Multiphase Signatures of Active Galactic Nucleus Feedback in Abell 2597

18 Pages·2017·10.36 MB·English

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Physics and Astronomy Faculty Publications Physics and Astronomy
2012
MMuullttiipphhaassee SSiiggnnaattuurreess ooff AAccttiivvee GGaallaaccttiicc NNuucclleeuuss FFeeeeddbbaacckk iinn
AAbbeellll 22559977
G. R. Tremblay
European Southern Observatory, Germany
C. P. O'Dea
Rochester Institute of Technology
S. A. Baum
Chester F. Carlson Center for Imaging Science
T. E. Clarke
Naval Research Laboratory
C. L. Sarazin
University of Virginia
SFoeello nwe xtth pisa agned f oard additdioitnioanl awl oaruktsh aotr:s h ttps://uknowledge.uky.edu/physastron_facpub
Part of the Astrophysics and Astronomy Commons, and the Physics Commons
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RReeppoossiittoorryy CCiittaattiioonn
Tremblay, G. R.; O'Dea, C. P.; Baum, S. A.; Clarke, T. E.; Sarazin, C. L.; Bregman, J. N.; Combes, F.; Donahue,
M.; Edge, A. C.; Fabian, A. C.; Ferland, Gary J.; McNamara, B. R.; Mittal, R.; Oonk, J. B. R.; Quillen, A. C.;
Russell, H. R.; Sanders, J. S.; Salomé, P.; Voit, G. M.; Wilman, R. J.; and Wise, M. W., "Multiphase Signatures
of Active Galactic Nucleus Feedback in Abell 2597" (2012). Physics and Astronomy Faculty Publications.
33.
https://uknowledge.uky.edu/physastron_facpub/33
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http://dx.doi.org/10.1111/j.1365-2966.2012.21281.x
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Published in Monthly Notices of the Royal Astronomical Society, v. 424, issue 2, p. 1026-1041.
This article has been accepted for publication in Monthly Notices of the Royal Astronomical Society ©:
2012 The Authors Published by Oxford University Press on behalf of the Royal Astronomical Society. All
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AAuutthhoorrss
G. R. Tremblay, C. P. O'Dea, S. A. Baum, T. E. Clarke, C. L. Sarazin, J. N. Bregman, F. Combes, M. Donahue,
A. C. Edge, A. C. Fabian, Gary J. Ferland, B. R. McNamara, R. Mittal, J. B. R. Oonk, A. C. Quillen, H. R.
Russell, J. S. Sanders, P. Salomé, G. M. Voit, R. J. Wilman, and M. W. Wise
This article is available at UKnowledge: https://uknowledge.uky.edu/physastron_facpub/33
Mon.Not.R.Astron.Soc.424,1026–1041(2012) doi:10.1111/j.1365-2966.2012.21281.x
Multiphase signatures of active galactic nucleus feedback in Abell 2597
(cid:2)
G. R. Tremblay,1,2,3 C. P. O’Dea,2,4 S. A. Baum,3,5 T. E. Clarke,6 C. L. Sarazin,7
J. N. Bregman,8 F. Combes,9 M. Donahue,10 A. C. Edge,11 A. C. Fabian,12
G. J. Ferland,13 B. R. McNamara,4,14 R. Mittal,3 J. B. R. Oonk,15 A. C. Quillen,16
H. R. Russell,14 J. S. Sanders,12 P. Salome´,9 G. M. Voit,10 R. J. Wilman11
and M. W. Wise15
