Abundance profiles and cool cores in galaxy groups

0.37 MB·English

by  Ria Johnson

Mon.Not.R.Astron.Soc.000,1–15(2010) Printed19January2011 (MNLATEXstylefilev2.2)
Abundance profiles and cool cores in galaxy groups
1⋆ 2 1 3
Ria Johnson , Alexis Finoguenov , Trevor J. Ponman , Jesper Rasmussen ,
1
Alastair J. R. Sanderson
1SchoolofPhysicsandAstronomy,UniversityofBirmingham,Edgbaston,BirminghamB152TT,UK
2Max-Planck-Institutfu¨rextraterrestrischePhysik,Giessenbachstraße,85748Garching,Germany
1 3DarkCosmologyCentre,NielsBohrInstitute,UniversityofCopenhagen,DK-2100Copenhagen,Denmark
1
0
2
19January2011

n
a
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ABSTRACT

7 Using data from the Two DimensionalXMM-Newton Group Survey(2dXGS), we have ex-
1 amined the abundance profile properties of both cool core (CC) and non cool core (NCC)

galaxygroups.ThetenNCCsystemsinoursamplerepresentapopulationwhichtodatehas
]
O been poorlystudied in the groupregime.Fitting the abundanceprofiles as a linear function
oflog radius,we find steep abundancegradientsin coolcore (CC) systems, with a slope of
C −0.54±0.07.Incontrast,noncoolcore(NCC)groupshaveprofilesconsistentwithuniform
h. metallicity.ManyCCgroupsshowacentralabundancediporplateau,andwefindevidence
p foranticorrelationbetweenthecoreabundancegradientandthe1.4GHzradiopowerofthe
- brightest group galaxy (BGG) in CC systems. This may indicate the effect of AGN-driven
o mixing within the central ∼0.1r500. It is not possible to discern whether such behaviouris
r
t presentintheNCCgroups,duetothesmallanddiversesamplewiththerequisiteradiodata.
s
ThelackofstrongabundancegradientsinNCCgroups,coupledwiththeirlackofcoolcore,
a
[ andevidenceforenhancedsubstructure,leadsustofavourmergingasthemechanismfordis-
ruptingcoolcores,althoughwecannotruleoutdisruptionbya majorAGN outburst.Given
1
the impliedtimescales, the disruptiveeventmusthaveoccurredwithin the past few Gyrsin
v
mostNCCgroups.
7
1 Keywords: galaxies:clusters:general-intergalacticmedium-X-rays:galaxies:clusters
3
3
.
1
0
1 INTRODUCTION abundancegradientinNGC5044wasalsoobservedbyBuoteetal.
1
(2003) using XMM-Newton and Chandra data, and recent stud-
1 The dominant baryonic mass component in galaxy groups and
: ies have shown the presence of an abundance gradient to be a
v clusters is the hot X-ray emitting intracluster medium (ICM),
common feature (e.g. Moritaetal. 2006; Rasmussen&Ponman
i with stellar mass becoming increasingly important as mass
X 2007; Tokoietal. 2008; Komiyamaetal. 2009; Satoetal. 2009).
decreases (Gonzalez,Zaritsky&Zabludoff 2007; Giodinietal.
Rasmussen&Ponman (2009) also find a central excess of
r 2009). Studying the metallicity of the ICM can provide insight
a iron in all but two of their groups, the presence of which can
into the processes that have shaped its thermodynamic history.
be explained solely by supernovae Type-Ia products from the
TheheavyelementsobservedintheICMoriginatepredominantly
central galaxy. The excess extends beyond the optical limits
from supernovae explosions, which eject material into the ICM
of the central galaxy, as also seen in clusters (David&Nulsen
(Arnaudetal.1992).Gascanalsoberemovedfromgalaxies,thus
2008; Raseraetal. 2008). The re-distribution of enriched gas
enriching the ICM with metals, through processes such as ram-
can be achieved by outflows from active galactic nuclei (AGN)
pressurestripping(Gunn&Gott1972)andgalaxy-galaxyinterac-
(e.g. Mathews,Brighenti,&Buote 2004; Rebuscoetal. 2006;
tions (see Schindler&Diaferio 2008, for a review of enrichment
Molletal. 2007), the presence of which iscommonly invoked to
processes).Theefficiencyofanyonetransportprocessdependson
explain the lack of catastrophic cooling in the centres of groups
thepropertiesofboththegalaxiesandtheirlarge-scaleenvironment
andclusters.
(Schindler&Diaferio2008,andreferencestherein).
Using ASCA and ROSAT observations, The division of galaxy clusters into samples of cool core
Finoguenov&Ponman (1999) found the groups HCG62 and (CC) and non cool core (NCC) systems is well-established
NGC5044 to have significant negative abundance gradients, (e.g. Peresetal. 1998). Recent work has shown both CC and
a result also seen in the ROSAT sample of Buote (2000). The NCC galaxy clusters to show similar, steep abundance gradients
(Sanderson,O’Sullivan,&Ponman2009;Sivanandametal.2009).
However, earlier observational work by DeGrandi&Molendi
⋆ Contactvia:[email protected] (2001) indicated that NCC clusters have flat abundance profiles,
(cid:13)c 2010RAS
2 R. Johnson,A. Finoguenov,T.J.Ponman,J. Rasmussen& A.J. R. Sanderson
in comparison tothe steep abundance gradients seen in CC clus- metallicity (Buote&Fabian 1998). To check for this, a second
ters.TheprevalenceofmergingsystemsintheNCCsampleofthis spectral analysis is performed, in which spectra are fitted with a
work led the authors to interpret mergers asa mechanism for re- two–temperature(2T)model,inwhichabundanceistakentobethe
distributingmetals. sameinbothphases.Tobetterconstrainthese2Tmodels,spectra
ThedivisionintoCCandNCCclasseshasonlyrecentlybeen wereextractedacrossawiderenergyrange(0.5–7 keV).Theorig-
applied to study the properties of a sizeable sample of systems inalmotivationforusingasmallerenergyrangefor1Tfitswasto
inthegroupregime(Johnson,Ponman,&Finoguenov2009).The constrainthetemperatureprimarilyusingthepositionofthelines,
originofNCCclustersremainsanopenquestion,giventheirshort aiming to reduce bias in the metallicity arising from any distor-
centralcoolingtimes(Sanderson,Ponman&O’Sullivan2006),in- tioninthecontinuum.Weconcentratehereonthepropertiesofthe
dicating that either the formation of cool cores in these sys- abundance profiles of groups, having already explored the diver-
tems has been suppressed, for example through pre-heating (e.g. sityin group properties such as entropy, and the implications for
McCarthyetal.2008)orthermalconduction(e.g.Voigt&Fabian feedbackprocesses,inJohnsonetal.(2009).
