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4 X-RAY OBSERVATIONS OFTHE MOSTMASSIVE 0 0 DLS SHEAR-SELECTED GALAXY CLUSTERS 2 n a 1 2 3 4 John P. Hughes, Ian Dell’Antonio, Joseph Hennawi, Vera Margoniner, J 1 5 3 4 SandorMolnar, Dara Norman, David Spergel, J. Anthony Tyson, Gillian 2 6 4 2 Wilson, andDavidWittman 1 2 3 4 RutgersUniversity, BrownUniversity, PrincetonUniversity, BellLabs,LucentTechnolo- 5 6 1 gies, CTIO/NSFAAPF, SIRTFScienceCenter v 3 7 Abstract WereportonpreliminaryresultsofourX-raysurveyofthemostmassiveclusters 4 currentlyidentifiedfromtheDeepLensSurvey(DLS).TheDLSclustersample 1 0 is selected based on weak lensing shear, which makes it possible for the first 4 timetostudy clustersinabaryon-independent way. Inthisarticlewepresent 0 X-raypropertiesofasubsetoftheshear-selectedclustersample. / h p Keywords: darkmatter,gravitationallensing,large-scalestructureofuniverse,X-rays:galax- - ies:clusters o r t 1. Introduction s a Nonbaryonic dark matter is apparently the dominant component of galaxy : v clusters, yet all large samples of clusters to date are selected on the basis of i X emission from the trace baryons they contain: visible light from galaxies or r X-rays from hot intracluster gas. Now, for the first time, we have a direct a survey of mass in the Universe that is unbiased with respect to baryons, the Deep Lens Survey (DLS).The DLSis a deep, wide area, multicolor (BVRz’) imagingsurveybeingcarriedoutattheNOAO4-mtelescopes. Thesurveywas designed to detect large scale structures inthe Universe through weaklensing shear, i.e., distortions to the shapes of distant background galaxies caused by gravitationallensingofmassiveforegroundobjects. TheDLSteamhasalready shownthatshear-selection iseffectiveatfindingnewgalaxyclusters: Wittman et al. (2001) report the discovery of CL J2346+0045, the first galaxy cluster identifiedbyitsgravitational effectratherthanitsradiation. Forthisproject, 12squaredegrees oftheDLSdata(themaximumskyarea available at the time) were processed through the weak lens shear pipeline (Wittmanetal.2003),revealingmassconcentrations overawiderangeofred- shifts. Thesemassclusterswererank-ordered bytheirshearsignalandthetop 2 candidates wereproposed forobservation bytheChandraX-RayObservatory incycle 4. Seventargets wereawarded; anadditional candidate wasavailable throughtheChandraarchive. Oneoftheprinciplegoalsofthefollow-upX-ray observations is to confirm that the DLS shear-selected clusters are associated with true virialized, collapsed structures. The basic X-ray information (luminosity,size,morphology, extentofcentralconcentration, andgastemperature) obtained ontheclusters willallowustoassesstheeffectofshear-selection on theLX–TX relation,theclustertemperaturefunction, andtherelationofthese tocluster mass. ThefullDLSX-rayclustersamplewillalsoallowustoquan- tify thefalse-positive rate of“aligned filaments,” i.e., line-of-sight projections that appear asspurious mass concentrations inweak lensing shear maps (e.g., White,vanWaerbeke, &Mackey2002). 2. X-ray Observations We have confidently detected extended X-ray emission from at least five of the eight DLS clusters in the Chandra cycle 4 sample. Although the other three targets have been observed, our analysis is not yet complete and we do notcommentonthemfurtherhere. Figure 1 shows maps of the projected mass (left panels) and X-ray surface brightness (rightpanels)overthe0.5–2keVbandforseveraloftheDLSmass clusters. In the X-ray images serendipitous point sources have been removed and circles denote the locations of extended X-ray sources detected at signal- to-noise ratios greater than 3. The two highest-ranked shear-selected clusters are strong