1EuropeanSouthernObservatory,Karl-Schwarzschild-Str.2,85748GarchingbeiMu¨nchen,Germany
2DepartmentofPhysics,RochesterInstituteofTechnology,84LombMemorialDrive,Rochester,NY14623,USA
3ChesterF.CarlsonCenterforImagingScience,54LombMemorialDrive,Rochester,NY14623,USA
D
4Harvard–SmithsonianCenterforAstrophysics,60GardenStreet,Cambridge,MA02138,USA o
w
5RadcliffeInstituteforAdvancedStudy,10GardenStreet,Cambridge,MA02138,USA n
6NavalResearchLaboratoryRemoteSensingDivision,Code72134555OverlookAvenueSW,Washington,DC20375,USA loa
d
7DepartmentofAstronomy,UniversityofVirginia,POBox400325,Charlottesville,VA22904-4325,USA ed
8DepartmentofAstronomy,UniversityofMichigan,AnnArbor,MI48109,USA fro
9ObservatoiredeParis,LERMA,CNRS,61Av.del’Observatoire,75014Paris,France m
h
10PhysicsandAstronomyDepartment,MichiganStateUniversity,EastLansing,MI48824-2320,USA ttp
11DepartmentofPhysics,DurhamUniversity,DurhamDH13LE ://m
12InstituteofAstronomy,MadingleyRoad,CambridgeCB30HA n
13DepartmentofPhysics,UniversityofKentucky,Lexington,KY40506,USA ras
14PhysicsandAstronomyDepartment,WaterlooUniversity,200UniversityAvenueW.,Waterloo,ONN2L,2G1,Canada .ox
15ASTRON,NetherlandsInstituteforRadioAstronomy,POBox2,7990AADwingeloo,theNetherlands ford
16DepartmentofPhysicsandAstronomy,UniversityofRochester,Rochester,NY14627,USA jo
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Accepted2012May9.Received2012May8;inoriginalform2012March2 rg
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ABSTRACT rs
We present new Chandra X-ray observations of the brightest cluster galaxy (BCG) in the ity o
cool-coreclusterAbell2597(z=0.0821).Thedatarevealanextensivekpc-scaleX-raycavity f K
e
networkaswellasa15-kpcfilamentofsoft-excessgasexhibitingstrongspatialcorrelationwith ntu
c
archivalVeryLargeArrayradiodata.Inadditiontoseveralpossiblescenarios,multiwavelength ky
evidencemaysuggestthatthefilamentisassociatedwithmultiphase(103–107K)gasthathas Lib
beenentrainedanddredged-upbythepropagatingradiosource.Stemmingfromafullspectral rarie
analysis,wealsopresentprofilesand2DspectralmapsofmodelledX-raytemperature,entropy, s o
n
pressureandmetalabundance.Themapsrevealanarcofhotgaswhichinprojectionborders A
u
theinneredgeofalargeX-raycavity.Althoughlimitedbystrongcaveats,wesuggestthatthe gu
s
hotarcmaybe(a)duetoacompressedrimofcoldgaspushedoutwardsbytheradiobubble t 2
0
or(b)morphologicallyandenergeticallyconsistentwithcavity-drivenactivegalacticnucleus , 2
0
1
heating models invoked to quench cooling flows, in which the enthalpy of a buoyant X-ray 4
cavityislocallythermalizedasambientgasrushestorefillitswake.Ifconfirmed,thiswould
bethefirstobservationalevidenceforthismodel.
Key words: galaxies: active – galaxies: clusters: general – galaxies: clusters: individual:
Abell2597–galaxies:clusters:intraclustermedium–galaxies:starformation.