2004),orthecoresinNCCsystemshavebeendisruptedbymerg- We are entering an era where large galaxy samples
ers (e.g. Allenetal. 2001) or AGN heating (see the review by can be used to study the gas properties of galaxy groups
McNamara&Nulsen2007).Thesephysicalprocessesscalediffer- (e.g. Rasmussen&Ponman 2007; Sunetal. 2009). In particular,
entlywithsystemmass,sowecangainsignificantinsightintothe Rasmussen&Ponman (2007, hereafter referred to as RP07) de-
originofNCCsystemsby studyingNCCgroups. Theabundance riveddetailedtemperatureandabundanceprofilesfor15systems,
behaviourinNCCgroupshasnotpreviouslybeenstudiedinasam- 14 of which were shown to host a CC. The size and diversity of
pleofanysize,andcouldproveausefuldiagnosticinestablishing our sample allows its division into CC and NCC systems (e.g.
thedominantphysicalprocessesinfluencingtheICM. Peresetal. 1998), based on the properties of their observed tem-
The layout of the paper is as follows. In Section 2 we de- peratureprofiles.ThegroupsinoursamplewereclassifiedasCCs
scribethegroupsampleanddataanalysis,inSection3wepresent if the ratio of the temperature in the radial range 0.1–0.3r500 to
the mean temperature profile of the CC and NCC groups and in the temperature in the radial range 0.0–0.05r500 was found to
Section 4we present the abundance profiles of theCC and NCC be greater than 1. This was found to be a successful discrimina-
groups. We discuss our results in Section 5 and present our con- tor between the systems showing central temperature drops and
clusions in Section 6. Solar abundances are quoted as those of thosewhichdonot.Althoughnotastatisticallyselectedsample,the
Anders&Grevesse(1989). 18CCand10NCCgroupsallowustoidentifytrendsinproperties
basedonthissegregation–afirstinthestudyofgalaxygroups.
Tonegatetheeffectsofthedifferingsizesofthesystemsunder
consideration,wehavescaledradialmeasurementsbyr500 (mea-
2 GROUPSAMPLEANDSPECTRALANALYSIS
suredinkpc),theradiuswithinwhichthemeandensityisequalto
Oursampleof28galaxygroupsisacombinationofthegroupswith 500timesthecriticalvalue.Thiswasdefinedforthe2dXGSgroups
thehighestqualityXMM-NewtondatafromtheTwo-Dimensional byFinoguenovetal.(2006,2007)inthefollowingway,
X(2M00M6-,N2e0w07to)naGndrotuhpeSgruoruvpeysa(2mdpXleGoSf)MsaamhpdlaevoifeFtainl.o(g2u0e0n5o)v.eHtearle. r500 =0.391T¯0.63h−701, (1)
wepresent asummaryofthesampleandthedataanalysisproce- whereT¯ isthetemperature(inkeV)measuredintheradialrange
dures,althoughwereferthereadertoJohnsonetal.(2009)forade- 0.1–0.3r500usingasingle–tempeaturespectralmodel.Thegroups
taileddiscussionofthegroupsample.Twenty-sevenofthegroups includedinourworkfromtheMahdavietal.(2005)samplehave
are situated within z < 0.024, with the final group at a redshift beenre-analysedtoextractT¯andr500.
of0.037(RGH80,seeMahdavietal.2005).Thedatareductionis
describedindetailbyMahdavietal.(2005)andFinoguenovetal.
2.1 BackgroundFittingMethodology
(2006, 2007), but we present a brief summary of the approach
here.Insteadofatraditionalannularspectralanalysis,spectrawere OurapproachtothecomplexissueofremovingtheXMM-Newton
extractedfrom regionsof contiguous surface brightness and tem- backgroundusesafittingmethodologythatallowsforthefactthat
perature. This deprojection method involves no a priori assump- thebackground ischanging intimeand space. Thedetails of the
tion of spherical symmetry, but on the other hand it does not background treatment adopted in obtaining the XMM-Newton re-
correct for emission from overlying layers of material. We re- sultsusedinthisworkarepresentedbyFinoguenovetal.(2007).
ferreaderstoMahdavietal.(2005),Finoguenovetal.(2006)and Weperformthestandardsubtractionofthequiescentbackground
Finoguenovetal.(2007)forfulldetails. andallowforasoftcomponent(T 0.2keV)toaccountforvaria-
∼
Resultsfromtwospectralanalysesarepresentedhere.Inthe tionsintheGalacticforeground.Inordertofullydescribethenon–
first,spectrawereextractedintherange0.5–3 keVandfittedwith X-raybackground,uptotwopower-lawswerefittedinadditionto
single–temperature (1T) hot plasma (APEC) models to yield the thethermalmodel.Thesepower-lawswerenotconvolvedwiththe
temperatureT andabundanceZineachregion.Deprojectedvalues effective area of the telescope, achieved using the ‘/background’
ofentropySandpressureP werecalculatedbyassumingalength modelinXSPEC.IntheX-rayfaintestregionsofgroupsthisback-
alongtheline-of-sightforeachspectralregionderivedfromitsdis- ground component dominates at energies E & 3 keV. In combi-
tancetothecentreofthesystem.Theseresultshavealreadybeen nationwiththedistinctcontinuumshapeofthe 1keVthermal
∼
usedtoexaminethefeedbackpropertiesofgroups(Johnsonetal. groupemission,thisallowsustocharacterisethiscomponentina
2009). robustandunbiasedmanner.
Assuming a single temperature model in regions where a Whencomputinguncertaintiesonfittedsourceparameters,all
spreadoftemperaturesispresent,asmaybethecasewithincool other parameters, including those associated withthefittedback-
cores or where regions of different temperature are projected on groundmodel,wereallowedtoreoptimise.Hence,uncertaintieson
topof one another, can lead tosystematicunderestimation of the derivedT andZ duetothebackground level areincludedinour
(cid:13)c 2010RAS,MNRAS000,1–15
Abundanceprofilesof groups 3
errorbudgets.Thisisamoreflexibletreatmentofthebackground
comparedtothatoftenemployedfornearbygalaxyclusters,where
the background is inferred using different observations. In fitting
cluster emission, a recent practice has been to add a systematic
error due to the background subtraction. We have refrained from
doing so, since we directly fit for local background shape in the
spectral analysis. However, the faintest groups studied here (and
those having short XMM-Newton exposures) cannot be traced to
theedgeoftheXMM-Newtonfield-of-view,andthereforeitisnot
possibletoaccuratelyfitthesourcespectrumandpower-lawcom-
ponent in these outer regions. Such zones are therefore excluded
fromouranalysis.
