emission (Fig. 1). In the high-est resolution 610 MHz image (not shown), the central sourceresolves into at least 2 components which are coincident withoptically detected galaxies in A1576. The optical counterpart ofthis radio galaxy has at least three optically detected nuclei andis suspected to be in an advanced stage of merger (Dahle et al.2002). The central source has a jet-like extension toward thenorthwest. The slight extension toward northeast may be an arte-fact. The two other radio sources visible in the A1576 fieldshown in Fig. 1 have optical counterparts and are possibly ra-dio galaxies in the cluster.The field of this cluster contains several radio sources(Fig. A.1). About 3 ′ west of cluster center is a double lobed ra-dio galaxy. The core of this galaxy is not detected in the 610and 235 MHz radio images and also in the FIRST survey. Thusthe optical counterpart for this radio galaxy is not obvious. Themorphology of the lobes indicates that it is of FR-II type. The Data from Chandra observation IDs 7938, 10415, 9369, 3583,10440, 3580, 10465, 11729, 10439 and XMM Newton observationnumber 0652010201 are used. 3ale et al.: The Extended GMRT Radio Halo Survey I
Fig. 1.
Radio images (contours) are shown overlaid on X-ray images (colour) for the 11 galaxy clusters presented in this paper.The radio images are at 610 MHz for the clusters A1576, A689, RXJ0439.0 + + + + σ × ( ± , , , , ... ) (see Table 2 for 1 σ levels and the beam sizes). Positive contours are shown in black and negative in cyan.The exposure corrected Chandra (ACIS-I) images are presented for all clusters, except RXCJ1212.3-1816 for which XMM Newton(EPIC MOS) pipeline processed image is presented. The X-ray images are smoothed to resolutions of 10 ′′ − ′′ .spectral indices (235 - 610 MHz) of the eastern and the westernlobes are 0.65 and 0.72, respectively.Based on weak lensing analysis, Dahle et al. (2002) infer sig-nificant dynamical activity in A1576. The X-ray surface bright-ness distribution is elongated in the east-west direction and does not show pronounced central peak (Fig. 1). The cluster is rel-atively hot, with a temperature of 8.65 keV (Cavagnolo et al.2009). A689 (RX J0837.4 + ′′ = .
26 kpc) with richness, R =
0. There is a bright X-ray andradio source associated with the central AGN in A689 (Fig. 1).The positive and negative emission at ∼ σ level, surroundingthe bright central source are noise structures. The radio imageof A689 contains several bright sources (Fig. A.2). In particu-lar there is a complex blend of radio galaxies and a low sur-face brightness feature toward the southeast of the cluster center(Fig. A.2, see Sec. 4.2.2).Prominent sub-structures have been reported in the massdistribution derived from lensing measurements (Okabe et al.2010). RXJ0439.0 + ′′ = .
41 kpc). There is a radio source at the center and anothersource toward its south, possibly a head-tail galaxy (Fig. 1). Thecentral source has some hint of extended emission (on ∼
50 kpcscale), but needs higher resolution observations to confirm it.About 4 ′ east of the center, a possible FR-I type radio galaxy isseen (Fig. A.3). A bright radio galaxy with a distinct core andtwo extended lobes with hot spots is detected about 9 . ′ westof the center (Fig. A.3). Optical counterparts to both these radiogalaxies are detected in DSS POSS-II images. However, theirconnection to the galaxy cluster is unclear due to unavailabilityof redshifts for the optical counterparts.The cluster has a temperature of 4.63 keV (Cavagnolo et al.2009) and a circularly symmetric morphology in X-rays(Jeltema et al. 2005) (Fig. 1). This implies that this cluster ismost likely relaxed, with no recent dynamical activity. The cluster RXJ0439.0 + ′′ = .
86 kpc). A weak radio source is coincident with the peakin the X-rays (Fig. 1). Adjacent to this source is a bright radiosource that resolves into a double source, oriented in the north-south direction, in the high resolution image at 610 MHz (notshown). In the cluster field up to the virial radius, a bright radiogalaxy ∼ ′ north-west of the cluster center is seen (Fig. A.4).A pattern due to improper deconvolution of this bright sourceis visible in Fig. A.4. The tail-like extension of the radio source,just south of the cluster center is most likely a part of this pattern.The cluster is elliptical and elongated along north-south di-rection in X-rays (Fig. 1). The cluster has a temperature of 6.5keV (Cavagnolo et al. 2009). There is no information about thedynamical state of this cluster in the literature. RXJ0142.0 + ′′ = . ±
134 km s − , however, nosubstructure in the velocity distribution (Barr et al. 2005). Basedon the mass-to-light ratios of galaxies and α − element abundanceratios, a possibility of a past merger in the cluster has been in-ferred (Barr et al. 2006). The cluster A267 is at a redshift of 0.230 (1 ′′ = .