ronmentsthroughwhichtheypropagate.Observationsofbrightest
1 INTRODUCTION
clustergalaxies(BCGs)incoolcore(CC)clusterssuggestthatthe
Althoughanimportantcomponentinmodelsofgalaxyevolution, outflowing plasma can drive sound waves and subsonically exca-
little is known about the mechanical interaction between active vatecavitiesintheambientX-raybrightintraclustermedium(ICM;
galactic nucleus (AGN) outflows and the ambient gaseous envi- e.g.Sarazin1986),actingaslowerlimitcalorimeterstotheAGN
kineticenergyinput(Bo¨hringeretal.1993;Fabianetal.2000,2006;
McNamara et al. 2000, 2001; Blanton et al. 2001; Churazov
(cid:2)
E-mail:[email protected] etal.2001;Bˆırzanetal.2004;Formanetal.2005,2007;Nulsen
(cid:2)C 2012TheAuthors
MonthlyNoticesoftheRoyalAstronomicalSociety(cid:2)C 2012RAS
AGNfeedbackinAbell2597 1027
etal.2005).Alongwithawealthofsupportingcircumstantialevi- (2012).HerewedescribethetwonewChandraX-rayObservatory
dence,theseobservationsmotivatetheradio-modeAGNfeedback AXAFCCDImagingSpectrometer(ACIS)exposuresoftheA2597
paradigm, invoked at late epochs to inhibit catastrophic cooling BCG, taken in 2006 May for a total of 52.8 and 60.9 ks, respec-
flows that should otherwise drive extreme star formation rates in tively(ObsIDs6934and7329,PI:Clarke).Bothobservationswere
the BCG (e.g. reviews by Fabian 1994, 2012; Peterson & Fabian takeninVFAINT,full-frame,timedexposuremode.Anolder40-ks
2006;McNamara&Nulsen2007,2012).However,whilethecavi- Chandraexposure(ObsID922,PI:McNamara)wastakenin2000
tiesdemonstratetheprofoundimpactofjetsonambienthotX-ray JulyandoriginallypublishedbyMcNamaraetal.(2001)(hereafter
haloes,thephysicscouplingAGNmechanicalenergytoICMstruc- M01)inastudyoftheA2597ghostcavity(whichwewilldiscuss
tureandentropyremainpoorlyunderstood. later).ThisobservationwastakeninFAINT,full-frame,timedex-
Moreover,modelsinvokingradio-modefeedbacktoquenchcool- posure mode. As noted in M01, ObsID 922 was badly impacted
ingflowsignaturessuchasstarformationmustbereconciledwith byflaringevents,yieldingonly∼18ksofdatasuitableforspectral
observational evidence that, in several systems, the propagating analysis.Wehavereprocessedalloftheseobservationsinauniform
radio source triggers rather than inhibits star formation. Hubble manner,asdescribedbelow.
SpaceTelescope(HST)Far-Ultraviolet(FUV)observationsofsev- Thethreeobservations(ObsIDs922,6934and7329)wereob-
eral CC BCGs reveal knots of young stars preferentially aligned tained as primary data products from the Chandra Data Archive.
alongtheedgesofradiolobes–siteswheretheoutflowingplasma The data were reduced in version 4.2 of the CIAO environment Do
collideswiththeobservedambientcoldgas(e.g.Abell1795;Abell (Chandra Interactive Analysis of Observations; Fruscione et al. wn
2597; O’Dea et al. 2004; Tremblay et al. 2012, and references 2006) using version 4.3.1 of the calibration data base (CALDB). loa
d
therein).Manystudieshavesuggestedthatthejetpropagationfront The CIAO script chandra_repro was run for each observation to ed
canshockandcompressthesecoldclouds,inducingrapid,short- automate the creation of new level=1 and level=2 event files fro
m
durationstarbursts(e.g.Elmegreen&Elmegreen1978;Voit1988; by applying charge transfer inefficiency (CTI) correction, time- h
DeYoung1989;McNamara&O’Connell1993;O’Deaetal.2004; dependent gain adjustment, Pulse Height Amplitude (PHA) and ttp
Batcheldor et al. 2007; Holt, Tadhunter & Morganti 2008; Holt pixelrandomization,andstandardgradeandstatusfiltering.Only ://m
n
etal.2011).Massloadingofthejetcansimilarlyinducedecelera- thoseeventswithASCAgrades0,2,3,4and6areusedinthisanaly- ra
s