Toshowthevariationindataqualityintheoutermostregions
usedforabundancedeterminations,weplotinFigure1examplesof
thefittedspectraandbackgroundfortwoofthegroupsinoursam-
ple(NGC507andNGC5171).Thesewereconsideredtoshowtyp-
ical‘best’and‘worst’cases,intermsofconstrainingboththeline
and continuum emission in the spectra. The Figure demonstrates
that even in the worst case (NGC5171), the line and continuum
emissionarewell-constrained,andshow thatthesourceemission
isclearlydiscerniblefromthebackground, indicatingthatweare
notover-interpretingthedataatlargeradius.Tofurthertestthero-
bustness of our spectral results and guard against the possibility
thattheχ2–minimisationofourfitswouldbecometrappedinlocal
ratherthanglobalminima,wealsoinspectedtheχ2contourmaps
intheT–Zplaneforanumberofgroupsandspectralregions.Inall
casesconsidered,onlyonemiminumwasseen,evenforconfidence
rangeslargerthan3σ.
3 TEMPERATUREPROFILES
Figure1.X-rayspectra(datapoints)andfittedsource+backgroundmod-
To illustratethe key differences between the temperature profiles
els(solidline)forthegroupsNGC507(top)andNGC5171(bottom).The
of CC and NCC groups, we have stacked and scaled radially to
dashedlineshowstheremainingbackgroundcomponentoncethestandard
r500 thetemperatureprofilesderivedfromthe1Tspectralfitsfor backgroundsubtraction hasbeenappliedusingblankskyfields.Forboth
eachsub-sampletogivetypicalprofiles.Wehaveremovedthede- groups,thesespectrawereextractedfromtheoutermostregionsforwhich
pendence on the size of the system by dividing the temperature abundancedeterminationswerepossible.
profilesbythecharacteristicmeantemperature(derivedwithinthe
radialrange0.1–0.3r500).Weperformedalocalregression‘loess’
fittotheCCtemperatureprofiles,weightingthesefitsbytheinverse larger measurement errors in this region of lower surface bright-
varianceofthetemperaturemeasurementateachpoint.Thealgo- ness.Figure2indicatesahigherdegreeofconsistencybetweenthe
rithm fits a two-degree polynomial function using weighted least temperatureprofilesofCCsystems,shownviathenarrowstandard
squaresintheinthelocalneighbourhood ofeachdatapoint.The errorincomparisontotheNCCsystems.
sizeoftheneighbourhoodisdefinedtoincludeaspecifiedpropor-
tionofthedata,whichthendictatesthesmoothnessoftheresult-
ingfit.Thedistancetoeachneighbour isusedtoweightthefitat
4 ABUNDANCEPROFILES
eachpoint.Formoreinformation,wereferthereadertoCleveland
(1979)andCleveland,Grosse&Shyu(1992). Finoguenov&Ponman (1999) and Buote (2000) showed CC
However,duetothediversityinthetemperatureprofileprop- galaxy groups to have a central iron peak, a result confirmed for
ertiesoftheNCCgroups,theregressionfitinthiscasewasunsuc- alargersampleofgroupsbyRP07.However,theabundancepro-
cessful,andinsteadwedividedthedataintofourradialbins,each filesofNCCgroupshavenotbeenpreviouslyinvestigated.Figures
containingbetween24and25datapoints.Tomakeadirectcom- 3 and 4 show the abundance profiles from both 1T and 2T spec-
parisonwiththeCCprofile,wecalculatedaweightedmeanofthe tral fits,for both the CC and NCC groups inthe2dXGS sample.
scaledtemperaturepointsineachradialbin,andalsocalculatedthe Inbothfigures,thehorizontal errorbarsshow theradialwidthof
standarderroronthemeanscaledtemperature(i.e.thermsscatter each bin, and the vertical error bars show the measurement error
of the n values falling in each bin, divided by √n), to show the derivedfrom XSPEC,whichtakesintoaccount theuncertainty on
typicalbehaviouroftheNCCtemperatureprofiles.Thesetemper- themodelledbackground.
atureprofilesfortheCCandNCCgroupsareshowninFigure2. Asexpected,the2Tmodelsgivehighermetallicity,especially
ThestandarderrorontheregressionfittotheCCgroupsinflatesat inregionsfromthewhichthespectrumisnotwell-representedby
bothsmallandlargeradius;thisissimplyduetothelowernumber anisothermalplasma.Thisisespeciallythecasewithincoolcores,
of data points in these regions. The larger standard error at radii wherethesteepgradientresultsinregionsofdifferingtemperature
greater than 0.5r500 reflects the increased variance arising from beingprojectedontopofoneanother,andalsothermalinstability
(cid:13)c 2010RAS,MNRAS000,1–15
4 R. Johnson,A. Finoguenov,T.J.Ponman,J. Rasmussen& A.J. R. Sanderson
1.4 1.2
1
3 1.
1.
0
2 1.
1. 9
0.
1
1. 8
0.
(keV)mean0.91.0 ()danceZsolar0.60.7
T/T0.8 Abun0.5
4
7 0.
0.
3
6 0.
0. 2
0.
5
0. 1
0.
4
0. 0.0
0.01 0.05 0.1 0.5 1
0.01 0.05 0.1 0.5 1
r/r500 r r500
Figure2.Thetypicaltemperatureprofilesfrom1Tspectralfits(scaledby Figure5.Thestackedabundance profiles ofthegroups,dividedintothe
the mean group temperature, measured in the radial range 0.1–0.3r500) CC(opencircles)andNCC(filledsquares)sub-samples.Theresultsofthe
forCCgroups(blackconfidenceregionandwhitedottedline)andforNCC 1Tfitsareshowningrey,andtheresultsofthe2Tfitsareshowninblack.
groups(filledsquareswitherrorbars).Thetypicaltemperatureprofileinthe Theverticalerrorbarsarethestandarderroronthemeanprofile,andthe
CCcaseisderivedviaaweightedlocalregressionfit,wheretheassociated horizontal error bars show the radial width of each bin. Thedashed and
confidenceregionshowsthestandarderroronthefit.Thenumberofgroups solidlinesarelinearfitstothewholedatasetofabundancesfromtheCC
contributingtotheCCprofilefallstotwoataradiusof0.6r500,sothein- andNCCgroupsrespectively,colourcodedforthe1T(grey)and2T(black)
terpretationoftheprofilebeyondthisradiusshouldbetreatedwithcaution. fits.