69 kpc) withrichness, R =
0. A faint radio source is detected at the center ofthis cluster (Fig. 1). The cluster field has some compact brightradio sources (Fig. A.6).The cluster has a cD galaxy at the center (Dahle et al.2002) and the X-ray distribution is elliptical (Jeltema et al. 2005)(Fig. 1). The cluster is moderately hot with a temperature of8.7 keV (Cavagnolo et al. 2009). It has been classified as a coolcore cluster based on the analysis of power ratios (Bauer et al.2005). However, its temperature profile lacks the typical dropin the centers of cool-cores and it has a relatively high valueof central entropy (170 keV cm ; Cavagnolo et al. (2009)). Thiscentral entropy is much higher than 50 keV cm , which isthe value adopted to separate cool cores and non-cool cores(Cavagnolo et al. 2009; Rossetti et al. 2011). Therefore A267 islike a non-cool core based on its entropy and temperature, but arelaxed cluster based on the power ratios. Z348 (RXC J0106.8 + ′′ = . ∼ ′′ towardnorth, a di ff use source is detected in the 610 MHz image (Fig. 1).The source is elongated in the east-west direction and has anextent of ∼
200 kpc, if assumed to be at the redshift of Z348.It could be a relic of smaller extent similar to the one in A85(Slee et al. 2001). The nature of this source remains to be con-firmed.There is an AGN at the cluster center with strong X-ray emis-sion (B¨ohringer et al. 2000), which is also detected as a compactradio source (Fig. 1). The Chandra X-ray image shows ellipticaldistribution of emission along the northeast-southwest direction.No information about the dynamical status of Z348 is availablein the literature.
A2261 is a rich cluster ( R =
2) at a redshift of 0.224 (1 ′′ = . + ∼ . ′ =
540 kpc) toward thenorthwest of the cluster center. The radio galaxy shows pres-ence of a compact source at the center and di ff use emission ex-tended on two sides of it (Fig. 2). The di ff use emission is fil-amentary and of total extent ∼
590 kpc (if at the redshift ofthe cluster). Based on the morphology it is possibly an ‘FR-I’type radio galaxy. The total flux density (core + di ff use) of theradio galaxy at 610 MHz is 57 ± + + ff use radio emission was suspected in this cluster basedon the 1.4 GHz VLA D array image (V08). However, we did notfind cluster wide extended radio emission at 610 and 235 MHz.The cluster has circular morphology in X-rays and is mostlikely a relaxed system. It has a temperature of 7.58 keV(Cavagnolo et al. 2009). There is a di ff use patch of X-ray emis- sion, west of the cluster, however its connection to the cluster isunknown. The cluster RXCJ0437.1 + ′′ = .
31 kpc). There is a weak radio source at the cluster center andan elongated radio source to the north of it (Fig. 1). The extentof the elongated source in the east-west direction is ∼
256 kpc, ifassumed to be at the redshift of the cluster. These sources werealso detected at 1.4 GHz by Feretti et al. (2005). Their flux den-sities at 325 MHz are 4 . ± . ± − (beam = ′′ × ′′ , p. a. 23 ◦ ) at 1.4 GHz based on the 3 σ level inthe image was reported by Feretti et al. (2005). An upper limitusing the method of injection of radio halo is presented in thiswork (Sec. 5).This cluster field has other bright radio sources (Fig. A.9). Adouble radio galaxy is located ∼ . ′ east of the cluster center.The X-ray emission from the cluster appears elliptical andelongated, roughly in the north-south direction (Fig. 1). Thecluster has a temperature of 7-8 keV in the outer regionsand 5 keV at the center and is most likely a relaxed cluster(Feretti et al. 2005). RXCJ1212.3-1816 is at a redshift of 0.269 (1 ′′ = .
14 kpc).There is no radio source in the vicinity of the cluster center(Fig. 1). The cluster field shows a few bright radio sources(Fig. A.10).The cluster appears elongated in the northeast-southwest di-rection in the X-ray image with XMM Newton (Fig. 1). The mor-phology also hints at a disturbed ICM. There is no informationin the literature about the dynamical status of this cluster.
A2485 is at a redshift of 0.247 (1 ′′ = .
89 kpc). The 610 MHzdata on this cluster was presented in V08. However, it was notconsidered for analysis due to high rms noise (V08). Radio im-age at 325 MHz is presented here. There is no bright radio sourceclose to the cluster center (Fig. 1). The field up to virial radiusshows presence of several compact radio sources (Fig. A.11).The X-ray emission may be disturbed as the central peakis not pronounced (Fig. 1). There is no information about thedynamical status of this cluster in the literature.
The cluster RXJ1532.9 + ′′ = . ff use mini-halo around the central unresolved radio galaxy (marked S1). The flux den-sity of the mini-halo is ∼
16 mJy (after subtraction of the com-pact source S1, whose flux density is ∼
20 mJy) at 610 MHz.The largest linear size of ∼
200 kpc is detected at 610 MHz. Theproperties of this mini-halo will be reported in detail elsewhere(Giacintucci et al. in prep.).Based on the X-ray properties, this cluster is classified as acool core cluster (Hlavacek-Larrondo & Fabian 2011). It has anaverage temperature of 5.65 keV (Cavagnolo et al. 2009).