tionandbendingoftheradiosourceinregionsofhighgasdensity, sis.Backgroundlightcurvesforeachexposurewereobtainedfrom .o
x
whichcouldexplainthecompact,steepspectrumandbentFanaroff theACIS-S1back-illuminatedchip.TheCIAOscriptdeflarewas ford
&Riley(1974)classI(FRI)morphologiescommonlyassociated usedtocreategoodtimeinterval(GTI)temporalmasksrejecting jo
u
withradiosourcesembeddedindenseenvironments(e.g.O’Dea& countsassociatedwiththreesigmaflaresoverthemeanquiescent rn
Baum1986;Baumetal.1988). backgroundrate.Thisfilteringstrategyretainedonly∼18(outof40) als
.o
Progress in understanding these issues rests on a better grasp ksofflare-freedataforthe922observation.ObsIDs6934and7329 rg
of the complex ways in which AGN outflows interact not only werenotsignificantlyimpactedbyflaringevents,andnomorethan at U/
withtheirhotgaseousenvironments,butwiththecolderinterstellar 2ksforeitherobservationwererejected.Thecombinedeffectiveex- n
iv
medium(ISM)phasesaswell.InthispaperwepresentnewChan- posuretimeis150ks,andthecombinedflare-freeexposuretimeis e
rs
draX-rayObservatoryobservations,totalling150ksincombined 128ks. ity
ethffeeccteivnetreexopfotshuereCtCimcel,uosftetrheAbberilglh2t5e9st7c(lzus=ter0g.0a8la2x1y).(PBrCevGi)ouast usiAng0s.t5a–n7dkaerdVdemnceorpgyytfielctehrniwqausesa.pTphlieefdltuoxtihmeargedeusccerdipetxwpaosstuhreens of Ke
n
works have shown that the source exhibits extensive, multiphase used to create exposure maps for each data set. The observations tu
c
(103–107K)signaturesofAGN/ISMinteractions,includingX-ray were reprojected to a common World Coordinate System (WCS) ky
L
cavities,evidenceforgasentrainmentandjet-triggeredstarforma- tangent point, combined, and divided by their similarly repro- ib
tion(e.g.Sarazinetal.1995;Tayloretal.1999;O’Deaetal.2004; jected and combined exposure maps, creating exposure-corrected ra
Clarkeetal.2005;Oonketal.2010).InSection2wedescribethe 0.5–7keV mosaics suitable for spatial analysis. Soft (0.5–1keV), ries
o
observations,datareductionandourprocedureforthecreationof medium(1–2keV)andhard(2–7keV)combinedimageswerealso n A
2DspectralmapsfromthenewX-raydata.InSection3wepresent createdusingthisstrategy.Adaptivelysmoothedandunsharpmask u
g
u
spatial and spectral results, including general X-ray morphology, imagesweremadeusingtechniquesdiscussedinSection3.Merged s
t 2
radio/X-rayspatialcorrelations,surfacebrightnessandspectralpa- data are not suitable for spectral analysis, so X-ray spectra were 0
rameter radial profiles and a hardness analysis. In Section 4 we extracted from each individual observation and analysed simulta- , 20
1
present the 2D spectral maps of modelled X-ray gas properties neously in XSPEC version 12.5 (Arnaud 1996). We have also cre- 4
includingtemperature,entropy,pressureandmetalabundance.In ated 2D spatial+spectral maps of projected X-ray temperature,
Sections5and6wediscussthemainresultsofthispaper,namely pressure and metal abundance, following a procedure described
the‘coldfilament’and‘hotarc’features(respectively).Throughout below.
thiswork,weadoptH = 71h−1kms−1Mpc−1,(cid:3) = 0.27and
0 71 M
(cid:3)(cid:4)=0.73.Inthiscosmology,1arcseccorrespondsto∼1.5kpcat
theredshiftoftheA2597BCG(z=0.0821).Thisredshiftcorre-
2.1 CreationofX-rayspectralmaps
spondstoanangularsizedistanceofD ≈ 315Mpcandalumi-
A
nositydistanceofD ≈369Mpc.AdiscussionofthesenewX-ray UsingthespatiallyresolvedChandraspectroscopy,wehavecreated
L
observationsinthecontextofICMcoolingandAGNheatingcan 2DmapsofprojectedX-raytemperature,pseudo-entropy,pseudo-
befoundinacompanionpaper(Tremblayetal.2012). pressureandmetalabundance.Webrieflydescribehowthesemaps
werecreatedbelow,butreferthereadertoSection3formoredetails
one.g.howspectraareextractedandmodelled.