DuetopoorerstatisticsintheNCCcase,wehavestackedtheprofilesinto
fourradialbins,calculatingthemeanscaledtemperature(greysquares)and
r
thestandarderroronthemeanscaledtemperature(greyerrorbars). ZCC =−0.42(±0.04)log(cid:16)r500(cid:17)+0.03(±0.04)Z⊙, (2)
andfortheNCCgroups,
mayresultinmultiphasegas(Buote&Fabian1998).Wenotethat r
theresultsfrom1Tand2Tmodelsconvergeatlargeradii,andthe ZNCC =−0.04(±0.05)log(cid:16)r500(cid:17)+0.17(±0.05)Z⊙. (3)
abundanceoffsetbetweenthetwomodelsismoresignificantinthe
Underthe2Tspectralmodels,thefittedtrendfortheCCgroupsis,
caseofCCgroups,wheretheinferredabundancegradientissteep-
eanneedspbeycitahlelyussetriokfinag2eTxammopdleel..NGC5044(seeFigure3)provides ZCC =−0.54(±0.07)log(cid:16)r5r00(cid:17)+0.12(±0.07)Z⊙, (4)
AbundanceprofilesinCCandNCCgroupscanbecompared andfortheNCCgroups,
bystackingresultsfromthegroupsineachsubsample.Wedivided
r
tehqeuaralldyiaslpraacnegdeboinfsth(eindlaotagfsopracthee),CaCndawndithNinCCeascyhstreamdisalinbtionfidvee- ZNCC =−0.10(±0.10)log(cid:16)r500(cid:17)+0.22(±0.09)Z⊙. (5)
terminedthemeanabundancefromtheensembleofresultsfalling Clearly, the CC systems exhibit a much steeper abundance
withinthisbin,andastandarderrorfromtheirscatter.Theresultis gradient, compared totheNCC systems.ThefittotheNCCpro-
showninFigure5.Resultswerederivedseparatelyfor1Tand2T filesisconsistentwithbeingflatwithinthequotedstandarderrors.
fits,toillustratetheimpact ofthe2ndtemperaturecomponent on Thisistrueforboththefitsfromthe1Tmodelsandthe2Tmodels.
thefittedabundances. Thehorizontal error barsinFigure5show Inthe case of the CC profiles, results from2T fitsgive a steeper
thewidthoftheradialbinsusedinthestackinganalysis.Thever- slopethan1Tmodels.
ticalerrorbarsshowthestandarderrorforeachradialbin.Thisis ThegroupHCG51hasarelativelyhighabundanceinthe1T
largerfor2Tmodels,sincethelargernumberoffreeparametersin fits( 0.5–0.8Z⊙)atradiibetween0.3r500and0.5r500,whichaf-
∼
themodelleadstogreaterscatterintheresults. fectsthecalculationofthemeanabundanceintheoutermostbinof
Figure5alsoshowstheresultsofperformingalinearregres- theNCCprofileinthiscase.ToassesstheimpactofHCG51onthis
sion on the original unbinned data for the CC and NCC samples meanprofile,were-calculatedthemeanabundanceintheouterbin,
separately.Nostatisticalweightinghasbeenappliedwhencalculat- excludingHCG51.Thisreducedthemeanvalueto0.14 0.02Z⊙
±
ingtheseregressionlines,sincethevarianceaboutthemeanprofile from0.24 0.06Z⊙.Otherbinsareonlymarginallyaffectedbythe
±
isdominatedbysystem-to-systemvariations,ratherthanstatistical exclusion of HCG51. Fitting a straight line model in log–linear
scatter.Wefitlinearmodelsinlog–linearspaceusingtheRfunction spacetotheNCCgroups,excludingallHCG51data,wefind
‘LM’forlinearregression,findingthefollowingrelations,using1T r
models,fortheCCgroups, ZNCC =−0.09(±0.04)log(cid:16)r500(cid:17)+0.10(±0.04)Z⊙, (6)
(cid:13)c 2010RAS,MNRAS000,1–15
Abundanceprofilesof groups 5
2−T 1−T
−2.0 −1.0 0.0
NGC5846 HCG42 NGC2300
2.5
2.0
1.5
1.0
0.5
0.0
NGC4636 SS2B153 NGC5129
2.5
2.0
1.5
1.0
0.5
0.0
NGC4325 HCG62 NGC4261
2.5
2.0
)
ar 1.5
sol 1.0
Z 0.5
(
0.0
e
c RGH80 HCG97 NGC5044
n
a
d 2.5
n 2.0
u
1.5
b
A 1.0
0.5
0.0
NGC533 NGC2563 NGC507
2.5
2.0
1.5
1.0
0.5
0.0
SRGB119 NRGB184 NGC4073
2.5
2.0
1.5
1.0
0.5
0.0
−2.0 −1.0 0.0 −2.0 −1.0 0.0
log (r/r )
10 500
Figure3.TheabundanceprofilesoftheCCgroupsinthe2dXGSgroupsample,showninlog–logspace.Thecoloursdenote1T(red)and2T(blue)spectral
fits.Verticalerrorbarsaremeasurementerrorsandhorizontalerrorbarsshowthewidthofeachradialbin.TheverticaldottedlinesshowtheXMM-Newton
field-of-viewof16′forallgroupsexceptNGC4636andNGC5044,wheretheoffsetofthepointingsshiftstheouterboundariesto18′and17.7′respectively.
ThesolidlinesshowtheresultsoflinearmodelfitstoallCCgroups,forboththe1T(red)and2T(blue)spectralfits.
(cid:13)c 2010RAS,MNRAS000,1–15
6 R. Johnson,A. Finoguenov,T.J.Ponman,J. Rasmussen& A.J. R. Sanderson
2−T 1−T
−2.0 −1.5 −1.0 −0.5 0.0
IC1459 HCG15
1.5
1.0
0.5
0.0
HCG68 NGC4168
1.5
1.0
0.5
0.0
) PAVO HCG92
ar
ol
s
Z 1.5
(

e
c 1.0
n
a 0.5
d
n
u 0.0
b
A A194 HCG51
1.5
1.0
0.5
0.0
NGC5171 3C449
1.5
1.0
0.5
0.0
−2.0 −1.5 −1.0 −0.5 0.0
log (r/r )
10 500
Figure4.TheabundanceprofilesoftheNCCgroupsinthe2dXGSgroupsample,showninlog–logspace.Thecoloursdenote1T(red)and2T(blue)spectral
fits.Verticalerrorbarsaremeasurementerrorsandhorizontalerrorbarsshowthewidthofeachradialbin.TheverticaldottedlinesshowtheXMM-Newton
field-of-viewof16′forallgroups.ThesolidlinesshowtheresultsoflinearmodelfitstoallNCCgroups,forboththe1T(red)and2T(blue)spectralfits.