The EGRHS and the GRHS surveys are designed to be sensitiveto low surface brightness, extended features such as the radiohalos and relics. The resulting sensitive images thus also have thepotential to detect other kind of faint extended emission such assynchrotron emission from galaxies, faint portions of radio lobesor even relic lobes of radio galaxies. We present the detection ofsuch emission associated with galaxies found in the images ofthe clusters A689 and RXJ0439.0 + In the field of view of the cluster RXJ0439.0 + ∼ ′ eastof the center, a patch of di ff use emission was detected at 610 and235 MHz. The NVSS survey also detects this source, however,with a resolution of 45 ′′ , it is not resolved. Overlay of the ra-dio image on the Digitized Sky Survey R-band image revealedthe presence of the galaxy NGC1633 at location of the di ff usepatch (Fig. 4, left). NGC1633 is a spiral galaxy at a redshift of0.016642 (De Vaucouleurs et al. 1991, RC3.9). Since there isno compact source detected in higher resolution images madeat 610 and 235 MHz, this di ff use emission is most likely syn-chrotron emission from the disk of the galaxy. The largest linearsize of the emission detected at 610 MHz is ∼
16 kpc. The fluxdensities at 610 and 235 MHz estimated using primary beam cor-rected images are 13 . ± . . ± . ′ west of the center of this cluster field an-other interesting source was noticed. The NVSS sourceNVSSJ043652 + ± ± ff usesources are detected in the 235 MHz image. We propose thatthese are ‘lobes’ associated with the radio galaxy. The angularseparations of the ‘lobes’ from the core are 4 . ′ (eastern lobe)and 6 . ′ (western lobe). The eastern lobe is also detected in the610 MHz image. The western lobe is at the edge of the 610 MHzfield of view, in a region with poor sensitivity, and thus cannot bedetected. No jets connecting these lobes to the core are detected.These lobes are not detected in the NVSS due to their low bright-ness. The high resolution (uniform weighted) images at 610 and235 MHz resolve out the lobes, confirming their di ff use nature.There are no obvious optical or infra-red counterparts to these.The di ff use lobes, due to their locations relative to the centraldouble, are likely to be lobes of the radio galaxy, also possiblyfrom a previous activity. We did not find any identification orredshift information of the host galaxy. Fig. 2.
GMRT 610 MHz image of the central region of the clusterA2261 shown in contours overlayed on DSS POSS-II R bandoptical image shown in colour. The contour levels and the beamare the same as in Fig. 1. An optical source is coincident withthe central radio source and with the core of the radio galaxy.
Toward the southeast of the center of the field A689, two radiosources with complex morphologies were detected. A complexblend of radio sources and a filament of di ff use emission are de-tected ∼ ′ and ∼ ′ southeast of the cluster center, respectively(Figs. A.2).The complex blend of radio sources consists ofthree distinct radio galaxies (Fig. 5). A galaxy clusterWHLJ083744.3 + ff use emission further southeast of the radio galaxycomplex is detected in both 610 and 235 MHz images (Figs. 5,A.2). The source NVSS J083816 + ff use emission. A few galaxies are de-tected in the Sloan Digitized Sky Survey (SDSS) at the locationof the di ff use emission. It is possible that the di ff use emission is ablend of the emission from these individual galaxies. No redshiftinformation is available for the SDSS galaxies. Deeper radio ob-servations of this region are required to map the morphology ofthis emission. Determination of the redshifts of the galaxies inthis region will enable to estimate the linear extent of the di ff useemission.
5. Upper limits
Firm upper limits on the detections of radio halos in these clus-ters are an important part of this survey. With the non-detectionsof radio halos in the 11 clusters, we proceeded to the step ofdetermining the upper limits. We followed a procedure for plac-
Fig. 3.
GMRT 610 MHz image of RXJ1532.9 + − and increase by a factor 2. The beam is 5 . ′′ × . ′′ , p.a.82 ◦ . The rms noise and the beam in the grey-scale image are50 µ Jy beam − and 9 . ′′ × . ′′ , p.a. 69 ◦ respectively. A compactsource S1 is at the center and is surrounded by the mini-halo.ing firm upper limits on the flux density of extended emissionthat was used in the GRHS (Brunetti et al. 2007, V08). The pro-cedure consists of introducing simulated (fake) radio halos of agiven size and brightness in the uv- data and then re-imaging thedata. Use of radio images over a wide range of resolutions ismade in establishing the upper limit. The typical rms noise inlow resolution images is reported in Table 3. A fake radio halo of 1 Mpc diameter, which is the typical size ofgiant radio halos, was chosen for injection. It was modeled us-ing optically thin concentric spheres to match the average profileof well studied radio halos (Brunetti et al. 2007, V08). The task‘UVMOD’ was used to add the model to the uv- data. The new uv- data were used to make image and the detection of the fakeradio halo was examined in it. Fake radio halos with flux densi-ties at 610 MHz over a range of 3 - 20 mJy were injected in thedata sets. For those with data at 325 MHz the flux densities ofthe injected halos were scaled with a spectral index of 1 .
3. Theupper limits obtained on the detection of a 1 Mpc diameter radiohalo are listed in Table 3. Following the earlier works (V08), aspectral index of 1 . . – L X plane (blue and magenta arrows, Fig. 6). The old upper lim-its (black arrows), the giant radio halos (filled and open blackpoints) and the correlation line obtained from these giant ra-dio halos shown in the plot are reproduced from Brunetti et al.(2009). The red asterisks are the known ultra-steep spectrumgiant radio halos in the GRHS sample, namely, A697 (V08Macario et al. 2010), A521 (Brunetti et al. 2008; Dallacasa et al.2009) and A1300 (Venturi et al. 2013). The filled points, thered points and the upper limits together provide a view of theGRHS + EGRHS sub-sample in this plane.
Fig. 4.
Left
Radio emission from the spiral galaxy NGC 1633 (DSS R band in colour) detected at 610 MHz (black contours) and 235MHz (magenta contours). Contour levels at 610 MHz are -0.2, 0.2, 0.3, 0.45 mJy beam − . Right
A possible ‘double-double’ radiogalaxy with the outer lobes (labeled east and west lobe) and the inner lobes shown in the inset. The 610 MHz contours (positivemagenta and red negative contours) and 235 MHz contours (positive blue and cyan negative contours) are overlayed on UKIRTinfra-red image shown in colour. Contour levels at 610 MHz are -0.18, 0.18, 0.24, 0.36, 0.48, 0.72, 1.44 mJy beam − and at 235MHz are -1.5, 1.5, 2.0, 2.5, 3.0, 6.0, 12.0 mJy beam − . The black contours in the inset are of the high resolution 610 MHz imagethat resolves the core into lobes with contour levels at -0.15, 0.15, 0.3, 0.4, 0.6, 0.8, 1.0 mJy beam − . Fig. 5.