2 OBSERVATIONS AND DATA REDUCTION
Tomakethespectralmaps,theexposure-correctedmosaicwas
Asummaryofallnewandarchivaldataused(directlyorreferen- cleanedofcontaminatingpointsources,croppedtoincludeonlythe
tially) in this analysis can be found in table 1 of Tremblay et al. inner 80×80arcsec2 (120×120kpc2),thenpassedthroughthe
(cid:2)C 2012TheAuthors,MNRAS424,1026–1041
MonthlyNoticesoftheRoyalAstronomicalSociety(cid:2)C 2012RAS
1028 G.R.Tremblayetal.
CONTBIN1adaptivebinningalgorithmdescribedbySanders(2006).
3 X-RAY SPATIAL AND SPECTRAL RESULTS
Thecodelocatesthebrightestpixelintheimageandcreatesaspa-
tialbinarounditbyincludingallneighbouringpixelsoflikesurface
3.1 GeneralX-raymorphology
brightnessuntilauser-definedsignal-to-noiseratio(S/N)threshold
ismet,anditerativelymovesoutwardsfollowingthesameproce- Previous X-ray studies have been published for A2597 using the
dure.FortheX-raytemperatureandemissionmeasuremaps(used 40-ks(18ksofgoodtime)Chandraobservation922(e.g.M01and
in the pseudo-entropy and pressure maps), we set this threshold Clarkeetal.2005,hereafterC05).M01wasthefirsttoreporton
tobeS/N=30,or(cid:2)302 =900counts.Forthemetalabundance thewesternandnorth-easternghostcavitiesinferredfromlocalized
map, we set it to S/N = 70. The shape of each spatial bin was depressions in the X-ray surface brightness. Later work by C05
constrainedsothatitslengthcouldbeatmosttwotimesitswidth extendedthisanalysistoincludeastudybetweenX-raymorphol-
(toprevent‘stripe’-likebinswhichwouldsampleanunreasonably ogy and Very Large Array (VLA) radio observations at 8.4GHz,
largespatialcross-sectionofmultiphaseclustergas).Theresultisa 1.3GHzand330MHz.ThatworkdescribedanX-ray‘tunnel’ap-
spatiallybinnedimagethatfollowsthesurfacebrightnessdistribu- parent in their unsharp mask of the 922 data. Roughly 22arcsec
tion.Inadditiontothecontourbinnedimage,thealgorithmcreates (33kpc) in projected length and 1.5arcsec (2.3kpc) in projected
abinmapwhichweusedwithJ.Sanders’make_region_files radius,thetunnelappearedtoconnectthepeakoftheX-raysurface
codetocreateCIAO-compatibleregionfilesforeachofthe277in- brightness distribution, cospatial with the radio and BCG optical Do
dividualspatialbinscreatedforourdatabytheCONTBINcode.The core,withtheM01westerncavity.Itwasnotapparentwhetherthis wn
individuallevel=2eventfilesforChandraObsIDs6934and7329 was a discrete feature, or was part of a larger cavity encompass- loa
d
(whichweresimilarlycleanedofpointsources)werethenspatially ingboththetunnelandtheM01cavity.Extended330-MHzradio ed
reprojectedtoidenticalpositionsusingthemergedimageasaco- emissionwasobservedtobecospatialwithbothfeatures. fro
m
ordinatereference.Theregionfilescreatedfromthebinmapwere In Fig. 1 we present the new, combined 0.5–7keV data. The h
then ported to each of the two event files. A script was used to left-handpanelshowstheexposure-correctedmosaicwithnospa- ttp
iterativelyextractthesourcespectrum,backgroundfileandcreate tialbinningorsmoothingapplied.Theright-handpanelshowsthe ://m
n
associatedresponsefiles(ARF/RMF)foreachofthe277spatialre- mergeddataadaptivelysmoothedwithavariablewidthGaussian ra
s
gionsoneachofthetwoeventfiles.Thecorrespondingsourceand kernelwhosesizeself-adjuststomatchthelocaleventdensity.Black .o
x