(cid:13)c 2010RAS,MNRAS000,1–15
Abundanceprofilesof groups 7
yieldingaslopethatisnon-zero(withina95%confidenceinterval),
Table1.Thefittedintercepts,slopesanderrorsformodelsfittedtothe1T
butstillmuchshallowerthanthatfoundintheCCsystems.Inthe and2Tresultswith3C449andHCG51reclassifiedasCCsystems.
caseof2Tspectralfits,excludingHCG51givesameanprofilefor
NCC CC
NCCgroups
1-T Slope -0.05±0.05 -0.06±0.12
r Intercept 0.13±0.05 0.03±0.03
ZNCC =−0.10(±0.11)log(cid:16)r500(cid:17)+0.21(±0.10)Z⊙, (7) 2-T Slope -0.06±0.12 -0.56±0.06
Intercept 0.24±0.12 0.09±0.07
withaslopewhichisconsistentwithzerowithinthe1σerror.
The presence of acentral abundance peak isconsistent with
being built from the products of type Ia supernovae occurring in oftheCCsystemsintheChandrasampleofRP07showstemper-
the central galaxy, in both groups (Rasmussen&Ponman 2009) aturedropsonsuchsmallradialscales.Most importantlyforthis
andclusters(David&Nulsen2008).However, thetypicaloptical work is the observation by Sunetal. (2009) of compact cool re-
extentofthecentralgroupgalaxyisonly0.05r500,indicatingthat gionswithin10 kpcin3C449andHCG51,classifiedinthiswork
themetallicityprofileoftheCCandNCCsystemscontinuestofall asNCCsystems.Wetestedthesusceptibilityofourresultstothe
welloutsidethecentralgalaxy.Thissuggeststhatmetalshavebeen appliedCC/NCCdefinitioninthesetwosystemsbychangingtheir
expelled fromthecentral galaxy intothesurrounding intracluster designationanddeterminingtheabundancegradientsoftheresult-
medium.Weestimateameangasmassweightedmetalfractionfor ingstackedCCandNCCprofiles.Againfittingalinearmodelin
theCCandNCCgroupsbysummingtheproductofthemetallicity log–linearspacetotheresultsfromboththe2Tmodelsandthe1T
andgasmassoveraseriesofradialshells,anddividingbythetotal models,wefindtheslopeandinterceptof theabundance profiles
gasmasscontainedwithintheseshells.Thegasmasswasderived tobeconsistent withtheoriginalprofileswithinthestatederrors,
from β–model fits to the gas density profiles (see Johnsonetal. forboththeCCsandtheNCCs.Thefittedinterceptsandslopesare
2009,formoreinformation).Thecalculationofthemetalfraction showninTable1.Therefore,evenif3C449andHCG51havetheir
waslimitedtowithin0.3r500 toensureconsistentradialcoverage CCstatusreclassified,theresultsfromthestackinganalysisarenot
betweenthegroups, andthisisalsotheradiuswheretheCCand significantlyaffected.
NCCprofilesbegintoconvergewithintheuncertaintiesinFigure5.
Applyingthisanalysistotheresultsfromthe1Tmodels,we
findameanmetalfractionfortheCCgroupsof0.29 0.03,where 4.2 ComparisontoRasmussen&Ponman(2007)
±
theerrorquoted isthestandarderror onthemeanmetalfraction,
AlthoughthedetailedabundanceprofilebehaviourofNCCgroups
whilstfortheNCCgroupsthemeanmetalfractionis0.16 0.02,
± hasnotbeenpreviouslyexamined,wecancomparethebehaviour
almostafactoroftwolower.Inthecaseofthe2Tmodels,abun-
of the CC abundance profiles here with those of RP07. The lat-
dancesarehigher, butthemeanmetallicityinCCsystemswithin
terworkbenefitsfromthehigherspatialresolutionavailablewith
0.3r500 is still double that for NCC groups. A key question is Chandradata,sowecannotdrawinferenceshereonthepresence
whetherthecentralmetalsseeninCCgroupsaremissinginNCC
ofthecentral(within0.01r500)dropinabundanceseenbyRP07.
groups, or whether they have just been mixed out to larger radii.
Wecanhowever,comparetheoveralltrendseenintheCCsystems.
FormostoftheCCgroups,wedonothavegoodmetallicityesti-
Thereisanoverlapof 10CCsystemsbetween thiswork andthe
mates outside 0.5r500. We therefore adopt an abundance of 0.18 sample of RP07, which further allows a comparison of the spec-
solaroutside0.3r500,correspondingtotheaveragebehaviour.We tral analysis methods for those systems in common. RP07 fitted
thenfindthemeantotalmetalmassinside0.3r500 tobetypically theirspectrawith2Tmodelswhereverthesegaveasignificantim-
one half of that in the radial range 0.3r500–r500. This is not an provementinfit,whichwasoftenthecasewithinthecoolcore.We
insignificantfraction,somixingoutthecentralmetalpeakshould
thereforeshowthecomparisonwithbothour2Tand1Tresults.
have a substantial impact on the outer regions. Thus, if the cen-
To enable a fair comparison, we convert the
tral metal peak has been mixed out to a large radius in NCCs, it
Grevesse&Sauval (1998) abundances presented by RP07 to
wouldbeexpectedtoleadtoasignificantriseinmetallicityinthe
Anders&Grevesse (1989); this requires dividing the former by
outer regions, compared with what is seen in CC groups. Within
a factor of 1.48 (as described by RP07). A further correction is
the limitsof our data, there isno evidence for this, except inthe
required to allow for the difference in the method of calculating
caseofHCG51.However,betterqualityspectraldataextendingto
r500 in the two samples, as the RP07 r500 values are typically
largeradiiisrequiredtofirmlyestablishwhether ornot amixing
1.14timesgreaterthanthevaluesusedhere.Wehavescaledthe
scenarioisviable. ∼
r500 values of the RP07 sample down by this factor to compare
to our work. We have again stacked the abundance profiles for
the CC groups, this time increasing the number of radial bins to
4.1 CC/NCCdefinition
allow a more thorough comparison withthe profile of RP07. We
The CC/NCC definition employed by Johnsonetal. (2009) com- alsonowcalculatethemedianineachbin,toavoidanybiasfrom
pared the temperature profile behaviour in the radial range 0– an individual group influencing the overall profile. Although the
0.05r500withthatintheradialrange0.1–0.3r500.Therefore,when meantrendsarewell-established(seeFigure5),individualgroups
weclassifyagroupasaCC,wearereferringtoaclassiccoolcore doshowsomedeviationsfromthesemeanprofiles.Toindicatethe
system, equivalent to the LCC systems of Sunetal. (2009), with degreeofscatterineachbininFigure6weplot(aserrorbars)the
a core typically extending to 0.1r500. With this definition, any medianabsolutedeviationineachradialbin.