Left
The complex blend of radio galaxies is toward the right and the di ff use emission is toward left shown in contours at610 and 235 MHz on the DSS R band image in colour. Contours at 610 MHz are 0 . × ( ± , . , , , , , ... ) mJy beam − . Thepositive contours are in blue and negative in grey. The magenta contour levels at 235 MHz are 3 . , . , . , . − .There are no negative contours at 235 MHz in this region. The synthesized beams are 7 . ′′ × . ′′ , PA − . ◦ at 610 MHz and29 . ′′ × . ′′ , PA 35 . ◦ at 235 MHz. Right
The complex blend of radio galaxies in the high resolution 610 MHz image. Thesynthesized beam is 4 . ′′ × . ′′ , PA -80.0. The contour levels are 0 . × ( ± , , , , ... ) mJy beam − . The position of the galaxycluster WHL J083744.3 + × ’.From the known radio halos, there are indications thatthe more powerful radio halos tend to also be the most ex-tended in linear size (Cassano et al. 2007; Murgia et al. 2009;Giovannini et al. 2009). Of course the morphologies of radio ha-los are complex in most cases and the measure of the extent ofradio halo is not robust. We obtained radio halo size as expectedfrom the relation between the halo radius and the expected ra-dio power in order to carry out injections. These expected sizesdi ff ered from the size of 1 Mpc by 2 −
22% with only 3 clustersshowing di ff erences > + + Radio mini-halos are di ff use radio sources found in a fractionof cool-core clusters, surrounding the central galaxy. We ex-tracted cool core clusters from the GRHS and EGRHS sam- ples. The cool core clusters were identified using conditionsbased on central entropy ( K <
50 keV cm ), cooling time( t cool < L core / L > . + + + + ffi cult to detect than possible mini-halos. Themodel profile was injected in the 610 MHz uv- data of eachof the five clusters and upper limits were obtained (Table3). The cluster A2667 was excluded due to the presence ofa radio galaxy near its center. The newly obtained upperlimits and the known mini-halos, namely, RXCJ1504.1-0248(Giacintucci et al. 2011), A1835 (Govoni et al. 2009) , Z7160(V08), RXJ1532.9 + P . - L X plane (Fig. 7, left). The mini-halos inA2626 (Gitti et al. 2004), A2142 (Giovannini & Feretti 2000)and MRC0116 +
111 (Bagchi et al. 2009) listed in literature (e.g.Feretti et al. 2012) are not included in the plot.
6. Discussion
This paper presents the EGRHS sample and the results from theanalysis of radio data on 12 clusters. Sensitive radio images ofthe cluster fields at 610 / /
325 MHz were obtained (Fig. 1 andAppendix 1). Cluster scale di ff use emission such as radio halo,relic or mini-halo are not detected in 11 of these clusters. Weused the method of radio halo model profile injection to estimateupper limits on the detections of radio halos in these clusters.This method was also applied to estimate upper limits on thedetections of mini-halos in a sub-sample of cool-core clustersextracted from the GRHS and the EGRHS samples.The mini-halo in the cluster RXJ1532.9 + ff use emission associated with individual galaxies in twoof the cluster fields. Synchrotron emission from a disk galaxy Ratio of core X-ray luminosity to the luminosity within R (Cassano et al. in prep.). A2626: nature of di ff use emission is uncertain (S. Giacintucciprivate communication); A2142: there is evidence for Mpc-scaleradio halo (Rossetti et al. 2013, Farnsworth et al. submitted);MRC0116 + Fig. 6.
The new upper limits (magenta and blue arrows) areshown in the P . - L X plane with the correlation line (blacksolid line) for giant radio halos reproduced from Brunetti et al.(2009). The magenta arrows are EGRHS clusters, the blue ar-rows are GRHS clusters presented here (see Table 1). The giantradio halos that are hosted in the clusters in the EGRHS + GRHSsample are denoted by filled black circles and red asterisks(USSRHs). The other giant radio halos (black open circles) andupper limits (black arrows) are reproduced from Brunetti et al.(2009).and a radio galaxy with faint lobes were detected in the image ofRXJ0439.0 + ff use emission were detected.We discuss the implications of these results to the under-standing of the radio halos, relics and mini-halos in galaxy clus-ters. The major goal of the GRHS + EGRHS surveys is to estimatethe occurrence of di ff use radio emission in galaxy clusters. Werevise the statistics presented in V08 based on the informationon 35 galaxy clusters available then. Out of the full sample of67 clusters (GRHS + EGRHS), we now have information (pres-ence of radio halo or upper limit) on 48 clusters based on theanalysis of our GMRT data, archival (VLA or GMRT) dataand the literature information. Among these 48 clusters, 11 arehost to giant radio halos . The fraction of radio halos is thus, f RH = / = ± . Following V08 and Brunetti et al.(2009), we divided the sample in two X-ray luminosity bins, A2744 (Govoni et al. 2001), A209 (V07), A521 (Brunetti et al.2008), A1300 (Reid et al. 1999), A2163 (Herbig & Birkinshaw1994; Feretti et al. 2001), RXCJ2003 . − . − Error is estimated assuming Poisson statistics. 9ale et al.: The Extended GMRT Radio Halo Survey I namely, low luminosity bin, 5 × erg s − < L X < × ergs − and high luminosity bin, L X > × erg s − (see Fig. 6,vertical dashed line). 29 clusters out of the total 48 belong tothe high luminosity bin. Of the 11 radio halos, 9 are hosted inthe high luminosity clusters. Thus, the fraction of radio halos inhigh luminosity clusters is f RH = / = ± ± f RH = / = ± + EGRHS samples that are selected based on X-rayluminosity. However, the X-ray lumonisity depends on factorssuch as the dynamical properties of the cluster and the clustermass. We point out that the derived occurrence of radio halosmay change when the occurrence with respect to the cluster tem-perature and / or mass is considered (e.g. Cassano et al. in prep.).We attempt to estimate the mini-halo fraction in the extractedsub-sample of cool-core clusters. A total of 5 mini-halos are de-tected so far in the GRHS + EGRHS samples and 5 upper limitsare obtained. The fraction of mini-halos is ∼
50% in cool-coreclusters, indicating their common occurrence in cool-cores.