background spectra from like regions on the two exposures were surfacebrightnesscontoursareoverlaidtomakeindividualfeatures fo
then added together using the mathpha tool in CIAO, and average easiertoview.Theinnermostcontourmarksafluxof4.6×10−7 rdjo
responses were created using addarf and addrmf from FTOOLS. photonss−1cm−2pixel−1,andmovesoutwardswithadecrementof urn
The summed spectra were then regrouped to 15 count bins, and 2.0×10−8photonss−1cm−2pixel−1.Bothpanelssharethesame als
theBACKSCALandEXPOSUREheaderkeywordswereupdated. scale,withafieldofview(FOV)of∼60×60arcsec2,correspond- .org
Tsahmisepcrhoicped(wurheicishoisnltyruveiafbolreOifbsthIDesex6p9o3s4uraensdw7e3r2e9t)a.kTehneo1n8t-hkes iRnAgt=o9203h×259m019ks.p7c52.aTndheDFeOc.V=is−c1e2n◦t0re7d(cid:6)2o6n(cid:6).(cid:6)9th(eJ2X00-r0a)y.Acesnwtriotihdaaltl at Un/
(goodtime)922datasetwasthereforenotusedinthispartofthe figurespresentedinthispaper,northisupandeastistotheleft. ive
rs
analysis. TheX-raysurfacebrightnessdistributionishighlyanisotropic, ity
MeAwne–XKSPaEaCstrva1–2L.i5ed(aAhrlnthauerdm1al9p9l6a)smTaCmLosdcerlisp(tcawllaesdMusEedKAtoLfiint aanxdiseoxfttehnedBedCGalostnegllaarpisoospithioontesan(wglheic(hPAli)etohnatamPAat∼ch−es4t5h◦e,wmhaejorer of Ke
n
XSPEC),absorbedtoaccountforGalacticattenuation(i.e.WABS× norththrougheast,orcounterclockwise,isthepositivedirection). tu
c
MEKAL). These models were fitted simultaneously to the two ThespatialanisotropyoftheX-rayemissionseemstobeconfined ky
L
grouped,background-subtractedspectraextractedfromeachofthe tothescaleoftheBCG,astheX-rayisophotesassumeasmoother ib
matchedregionsofthetwoexposures.Foreachfit,thesourcered- ellipticalshapeintheoutermostregions. ra
fsrhoizftewnatostfihxeeGdatolazct=ic0v.a0l8u2e1o,ft2h.e4h8y×dr1o0g2e0nccmo−lu2m(Mn0d1en),saitnydNthHewgaass sioAnsissedeinstirnibFuitge.d1i,nthaebinuntteerrmflyo-sltik2e0sahrcaspeec,owfitthhet0w.o5–h7igkheVsuermfaicse- ries on A
temperaturekT,abundanceZandnormalizationN (effectively brightnessknots∼1arcsecWand∼3arcsecSEoftheX-raycen- u
MEK g
u
theemissionmeasure)wereallowedtovary.Thefitswereruniter- troid. The knot 1arcsec west is approximately cospatial with the s
ativelytominimizetheχ2statistic.Thebest-fittingparameterskT, radiocore.AfractionoftheX-rayemissioninthisknotstemsfrom t 20
Z,NMEKandtheircorrespondingupperandlower90percentcon- theweakpointsourceassociatedwiththeAGN.Twosharpdeficits , 201
fidenceintervalswerewrittentoindividualfileslinkedtotheircor- ofX-rayemission∼2arcsecNEand∼2arcsecSWdefinetheinner 4
respondingspatialbin.J.Sanders’scriptpaint_output_images ridgesofthe‘butterflywings’.Oneofthemostprominentfeatures
wasthenusedtorescalethespatialbinsintheCONTBINoutputim- visibleinFig.1isa10-arcsec(∼15kpcinprojection)filamentex-
agebytheirassociatedbest-fittingparameters,producingprojected tendingalongaPA≈55◦,roughlyperpendiculartothemajoraxis
temperature,emissionmeasureandabundancemaps.Aprojected ofthebutterflyfeatureandaligned(inprojection)alongtheminor
pseudo-pressure map was then created by multiplying the square axis of the BCG stellar isophotes. The western edge of the M01
rootoftheemissionmeasuremap(whichisproportionaltobutnot ghostcavityisfaintlyseen∼18arcsecwestand5arcsecsouthof
exactly the density, which requires an uncertain volume assump- thecentre.