∼
groups showing a central temperature drop on very small radial Figure 6 shows the stacked abundance profile for the CC
scales (< 10 kpc), would be classified as NCC. Such behaviour groups from the current sample under the 2T analysis, shown as
is seen in 20 per cent of systems in the Chandra sample of solidsquares, andthestacked abundance profilefromthesample
≈
Sunetal.(2009),termed‘coronae’classsystemsbySunetal.They ofRP07,shownasopencircles.Thepointsfromthisanalysistend
possessasmall coolregionlyingwithinthecentral galaxy. None tobehigherthanthoseofRP07,howeverthespreadofabundances
(cid:13)c 2010RAS,MNRAS000,1–15
8 R. Johnson,A. Finoguenov,T.J.Ponman,J. Rasmussen& A.J. R. Sanderson
2
1.
4
1. 1.1
0
2 1.
1.
9
0.
0 8
1. 0.
()anceZsolar0.8 ()anceZsolar0.60.7
d d
Abun0.6 Abun0.5
4
0.
4
0. 0.3
2
2 0.
0.
1
0.
0 0
0. 0.
0.01 0.05 0.1 0.5 1 0.01 0.05 0.1 0.5 1
r r500 r r500
Figure6.ThestackedabundanceprofilesoftheCCgroupsfromoursample Figure7.ThestackedabundanceprofilesoftheCCgroups(opencircles)
usingthe2Tanalysis(solidsquares),derivedfromthemedianabundancein andNCCgroups(filledsquares)fromthe2Tspectralfits,withverticaler-
eachradialbin,witherrorbarsthatcorrespondtothemedianabsolutedevi- rorbarsshowingthestandarderroronthemeanabundance,andhorizontal
ationtoshowthedegreeofscatterineachbin.Opencirclesshowtheresults errorbarsshowingtheradialwidthofthebin.Forcomparison,weshow
ofRasmussen&Ponman(2007),wherewehavere-scaledtheirabundances the mean abundance profiles from the cluster sample of Sandersonetal.
by1.48tomatchtheAnders&Grevesse(1989)abundancespresentedhere, (2009) in red, with open circles denoting CC clusters and filled squares
andhavere-scaledther500 valuesofRasmussen&Ponman(2007)toal- denoting NCC clusters. The horizontal error bars show the radial width
lowfordifferencesinthemethodofcalculation.Thedottedlineshowsthe of each bin, and vertical error bars show the standard deviation in each
medianabundancesfromthe1Tspectralfits. bin.Wehavere-scaledtheabundancesofSandersonetal.(2009)tomatch
theAnders&Grevesse(1989)abundancespresentedhere.Thedashedand
solidlinesshowthemeanresultsofour1TspectralfitsforCCandNCC
ineachbinismuchlarger.ItisworthnotingthatRP07useVAPEC groupsrespectively.
spectralmodelsinXSPEC,sothattheabundanceshowninFigure6
isactuallytheironabundance.WithintheRP07sample,thediffer-
encebetweenironabundance andthemeanmetallicityisatmost CC and NCC groups in our sample with the mean abundance
15%.SinceRP07usedamixtureof1Tand2Tspectralfitswithin profiles of a sample of 20 clusters, presented by Sandersonetal.
theirgroupcores,wealsoincludeour1TprofileintheFigure.In (2009). Thelatterprofileshave alsobeen split intoCC and NCC
general,theshapeofourmeanabundanceprofileisconsistentwith categories, and result from single–temperature fits to spectra ex-
thatofRP07,thoughthematchiscloserforour1Tfits. tractedfromannuli.Figure7showsthestrikingsimilaritybetween
theabundanceprofilesofCCandNCCclusters,incontrasttothe
situation in groups, where CC and NCC systems have distinctly
4.3 Comparisontoclusters differentprofiles.ComparingCCgroupstoCCclustersshowsCC
groupstohaveahighercentralpeak,whether1Tor2Tmodelsare
Recent work on the abundance profiles of CC and NCC clus-
employed, which may be explained by the increased dominance
tershasshownthemtoexhibitverysimilarprofiles.Forexample,
of the brightest group galaxy (BGG)in lower mass systems(e.g.
an analysis of Chandra data by Sandersonetal. (2009) showed
Lin&Mohr2004).NCCgroupshoweverhaveconsiderablyflatter
NCC clusters to show a similar decline with radius to CC clus-
abundanceprofilesthanNCCclusters.Wewillreturntothispoint
ters,andSivanandametal.(2009)findsteepabundance gradients
inSection5.
in9/12clusters,ofwhichonly4areCCs.Atintermediateredshift
(0.1 < z < 0.3), Baldietal. (2007) showed the abundance pro-
files of CC clusters to rise above those of NCC systems within
4.4 Lowabundancesystems
0.1r180, however, outside this radius, they found no significant
difference in the profiles of CC and NCC clusters. Earlier work Motivated by the challenge of determining the main driving fac-
byDeGrandi&Molendi(2001)andDeGrandietal.(2004)with torsthatleadtotheapparentbimodalityintheabundanceprofiles
BeppoSAX data showed almost flat abundance profiles in NCC presentedinSection4,wehavelookedforsystemsthatbuckthese
clusters, compared to steep abundance profiles in CC clusters. mean trends. We find four systems to have very low abundances
However,theNCCsampleusedintheBeppoSAX studyconsisted of less than 0.2 Z⊙ across the measured radial range. Three of
ofwellknown mergingclusters,whichprobablyaccounts forthe thesegroups areNCCs(HCG15, NGC4168 and A194) and one
differentprofilesinthesecomparedtomorerecentstudiesofNCC isaCCsystem(NRGb184).GiventheroleoftheBGGinestab-
clusters(S.Molendi,privatecommunication). lishingthecentralpeakinabundance(e.g.David&Nulsen2008;
InFigure7wecomparethemeanabundanceprofilesforthe Rasmussen&Ponman2009),wehypothesisethattheselowabun-
(cid:13)c 2010RAS,MNRAS000,1–15
Abundanceprofilesof groups 9
dancesystemshaverelativelysmall(i.e.lowerstellarmass)bright-
Table 2. The mean group temperatures (measured in the region 0.1–
est group galaxies,such that therelativeinjection ofmetalsfrom 0.3r500)from 1T spectral fits, and the 1.4GHzradio luminosity ofthe
theBGGislow. BGG.ThefinalcolumnshowswhetherthegroupwasclassifiedasCCor
WecanassessthisbycalculatingtheratiooftheK-bandlu- NCCbyJohnsonetal.(2009).
