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Astron.Nachr./ANxxx(xxxx)x,xxx–xxx New radio halos and relics in clusters of galaxies G. GIOVANNINI1,2, L. FERETTI1, F. GOVONI1,3, M. MURGIA1,3, and R. PIZZO1,4 1 INAF,IstitutodiRadioastronomia,viaGobetti101,40129Bologna,Italy 6 2 DipartimentodiAstronomia,Universita’diBologna,viaRanzani1,40127Bologna,Italy 0 3 INAF,OsservatorioAstronomicodiCagliari,Loc.PoggiodeiPini,Strada54,09012Capoterra(CA),Italy 0 4 KapteynAstronomicalInstitute,Postbus800,9700AVGroningen,Netherlands 2 n a Received<date>;accepted<date>;publishedonline<date> J 3 1 1 Abstract.Wepresentherenewimagesofrelicsandhalosourcesinrichclusterofgalaxiesandthecorrelationbetweenthe v haloradiosurfacebrightnessversustheclusterbolometricX-rayluminosity. 5 8 2 Keywords:galaxies:clusters:individual(A209,A548b,A1758)–radiocontinuum:galaxies–X–rays:galaxies:clusters 1 0 (cid:13)c0000WILEY-VCHVerlagGmbH&Co.KGaA,Weinheim 6 0 / 1. New radio halosand relics h -13 32 p - The knowledge of magnetic fields in clusters of galaxies is 33 o importanttoconfirmtheexistenceoflarge-scalecosmologi- r t cal magnetic fields and to study their properties. It is there- 34 s a forecrucialtoobtaindetailedobservationsofradiohalosand Xiv: brceoulntiicsostnr,a.siWnintescetportehtsheesenectlehuxestrteeenrndmeewdagsdnoaeuttariccfeofisrectlhdarsnesegtrcivelunesgottehbrssaenordvfagdtaiioslatnrxai--l ATION (J2000) 3356 N ar ies:A209,A548b,andA1758.Fromthediffuseradiosources ECLI 37 intheseclusters,equipartitionmagneticfieldsoftheorderof D 0.5×10−6Gaussarederived1. 38 Abell209.Thisclusteratz=0.206isdominatedbyacen- 39 tralcD galaxylocatednearthepeakoftheclustermassdis- tribution.X-raydataandopticaldensitydistributionshowan 40 irregularmorphologywithsignificantsubstructuressuggest- 41 ing the presence of a cluster merger (Mercurioet al. 2003). 01 32 10 05 00 31 55 50 45 40 RIGHT ASCENSION (J2000) TheVLAradioimageafterthesubtractionofdiscretesources (Figure1)showsagiantdiffuseradiohaloattheclustercen- ter,withamajoraxissizeof∼6’(∼1.2Mpc). Fig.1.VLAradioimage(contours)ofthegianthaloinA209 Abell 548b. The cluster A548, at an average redshift z overimposed to the optical map from the Digital Sky Sur- = 0.04, shows a rather complex structure with at least three vey (gray scale). The HPBW is 40”×60”; contours are: - mainsub-clusters.ThecombinationofX-rayandopticaldata 0.2,0.2,0.3,0.5,0.8 mJy/beam. At the cluster distance, 1’ ∼ indicates that A548 is a cluster in a collapsing phase and 200kpc. thereforenotyetdynamicallyrelaxed.Ferettietal.(2006)re- portthedetectionoftwodiffuserelicradiosourcesinA548b, confirmingtheassociationbetweenrelicsandmergers.These center at projected distances ∼ 430 and 500 kpc, and show sources are located on the same side of the cluster’s X-ray a similar shape, flux density, extent, polarization, and spec- Correspondenceto:[email protected] tral index. Another diffuse source, probably a third relic, is 1 weuseH0=70kmsec−1Mpc−1;Ωm=0.3,andΩΛ=0.7 detectedcloseinprojectiontotheclustercenter(Figure2). 2 CORRELATIONS 50 36 -25 45 RELIC 35 34 N (J2000) 50 ON (J2000) 33 DECLINATIO 55 RELIC? RELIC DECLINATI 32 31 -26 00 30 29 05 05 46 15 00 45 45 30 15 00 44 45 30 13 33 00 32 45 30 RIGHT ASCENSION (J2000) RIGHT ASCENSION (J2000) Fig.2. Overlay of the VLA radio image (contours) Fig.3. VLA radio image (contours) of the extended ra- onto the cluster X-ray image from ROSAT PSPC (gray dio structure in A1758N overimposed to the XMM X- scale). The radio HPBW is 15”×30”. Contours are: ray image (gray scale). The HPBW is 45”; contours are: 0.3,0.5,1,2,4,8,16,32,64mJy/beam.Attheclusterdistance,1’ 0.15,0.3,0.5,0.7,1,2,3,5,7mJy/beam.At the cluster distance, ∼50kpc. 1’∼250kpc Abell 1758.Thiscluster at z = 0.279was studiedin de- tail in the X-ray band by David & Kempner (2004). They showedthatA1758consistsoftwohotX-rayluminousclus- ters:A1758NandA1758S.Thenorthernclusterisinthelater stagesofamergeroftwo7keVclusters,whileA1758Sisin theearlierstagesofamergeroftwo5keVclusters. We have detected a radio halo in A1758N. In Figure 3 weshowasuperpositionofthehalosource(discretesources havebeensubracted)andtheXMMclusterimage.Theradio imageshowsadiffuseemission(centralhalo)permeatingthe A1758Nregionwherethetwosubclustersaremerging,∼0.8 Mpcinsize,andtwobrighterperipheralstructuresontheop- positesidewithrespecttotheclustercenter,whichresemble relicradiosources.Thedetectionofaradiodiffuseemission inA1758NandnotinA1758Sisinagreementwiththehot- ter temperature (7keV) of the N subclusters with respect to Ssubclusters(5keV)andwiththeDavid&Kempnerresult Fig.4.Haloradiobrightnessat1.4GHzversusclusterbolo- thatA1758Nisinalatestageofmerger,whileA1758Sisin metric X-ray luminosity. Upper limits (arrows) are A119, anearlymergerstage. A399, A2111, RXCJ1234.2+0947. Empty circles are small size(<1Mpc)halos. 2. Correlations To understand the origin, evolution, and physicalproperties of radio halos and relics it is important to correlate the ra- Feretti(2005)presentedthecorrelationbetweentheaverage diopropertieswith clusterproperties.Clusterswithhalosor radio surface brightness of the radio halo versus the cluster relics are characterizedby strong dynamicalactivity related X-rayluminosity.InFigure4wepresentthiscorrelationin- tomergingprocesses.Moreoverthemostpowerfulradioha- cluding recent new data. It is interesting to note that upper losandrelicsaredetectedinclusterswiththehighestX-ray limitsareconsistentwiththecorrelationsuggestingthatlow luminosity.However,halosarenotpresentinallmergerclus- X-rayluminosityclustersmighthostfaintradiohaloswhich ters.Totakeintoaccountalsoupperlimitstotheradioemis- couldbedetectedonlybyfuturetelescopesasLOFAR,LWA, sion for those clusters where a radio halo is not detected, andSKA. References References References David,L.P.,Kempner,J.:2004,ApJ613,831 Feretti, L.: 2005, in http://www.aoc.nrao.edu/events/xraydio (astro-ph/0406090) Feretti,L.,etal.:2006,MNRAS,inpress Mercurio,A.,etal.:2003,A&A397,431