tion)bythetemperature(kT)map.Themapswerethenadaptively In Fig. 2 we show the same 0.5–7keV data processed in
smoothedusingthesamevariable-widthGaussiankernelsizesas two ways: (1) a residual image made by subtracting a 30-arcsec
usedforthesmoothedsurfacebrightnessmapshownintheright- Gaussian smoothed image from the adaptively smoothed image
handpanelofFig.1. shownintheright-handpanelofFig.1,and(2)amoreconventional
unsharpmaskmadebysubtractinga20-arcsecGaussiansmoothed
imagefroma5-arcsec(non-adaptive)Gaussiansmoothedversion.
Thesubtracteddataarethendividedbythesumofthetwoimages.
1http://www-xray.ast.cam.ac.uk/papers/contbin/ Regions of X-ray surface brightness excess over the subtracted
(cid:2)C 2012TheAuthors,MNRAS424,1026–1041
MonthlyNoticesoftheRoyalAstronomicalSociety(cid:2)C 2012RAS
AGNfeedbackinAbell2597 1029
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Figure1. Leftpanel:exposure-corrected(fluxed)0.5–7keVimageofthethreemergedChandraexposures922,6934and7329.NoGaussiansmoothing ra
s
or pixel binning has been applied. Right panel: 0.5–7keV X-ray surface brightness map, smoothed with an adaptive Gaussian kernel. Black contours .o
x
havebeenoverlaidtobettershowthespatiallyanisotropicnatureoftheemission.Theinnermostcontourmarksafluxof4.6×10−7 photonss−1 cm−2 fo
pixel−1,andthecontoursmoveoutwardswithafluxdecrementof2.0×10−8 photonss−1 cm−2 pixel−1.BothpanelsshareanidenticalFOV,centredat rdjo
RA=23h25m19s.75andDec.=−12◦07(cid:6)26(cid:6).(cid:6)9(J2000). urn
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Figure2. Twounsharpmaskimagesofthemerged150-ksChandra0.5–7keVobservation.Theleft-handpanelwasmadeviasubtractionofa20-arcsec
Gaussiansmoothedversionoftheimagefromtheadaptivelysmoothedversion.Theversionintherightpanelwasmadebysubtractingthesame20-arcsec
Gaussiansmoothedversionoftheimagefroma5-arcsecGaussiansmoothedversion,thendividingbythesumofthetwoimages.Inthechosencolour
scheme,regionsoftheX-raysurfacebrightnessexcessoverthesubtractedsmoothedcountsappearinred/orange,whiledeficitsappearinblack.330-MHz
VLAcontourshavebeenoverlaidingreen,whilethe1.3-GHzradiocontoursareplottedinblue,andthe8.4-GHzradiocontoursappearinblack.Allofthe
radiodataarefromClarkeetal.(2005).Notehowtheextended330-MHzemissioncorrespondsinbothlinearextentandprojectedPAwiththeapparentX-ray
cavityconsistingoffeatures(1)and(2),aslabelledintherightpanel.Notealsothatthenorth-easthookofthe1.3-GHzemission(blue)isalignedwiththe
‘bottom’ofthe15-kpcX-rayfilament.Themajormorphologicalfeatureswhichwillbethesubjectoffurtherspatialandspectralanalysishavebeenlabelled
1–6intherightpanel.Althoughwelabelthemseparately,wedonotmeantoimplythatfeatures1and2arenecessarilydiscrete.Rather,feature1islabelled
separatelytoenableaclearercomparisonwiththeM01‘ghostcavity’.Features1and2maywellbeonelargercavity.Theringfeaturesseenintheleft-hand
panelareartefactsfromsubtractingimageswithdifferentsmoothinglengths.