tmiminaotseittyheoKft-hbeaBndGlGumtointohseittyotoafltghaesBmGaGssswuistihnignK0.230rm50a0g.nWiteudeess- Group (kTe¯V) lo(gWLH1.z4−G1H)z Radioref. CC/NCC
from2MASS(Skrutskieetal.2006),assumingaK-bandabsolute
3C449 1.28±0.02 24.31 C02 NCC
magnitude for the Sun of 3.39 (Kochaneketal. 2001). The only A194 1.01±0.15 23.85 C02 NCC
systemforwhichwedonothaveaK-bandmagnitudefortheBGG HCG15 0.62±0.04 21.70 C02 NCC
isHCG51.Thegasmasscomesfromβ-modelfitstothegasden- HCG42 0.75±0.19 21.09 C98 CC
sityprofilesof theindividual groups(seeJohnsonetal.2009,for HCG51 1.16±0.13 – – NCC
moreinformation).SimplymeasuringthemeanLK(BGG)/Mgas HCG62 1.06±0.02 21.51 C05 CC
of these low abundance systems we find LK/Mgas = 0.38 HCG68 0.69±0.09 21.91 C02 NCC
0w.h0i7chLL⊙K,K/MMg−⊙as1,=co0m.7p4ar±ed0.t1o2thLe⊙,rKemMai−⊙nd1,erwohfertehqeusoatmedpelerrofo±rsr HHICCC1GG4599927 001...572990±±±000...200453 23––.02 C––98 NNCCCCCC
arethestandarderroronthemean.
NGC507 1.34±0.01 22.77 C02 CC
Thisindicatesthatthelowabundancesystemsdoindeedhave
NGC533 1.26±0.01 22.30 C02 CC
a smaller ratio of stellar to gas mass within 0.3r500. Is this suf- NGC2300 0.75±0.01 20.47 C02 CC
ficient to account for their lower metallicity? To assess this, we NGC2563 1.31±0.05 – – CC
calculate the ratio of integrated iron to total stellar mass, to see NGC4073 1.87±0.05 – – CC
whether itisabnormallylow inthelowabundance groups. Com- NGC4168 0.77±0.31 20.99 C02 NCC
putingtheproductofgasmassandmetallicitysummedoveraseries NGC4261 1.11±0.02 24.60 C02 CC
ofradialshellsoutto0.3r500,anddividingbytheK-bandlumi- NGC4325 1.01±0.01 – – CC
nosity of the BGG, gives an indication of the metal contribution NGC4636 0.77±0.01 20.97 C02 CC
NGC5044 1.21±0.01 21.66 C05 CC
fromtheBGG.Inthelowabundancesystems,themeanofthisra-
NGC5129 0.95±0.03 22.01 C02 CC
tioof‘metalmass’toLK,BGGis0.19±0.03Z⊙M⊙/L⊙,K,whilst NGC5171 1.21±0.05 – – NCC
fortheremainderofthesystems,itis0.59±0.08Z⊙ M⊙/L⊙,K, NGC5846 0.69±0.01 21.36 C02 CC
wheretheerrorsquotedarethestandarderrorsonthemean.This
NRGb184 1.37±0.09 23.92 C02 CC
shows that the lower stellar mass of the BGGs in the low abun- Pavo 0.77±0.12 – – NCC
dancegroupsisnotsufficienttoaccount fortheirlowmetalmass RGH80 1.16±0.02 23.40 C98 CC
–theratioofmetalmasstostellarmassisactuallylowerinthese SRGb119 1.34±0.07 23.90 C02 CC
systems.Thesameconclusionisarrivedatifweallowforthepos- SS2b153 0.83±0.01 21.66 C02 CC
siblecontributionofnon-centralgroupgalaxiestothemetalmass References:
within 0.3r500. Using the total B-band luminosities within r500 C98 –Condonetal.(1998)
fromJohnsonetal.(2009)tonormalisemetalmassweobtainara- C02 –Condon,Cotton,&Broderick(2002)
tioforthelowabundance systemsof0.21 0.06Z⊙ M⊙/L⊙,B, C05 –Croston,Hardcastle&Birkinshaw(2005)
±
whereasthemeanratiois0.91 0.12Z⊙M⊙/L⊙,Bfortheremain-
±
derofthesample.Weconcludethatthemembergalaxiesinthese
lowabundance groupscontributeanunusuallylowmetalmassto ExtragalacticDatabase(NED).Radiofluxeswerenotavailablein
theICMwithin0.3r500. all cases, and we further searched the NRAO VLA Sky Survey
(NVSS; Condonetal. 1998) around the BGG position for radio
sources.Theradiofluxeswereconvertedtoradioluminosities,and
4.5 AGNactivity
areshowninTable2.Thesamplewithavailableradiopoweresti-
AstatisticalstudyoftheeffectsofAGNactivityonthegasprop- matesconsistsof14CCsystemsand6NCCsystems.
ertiesofgalaxygroupsbyJethaetal.(2007)showedthatalthough TheobservedflatterabundanceprofilesinNCCgalaxygroups
AGNmayhaveanimpactonthelocalgasproperties,thelargescale comparedtoCCgroupssuggeststhatamixingprocessmaybeaf-
gasstructure appears not tobe significantlyaffected. Thesample fectingthegasdistribution.IfthesourceofthismixingwereAGN,
usedbyJethaetal.(2007)wasbiasedtowardshottersystemswith wemight expect acorrelation between aflatter abundance gradi-
larger X-ray luminosities than ours. The majority of systems in entandthepresenceofapowerfulradiosource.The1.4GHzradio
thesampleofJethaetal.(2007)showatemperaturedeclinewithin power measures current AGN activity rather than recent activity,
0.1r500(seefigure4inJethaetal.2007),indicatingthattheirsam- sothepossibilityofatimelagneedstobeborneinmind.InFig-
pleisdominated byCCgroups. Herewehavetheadvantage that ure 8 we plot the observed abundance gradient within the group
we can consider the effects of AGN activity on NCC systems as corefromthe2T fitsversus the1.4GHzradioluminosity for the
well. systems where this latter measurement was available, separating
A study of the effects of feedback on the 2dXGS sample thesystemsintoCCandNCCgroups. Wespecifythecoreabun-
(Johnsonetal. 2009) concluded that AGN are probably the dom- dancegradientastheratioofthemeanabundancemeasuredwithin
inant source of feedback, rather than supernovae, due to the lack 0.05r500 to that measured in the 0.1–0.2r500 radial range. This
ofextrametalsinsystemswithhigherlevelsoffeedback,butthat choiceismotivatedbytheobservationofapproximatelyflatabun-
muchofthisfeedbackmighthavetakenplaceatearlierepochs.To dance profiles inside 0.05r500 in CC groups, observed by RP07.