X-ray sources, with multiple subclusters associated with each sys- tem. ThiscanbeseenclearlyintheX-rayimageofDLScluster2(toppanelof Figure1). Intheopticalimagestherearealargenumberofbrightgalaxiesthat arepresumablyclustermembers,howevernopublishedredshiftsareavailable. The fourth ranked cluster (middle panels) is unusual in having only a single X-raycomponent. Itiscenteredonagalaxyataredshiftofz = 0.19. Thelast ranked cluster in the Chandra cycle 4 sample (bottom panels) shows two sig- nificantextended X-raysources. Thesouthwestern component wasconfirmed by the DLS team as a massive cluster at z = 0.68 (Wittman et al. 2003) and even shows a giant arc from strong lensing. There is no redshift available for thenorthernX-rayconcentration. In Table 1 we present selected numerical results for the five X-ray clusters associated with shear peaks. In each case only values for the X-ray cluster component with the highest flux are given. Redshift information for clusters 2 and 7 is not yet available; we give very preliminary luminosity and mass estimates based onapproximate redshifts from themagnitudes ofthemember galaxies. PhotometricredshiftsforallX-rayclustersareintheprocessofbeing determinedfromourimagingdata. WeusedtheX-rayluminosity-temperature X-rayObservationsofDLSClusters 3 Table1. X-rayPropertiesofDLSMassClusters. FX (0.5–2keV) Lbol M200 Cluster z (ergs−1cm−2) (ergs−1) (1014M⊙) DLSClu1 0.298 6.7×10−13 8.5×1044 5.7 DLSClu2 ∼0.2 2.9×10−13 1.1×1044 1.9 DLSClu4 0.1894 1.4×10−14 4.3×1042 0.4 DLSClu7 ∼0.4 1.9×10−14 3.1×1043 1.0 DLSClu8 0.68 2.4×10−14 1.7×1044 2.4 relation(Arnaud&Evrard1999)toestimateclustertemperatures andthenthe mass-temperaturerelation(Evrard,Metzler,&Navarro1996)todeterminethe mass within a density contrast of δc = 200. These relations are derived from or calibrated against low-redshift clusters; at this point we have not made any adjustments for the redshift range of our sample. Still the mass estimates are consistentwithsimulationsbyourgroupthatshowanexpectedmassrangefor DLSshear-selected clustersextending fromroughly5×1013M to1015M ⊙ ⊙ withapeaknear3×1014M . Anadditional directmeasurement ofthemass ⊙ canbemadefromtheshearmaps;thisworkisinprogress. 3. Conclusions TheDLSisclearlydiscovering truethree-dimensional clusters ofmass,hot X-raygas,andgalaxies. WefindawiderangeofX-rayluminosityforclusters with similar weak lensing shear. Nearly every shear peak contains multiple X-ray clusters, while the high mass clusters we detect are particularly com- plexwithupto4or5individually resolved subcomponents. Workinprogress on this unique galaxy cluster sample includes measuring X-ray temperatures from Chandra and XMM-Newton spectra, deriving redshifts and velocity dis- persionsfromground-based spectroscopy, moredetailedmassdeterminations, andadditional numericalsimulations. Acknowledgments ThisworkwaspartiallysupportedbyChandragrantGO3-4173AandNASA LTSAgrantNAG5-3432toJPH. References Arnaud,M,&Evrard,AE1999,MNRAS,305,631 Evrard,AE,Metzler,CA,&Navarro,JF1996,ApJ,469,494 White,M,vanWaerbeke,L,&MackeyJ2002,ApJ,575,640 Wittman,D.,Tyson,JA,Margoniner,VE,Cohen,JG,&Dell’Antonio,IP2001,ApJ,557,L89 Wittman,D.,Margoniner,VE,Tyson,JA,Cohen,JG,&Dell’Antonio,IP2003,ApJ,submitted 4 DLS Clu 2 Mass DLS Clu 2 Chandra ACIS-I 5 5 MINUTES 0 MINUTES 0 ARC ARC -5 -5 5 0 -5 5 0 -5 ARC MINUTES ARC MINUTES DLS Clu 4 Mass DLS Clu 4 Chandra ACIS-I 5 5 MINUTES 0 MINUTES 0 ARC ARC -5 -5 5 0 -5 5 0 -5 ARC MINUTES ARC MINUTES DLS Clu 8 Mass DLS Clu 8 Chandra ACIS-I 5 5 MINUTES 0 MINUTES 0 ARC ARC -5 -5 5 0 -5 5 0 -5 ARC MINUTES ARC MINUTES Figure 1. Projected mass (left) and X-ray surface brightness (right) of DLS mass clusters no.2(top),4(middle),and8(bottom).