The lack of the detections of radio halo / relics in the 11 clustersunderlines the rarity of these sources. The clusters with knownradio halos and relics provide strong evidence that dynamicaldisturbances in the clusters play an important role in the gen-eration of radio halos and relics. Based on the GRHS sampleit has been found that radio halos occur in clusters that showhigher levels of disturbance than the clusters without radio ha-los (Cassano et al. 2010). We searched the literature and carriedout a visual examination of the X-ray images of these clustersto find out about their dynamical states. The visual examina-tion of the X-ray images shows that most of these clusters haveno major signatures of disturbances (Fig. 1). Circularly sym-metric or elliptical morphologies with strong or weak centralpeak are seen in the X-ray images of A689, RXJ0439.0 + + + + L X < erg s − ). Theseproperties are similar to those of other merging systems with lowX-ray luminosities that have been found to be radio-quiet (with-out radio halos / relics) (Cassano et al. 2010; Russell et al. 2012).The only two clusters in this sub-sample with L X > erg s − ,namely A689 and A2261, qualify to be cool cores based on theirproperties. Quantitative studies of the dynamics in these clusterswill be pursued to understand the non-detections of di ff use radioemission in these clusters.The ICM can also be disturbed by the AGN in the clus-ter centers via feedback mechanism (see McNamara & Nulsen2007, for a review). The central AGN during its cycles of activityproduces jets and lobes that can excavate ‘cavities’ in the ICM(e.g. Clarke et al. 1997; McNamara et al. 2001). From the radioimages, it is seen that 7 clusters (out of the 11), namely, A1576,RXJ0439.0 + + + + + / no central radio sources are not cool core clusters.These observations support the idea that cool cores are morelikely to have a central AGN active in radio (e.g. Sun 2009). Adetailed examination of the X-ray images and the radio sourcesin these clusters are required to obtain further information aboutthe state of their ICM. P . - L X correlation A scaling between the radio power of radio halos and the X-ray luminosities of the clusters is known (Liang et al. 2000;Cassano et al. 2006, 2007). The upper limits obtained in this pa-per for the 10 clusters are factors of 3 to 20 below the expectedradio power based on the correlation (Fig. 6). The bimodality inthe distribution of the clusters in this plane suggests that radiohalos are transient sources connected with merging clusters (e.g.Brunetti et al. 2009; Cassano et al. 2010).The bimodality in the P . - L X plane is an impor-tant constraint for the theoretical models. In the turbulent re-acceleration model, the MHD turbulence generated in the ICMdue to mergers is responsible for the acceleration of particles(e.g. Brunetti et al. 2009). The lifetime of a radio halo de-pends strongly on the level of turbulence in the cluster (e.g.Cassano & Brunetti 2005; Brunetti et al. 2009). Therefore whenthe strength of turbulence falls, the radio halo fades rapidly.The bimodality in the P . − L X plane can be explained asan outcome of this phenomenon. The key predictions and ob-servables have been recently reproduced in a high resolutionMHD simulation of the re-acceleration of cosmic ray electronsby turbulence in cluster mergers (Donnert et al. 2013). In thecase of secondary electron models the presence of cosmic rayprotons is expected in all clusters and no abrupt change in thelevel of injection of relativistic electrons can be expected (e.g.Miniati et al. 2001; Dolag & Enßlin 2000). Bimodality has beenqualitatively accounted for in secondary electron models by as-suming amplification of magnetic fields in merging clusters asopposed to relaxed clusters (Kushnir et al. 2009; Keshet & Loeb2010). However, this is disfavoured by rotation measure studiesof galaxy clusters (Bonafede et al. 2011, and references therein).There are also recent attempts to reconcile bimodality and sec-ondary models based on the assumptions that cosmic ray protonsstream at super-Alfvenic speeds in relaxed systems (Enßlin et al.2011).The occurrence of USSRHs is one of the expectations of theturbulent re-acceleration model (e.g. Cassano et al. 2006). Thethree USSRHs are found to occupy the region between the up-per limits and the correlation in the P . - L X plane (Fig. 6).We note here that the upper limits at 1.4 GHz have been scaledfrom those at 610 MHz, assuming a spectral index of 1.3. If asteeper spectral index such as 1.5 or more is used then the up-per limits will be factors of 1.5 or more deeper. Therefore therelative position of the USSRHs and the upper limits needs tobe interpreted with caution. The dual frequency data opens upa possibility of the detection of USSRHs. With the sensitivi-ties that are achieved at 235 and 610 MHz, we can infer thatradio halos of spectral indices 1.8 or steeper would be detectablewith our 235 MHz observations. Systematic radio surveys suchas the EGRHS are necessary in order to populate the P . − L X plane and provide constraints to the theoretical models. In addi-tion to the surveys, characterisation of the spectra of the radio halos needs to be carried out using sensitive multi-wavelengthobservations (e.g. Venturi et al. 2013).Radio mini halos and their occurrence in galaxy clusters areless explored. Based on the cool-core sub-sample of clustersfrom the GRHS and EGRHS, we find that ∼
50% of cool coreclusters have a mini-halo. A possible scaling between the radiopower of mini-halo and the X-ray luminosity was reported byCassano et al. (2008) based on 6 mini-halos known then. Thecombination of GRHS and the EGRHS o ff ers a larger sampleto study the statistics of mini-halos. We used literature data onmini-halos and the upper limits estimated in this work to exam-ine the scaling between the radio power of mini-halos and theX-ray luminosity of the cluster (Fig. 7, left).The best fit line using only mini-halo detections has a slopeof 1 . ± .