investigate the effects of current AGN activity in these systems, This also allows the abundance gradients to be measured across
we have extracted 1.4GHz radio fluxes for the BGGs from the thesameradialrangeinallsystems.ForthegroupNGC5129,no
references shown in Table 2, primarily through the NASA/IPAC data areavailable inthe range 0.1–0.2r500, so we take themean
(cid:13)c 2010RAS,MNRAS000,1–15
10 R. Johnson,A. Finoguenov,T.J.Ponman,J. Rasmussen& A.J. R. Sanderson
9
6
8 2.
4
2.
7
2
2.
6 2.0
Abundance gradient345 Abundance gradient1.21.41.61.8 Radio power
2 1.0 20 − 21.5
21.5 − 22
1 ngc5846 ngc5129 0.8 22 − 23
23 − 25
6
0.
0
4
0.
1
− 2
0.
20.5 21.0 21.5 22.0 22.5 23.0 23.5 24.0 24.5 0 1 2 3 4 5 6 7 8
log10 Lradio (1.4GHz) Temperature gradient inside peak
Figure8.Themeasuredabundancegradientwithin0.2r500 fromthe2T Figure 9. The abundance gradient (measured as explained in Sec-
spectralfits(seetext)asafunctionofthelogarithmic1.4GHzradiopower tion4.5)versusthetemperaturegradientwithinthetemperaturepeakfrom
ofthe brightest group galaxy. Open circles show CC systems, and filled Johnsonetal.(2009),fortheCCsystems.The14CCgroupswithavail-
squaresshowNCCsystems.NGC5129andNGC5846aremarkeddueto ableradiopowershavebeenbinnedbythelogarithmoftheir1.4GHzradio
thedifferenceinmethodologyforthecalculationoftheabundancegradient. power,asdescribedbythelegend.
abundanceintherange0.2–0.3r500astheoutermostmeasurement. tiontestbetweenthelogarithmic1.4GHzradiopoweroftheBGG
Given the drop in abundance withradius in theCC systems, this andthetemperaturedropinsidethecore(normalisedbythemean
should leadto an overestimate of the trueabundance gradient by temperature of the system), we find no significant correlation. In
35percent.ThegroupNGC5846alsodoesnotcontainanydata Figure 9 we show the abundance gradient (calculated as for Fig-
∼
inthelargerradialrange,soweusetheoutermostabundancemea- ure8)versusthetemperaturegradientintheCCsystems.Herewe
surementinstead,leadingtoapotentialunder-estimateoftheabun- havesplitthegroupsintofourbinsinthelogarithmofthe1.4GHz
dancegradient.ThesedatapointsareidentifiedinFigure8.Twoof radiopower.Lookingatthesetwoparametersinconjunctionwith
theNCCsystemswithmeasuredradioluminositieshavenoabun- theabundancegradientmeasurement,steepermetallicitygradients
dance measurements within0.05r500. Inthese cases, we adopt a occur inthecores of thesystemswithlower radio power, aswas
valuewithin0.05r500 equal totheinnermost measurement avail- suggestedbyFigure8.Figure9alsoconfirmsthatthetemperature
able.Thisassumes theinnermost abundance profileisflat,which gradientshowsnostrongtrendwithradiopower.
fromFigure5isareasonableassumption.Inthisscheme,alarger Tofurther investigatetherelationshipbetweenAGNactivity
numberonthey-axisinFigure8indicatesasteeperabundancegra- andabundanceprofiles,wesub-dividethe20groupsforwhichra-
dient. dio luminosities are available into ‘radio loud’ and ‘radio quiet’
The radioluminositiesof thebrightest group galaxiesinthe sub-samplesbasedonthemedianlogarithmicradioluminosityof
NCCgroupscoverasimilarrangetothoseintheCCgroups.Itis thewholesample(logL1.4GHz =21.96WHz−1).Thenumber of
thereforeimmediatelyclearthatcurrentAGNactivityisnotrespon- groupsineachcategoryisshowninTable3.Weshowthestacked
siblefortheobserveddifferenceinabundancedistributionbetween abundance profiles for the CC radio loud/radio quiet samples in
CCandNCCgroups.FortheCCgroups,wefindanticorrelationat Figure10, derived from the 2T fits. The small number of groups
the95%confidencelevelbetweenthecoreabundancegradientand in the radio loud and radio quiet NCC samples, and the diverse
radiopower.Acorrelationtestyieldsτ = 0.4,withap-valueof properties of these groups, preclude us from being able to draw
−
0.04.InthecaseofNCCgroups,thereisweakevidenceforapos- anyreliableconclusions ontheeffectof acentral radiosourcein
itivecorrelation,butthisisdrivenbythetwogroupswithhighest NCCsystems,soweshowthemeanNCCabundanceprofilefrom
radio luminosity, which have very poorly determined abundance Figure5inFigure10.Theprofilesof CCgroups withradioloud
gradients. Better data are therefore required to draw any conclu- and radio quiet BGGs are quite similar. In particular, the central
sions about any relationship beween radio power and abundance abundancelevels(within0.05r500)arecomparable,andbothsub-
distributioninNCCsystems. samples seem to show a relatively flat profile within this radius.
ConsideringjusttheCCgroups,wecanalsolookforanyim- ThelargestandarderrorsapparentinFigure5withintheinnerbins
pactfromthecentralradiosourcesonthetemperaturedistribution. reflect considerable group-to-group diversity, as is apparent from
Johnsonetal.(2009)calculatedthetemperaturegradientfrom1T examinationofFigure3.ItcanbeseenthatmanyCCgroupsshow
spectral models,measured fromthetemperaturepeak tothetem- aplateauordeclineinabundanceatsmallradius,whilstothersdo
peratureat0.01r500.Thisallowsacalculationofthetemperature not.Thisdiversitymakestheformalsignificanceofthecentralflat-
gradientinsidethetemperaturepeak.PerformingaKendallcorrela- teninginabundance marginal withinthestacked data. Itisworth
(cid:13)c 2010RAS,MNRAS000,1–15