52 (solid line). With the inclusion of upper limits,the best fit has a slope of 2 . ± .
61 (dashed line) . Since the P . − L X correlation is consistent with a slope ∼
1, we testthe reliability of this result by evaluating the presence of a corre-lation in the flux-flux space (Fig. 7, right). We find a clearer cor-relation in the flux-flux plane with a best fit slope of 0 . ± . ff erences in the properties within the popu-lation of mini-halos. Unlike the radio halos, mini-halos show alarge scatter in their average radio emissivities (power per unitvolume) (Murgia et al. 2009) indicating a heterogenous popula-tion. However due to small statistics (only 10 mini-halos), theproperties need to be confirmed by future data.
7. Summary and conclusions
The EGRHS is an extensive radio survey of massive galaxy clus-ters with L X (0 . − . > × erg s − in the redshiftrange 0.2-0.4. It is an extension of the GRHS survey (V07, V08).In this paper we presented the EGRHS sample and first resultsbased on the radio data analysis. The EGRHS sample consistsof 17 galaxy clusters, which combined with the GRHS (V08)makes a sample of 67 galaxy clusters. These clusters are beingsystematically surveyed in radio band in order to study the statis-tical properties of the di ff use radio emission in galaxy clusters.The main results of this paper are summarized below:1. Radio images with rms noise in the range 45 - 80 µ Jy beam − at 610 MHz, 0.25 - 0.40 mJy beam − at 325 MHz and 0.55– 1.8 mJy beam − at 235 MHz were obtained. Single or dualfrequency images of 12 clusters are presented in this paper.2. The 610 MHz image of the newly detected mini-halo in theGRHS cluster RXCJ1532.9 + ff use emission associatedwith the remaining 11 clusters were detected. A small scale( ∼
200 kpc) relic is suspected in the cluster Z348. The X-rayimages of these clusters and the information in the literatureabout the dynamical states were examined. None of these 11clusters show extreme merger signatures combined with highX-ray luminosities.3. The method of injection of model radio halos wasused to obtain firm upper limits on 10 clusters (A1576,RXJ0439.0 + + + This was estimated through the parametric EM algorithm as imple-mented in the ASURV package (Isobe et al. 1986).
A267, Z348, A2261, RXCJ0437.1 + P . – L X planeand are found to be factors ∼ + GRHS sample analysed so far is 23 ± ±
11% in the clusters with high X-rayluminosities ( > × erg s − ) and 11 ±
7% in the clusterswith lower X-ray luminosities (5 − × erg s − ).5. From the GRHS sample and the EGRHS clusters presentedhere, a sub-sample of 7 cool core clusters was identifiedusing the criteria based on central entropy, central coolingtime and luminosity ratio. The method of obtaining upperlimits based on model injection is extended to mini-halos.Upper limits on the detection of mini-halos were obtainedfor 5 cool core clusters (RXCJ1115.8 + + P . – L X formini-halos, including the data from literature, is presented.There is an indication of a correlation which needs to beconfirmed by future data. In the GRHS + EGRHS cool-coresub-sample, the fraction of mini-halos is found to be ∼ ff use lobes of a radio galaxy in the field of the clusterRXJ0439.0 + ff use filament are detected in the field of A689.The results on the remaining clusters in the EGRHS sample andthe statistics of radio halos and mini-halos based on the full sam-ple will be presented in a future work. Acknowledgements.
We thank the sta ff of the GMRT who have made these ob-servations possible. GMRT is run by the National Centre for Radio Astrophysicsof the Tata Institute of Fundamental Research. This research has made use ofthe NASA / IPAC Extragalactic Database (NED) which is operated by the JetPropulsion Laboratory, California Institute of Technology, under contract withthe National Aeronautics and Space Administration. We have made use of theROSAT Data Archive of the Max-Planck-Institut fur extraterrestrische Physik(MPE) at Garching, Germany. This research has made use of data obtained fromthe High Energy Astrophysics Science Archive Research Center (HEASARC),provided by NASA’s Goddard Space Flight Center. SG acknowledges the sup-port of NASA through Einstein Postdoctoral Fellowship PF0-110071 awardedby the Chandra X-ray Center (CXC), which is operated by SAO. This workis partially supported by PRIN-INAF2008 and by FP-7-PEOPLE-2009-IRSESCAFEGroups project grant agreement 247653. GM acknowledges financial sup-port by the “Agence Nationale de la Recherche” through grant ANR-09-JCJC-0001-01.
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Fig. 7.
Left
The P . - L X plane for mini-halos. The black arrows are the upper limits on the detection of mini-halos (see Sec.5.1). The black filled circles are mini-halos detected in the GRHS sample. Red points are other mini-halos from the literature(Feretti et al. 2012). The black, solid straight line is the best fit obtained for a possible scaling between the radio-power and X-rayluminosity using only detected mini-halos. The black curved lines encompass the 95% confidence region (i.e. the region that has95% probability to contain the regression line). The dashed line is a best fit also including the upper limits. Right
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Summary of GMRT observations.
Cluster Freq. Beam rms(MHz) ′′ × ′′ , PA ( ◦ ) mJy beam − Abell 1576 610 8 . × .
7, 53 . . × .
8, 43 . . × . − . . × .
2, 35 . + . × . − . . × . − . + . × .
8, 71 . . × .
2, 60.4 0.75RXJ0142.0 + . × .
1, 88.2 0.05235 27 . × .
5, 54.2 1.3Abell 267 610 6 . × .
4, 70.6 0.07Z348 610 14 . × .
7, -13.7 0.065Abell 2261 610 11 . × .
9, 76.0 0.08235 24 . × . − . + . × .
3, 82.0 0.25RXCJ1212.3-1816 325 29 . × .
7, 10.4 0.40Abell 2485 325 18 . × .
4, 36.2 0.25RXJ1532.9 + . × .
1, 82 0.04
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Table 3.
Radio power upper limits using radio halo (first 11)and mini-halo injections. See Sec. 5 for details.
Cluster z rms a S Log ( P . Name mJy b − mJy W Hz − )Abell 1576 0.302 0.09 6 23.78RXJ0439.0 + + + b + c c c + + d Notes. a Rms noise in images tapered to HPBW ∼ ′′ − ′′ . b Reliableupper limit could not be obtained due to a central bright source in thecluster. c The upper limits are scaled from those at 325 MHz using aspectral index of 1 . d Upper limit was not obtained due to a radiogalaxy near the cluster centre. 13ale et al.: The Extended GMRT Radio Halo Survey I
Table 1.
Extended GMRT RHS Sample (first sector, 17 clusters) and part of the GRHS sample. Columns are: 1. Cluster name; 2.Right Ascension; 3. Declination; 4. Redshift; 5. X-ray luminosity (0.1 – 2 keV) in units 10 erg s − (Ebeling et al. 1998, 2000;B¨ohringer et al. 2004); 6. Notes about the cluster. Radio data on the clusters marked with the symbol ‘ √ ’ are presented in this paper. Name RA J DEC J z L X (0.1–2 keV) Notes10 erg s − A68 00 36 59.4 +
09 08 30 0.254 9.47Z348 01 06 50.3 +
01 03 17 0.254 6.23 √ RXJ0142.0 + +
21 30 39 0.280 6.41 √ A267 01 52 52.2 +
01 02 46 0.230 8.57 √ RXJ0439.0 + +
07 15 36 0.244 8.37 √ RXJ0439.0 + +
05 20 43 0.208 5.30 √ A520 04 54 19.0 +
02 56 49 0.203 8.84 Radio halo A689 08 37 29.7 +
14 59 29 0.279 19.68 √ Z1953 08 50 10.1 +
36 05 09 0.373 23.46Z3146 10 23 39.6 +
04 11 10 0.290 17.26Z5247 12 34 17.3 +
09 46 12 0.229 6.32A1576 12 36 49.1 +
63 11 30 0.302 7.20 √ A1722 13 19 43.0 +
70 06 17 0.327 10.78A1835 14 01 02.0 +
02 51 32 0.252 24.48 Mini-halo A2146 15 56 04.7 +
66 20 24 0.234 5.62 No halo RXJ2129.6 + +
00 05 39 0.235 11.66A2552 23 11 33.1 +
03 38 07 0.301 10.07RXCJ0437.1 + +
00 43 38 0.284 8.99 √ RXCJ1212.3 − √ A2261 17 22 28.3 +
32 09 13 0.224 11.31 √ A2485 22 48 32.9 -16 06 23 0.247 5.10 √ RXJ1532.9 + √ , Mini-halo Notes. Corrected for cosmology; Govoni et al. (2001); Murgia et al. (2009); Russell et al. (2011); Giacintucci et al. 2013, in prep.14ale et al.: The Extended GMRT Radio Halo Survey I , Online Material p 1
Appendix A: Radio images of the cluster fields
The radio images of the clusters up to the virial radius are pre-sented here. Natural weights were used to make these images. ale et al.: The Extended GMRT Radio Halo Survey I , Online Material p 2
Fig. A.1. A1576 : GMRT 610 MHz (left) and 235 MHz (right) images in contours. Positive contours are black and negative are greyin all the images in Appendix A. The contours are at 0 . × ( ± , , , ... ) mJy beam − at 610 MHz and 2 . × ( ± , , , ... ) mJy beam − at 235 MHz. The HPBWs at 610 and 235 MHz are 8 . ′′ × . ′′ , p. a. 53 . ◦ and 24 . ′′ × . ′′ , p. a. 43 . ◦ , respectively. The 1 σ levelsin the 610 and 235 MHz images are 0.08 and 0.55 mJy beam − , respectively. The circle has a radius equal to the virial radius forthis cluster (9 . ′ ). Fig. A.2. A689 : GMRT 610 MHz (left) and 235 MHz (right) images in contours. The contours are at 0 . × ( ± , , , ... ) mJy beam − at 610 MHz and 3 . × ( ± , , , ... ) mJy beam − at 235 MHz. The HPBWs at 610 MHz and 235 MHz are 7 . ′′ × . ′′ , p. a. − . ◦ and29 . ′′ × . ′′ , p. a. 35 . ◦ , respectively. The 1 σ levels in the 610 and 235 MHz images are 0.08 and 0.85 mJy beam − , respectively.The circle has a radius equal to the virial radius for this cluster (13 . ′ ). The red boxes mark the positions of the di ff use filament(left box) and the complex of radio galaxies (right box) discussed in Sec. 4.2.2. ale et al.: The Extended GMRT Radio Halo Survey I , Online Material p 3
Fig. A.3. RXJ0439.0 + : GMRT 610 MHz (left) and 235 MHz (right) images in contours. The contours are at 0 . × ( ± , , , ... )mJy beam − at 610 MHz and 6 . × ( ± , , , ... ) mJy beam − at 235 MHz. The HPBWs at 610 and 235 MHz are 7 . ′′ × . ′′ , p. a. − . ◦ and 16 . ′′ × . ′′ , p. a. − . ◦ , respectively. The 1 σ levels in the 610 and 235 MHz images are 0.05 and 1.8 mJy beam − ,respectively. The circle has a radius equal to the virial radius for this cluster (12 . ′ ). Fig. A.4. RXJ0439.0 + : GMRT 610 MHz (left) and 235 MHz (right) images in contours. The contours are at 0 . × ( ± , , , ... )mJy beam − at 610 MHz and 3 . × ( ± , , , ... ) mJy beam − at 235 MHz. The HPBWs at 610 and 235 MHz are 8 . ′′ × . ′′ , p. a.71 . ◦ and 27 . ′′ × . ′′ , p. a. 60 . ◦ , respectively. The 1 σ levels in the 610 and 235 MHz images are 0.06 and 0.75 mJy beam − ,respectively. The circle has a radius equal to the virial radius for this cluster (12 . ′ ). ale et al.: The Extended GMRT Radio Halo Survey I , Online Material p 4
Fig. A.5. RXJ0142.0 + : GMRT 610 MHz (left) and 235 MHz (right) images in contours. The contours are at 0 . × ( ± , , , ... )mJy beam − at 610 MHz and 4 . × ( ± , , , ... ) mJy beam − at 235 MHz. The HPBWs at 610 and 235 MHz are 9 . ′′ × . ′′ , p.a. 88 . ◦ and 27 . ′′ × . ′′ , p. a. 54 . ◦ , respectively. The 1 σ levels in the 610 and 235 MHz images are 0.05 and 1.3 mJy beam − ,respectively. The circle has a radius equal to the virial radius for this cluster (10 . ′ ). Fig. A.6. A267 : GMRT 610 MHz image in contours. The contours are at 0 . × ( ± , , , ... ) mJy beam − . The HPBW is 6 . ′′ × . ′′ ,p. a. 70 . ◦ . The 1 σ level in the image is 0.07 mJy beam − . The circle has a radius equal to the virial radius for this cluster (12 . ′ ). ale et al.: The Extended GMRT Radio Halo Survey I , Online Material p 5
Fig. A.7. Z348 : GMRT 610 MHz image in contours. The contours are at 0 . × ( ± , , , ... ) mJy beam − . The HPBW is 14 . ′′ × . ′′ ,p. a. − . ◦ . The 1 σ level in the image is 0.065 mJy beam − . The circle has a radius equal to the virial radius for this cluster (10 . ′ ). Fig. A.8. A2261 : GMRT 610 MHz (left) and 235 MHz (right) images in contours. The contours are at 0 . × ( ± , , , ... ) mJybeam − at 610 MHz and 1 . × ( ± , , , ... ) mJy beam − at 235 MHz. The HPBWs at 610 and 235 MHz are 11 . ′′ × . ′′ , p. a. 76 . ◦ and 24 . ′′ × . ′′ , p. a. − . ◦ , respectively. The 1 σ levels at 610 and 235 MHz are 0.08 and 0.45 mJy beam − , respectively. Thecircle has a radius equal to the virial radius for this cluster (13 . ′ ). ale et al.: The Extended GMRT Radio Halo Survey I , Online Material p 6
Fig. A.9. RXCJ0437.1 + : GMRT 325 MHz image in contours. The contours are at 1 . × ( ± , , , ... ) mJy beam − . The HPBWis 18 . ′′ × . ′′ , p. a. 82 . ◦ . The 1 σ level in the image is 0.25 mJy beam − . The circle has a radius equal to the virial radius for thiscluster (10 . ′ ). Fig. A.10. RXCJ1212.3-1816 : GMRT 325 MHz image in contours. The contours are at 2 . × ( ± , , , ... ) mJy beam − . The HPBWis 29 . ′′ × . ′′ , p. a. 10 . ◦ . The 1 σ level in the image is 0.40 mJy beam − . The circle has a radius equal to the virial radius for thiscluster (10 . ′ ). ale et al.: The Extended GMRT Radio Halo Survey I , Online Material p 7
Fig. A.11. A2485 : GMRT 325 MHz image in contours. The contours are at 1 . × ( ± , , , ... ) mJy beam − . The HPBW is 18 . ′′ × . ′′ , p. a. 36 . ◦ . The 1 σ level in the image is 0.25 mJy beam − . The circle has a radius equal to the virial radius for this cluster(10 . ′′