(cid:2)C 2012TheAuthors,MNRAS424,1026–1041
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1030 G.R.Tremblayetal.
smoothbackgroundappearinwhite,whiledeficits(cavities)appear 1999;O’Deaetal.2004;Oonketal.2010).The1.3-GHzemission
in black. Both panels are on the same scale, with identical 50 × extendedalongthebottomhalfofthe15-kpcX-rayfilament(feature
50arcsec2(75×75kpc2)FOVs.Weoverlayradiocontoursonthe 5inFig.2)maybeevidenceforthedredge-upoflowertemperature,
left-hand panel, which we will discuss later. These two edge en- high-densitykeVgasbythepropagatingradiojet.Oonketal.(2010)
hancement methods (particularly method 1) are inherently noisy, reportedhigh-velocity(andvelocitydispersion)streamsofH and
2
andintroduceartefactsthatcomplicatequantitativemorphological HII coincident with the southern edge of the northern 8.4-GHz
analysis. Significance of the observed features must therefore be radiolobeandapproximatelyalignedwiththeprojectedVLBAjet
estimated from the unprocessed data. We show these mostly as axis. The jet may therefore be dynamically interacting with both
viewingaidsforthemajormorphologicalfeatures. thehotandwarm/coldphasesoftheISM.Wewillinvestigatethese
By comparing unsmoothed counts in like-sized regions at the possibilitiesinSection5.
samecluster-centricradius,wefindsixdiscretefeaturesassociated
with (cid:2)10σ deficits or excesses relative to the local mean. These
3.3 X-raysurfacebrightnessprofile
featuresarelabelled1–6intheright-handpanelofFig.2.Thispaper
discusses feature 5, the ‘cold filament’, while energetics analysis In Fig. 3 we plot azimuthally summed X-ray surface brightness
of the X-ray cavities is discussed in a companion paper on AGN againstprojectedradius,usingfluxesextractedfromnarrowconcen-
heatingandICMcoolinginA2597(Tremblayetal.2012). tricannulispanning∼5–100kpc.Wefitbothsingularandadditive Do
w
two-componentLorentz1D‘beta’modelswithavaryingpowerlaw n
lo
3.2 RadioandX-rayspatialcorrelations (beta1dinCIAOSHERPA)tothedata,whereinthesurfacebrightness ad
(cid:7) atprojectedradiusrvariesas ed
I3tin3v0ethl-yMe).lHeWfzte-VhdaLonAdnoprtaasndheioolwocfothnFetiogiun.rn2sewrimneoboslvtaec1rk.l3a,-ybGl8Hu.e4z-aGannHddz3g,3r1e0.e3-nM-G(HHrezzscpaoenncd-- (cid:7)XX(r)=(cid:7)X(0)(cid:2)1+(cid:3)rr (cid:4)2(cid:5)(−3β+1/2). (1) http from
tourstoallowthehigherfrequencycontourstobeclearlyvisible. 0 ://m
AsnotedbyM01andC05,thenorthernandsouthernlobesofthe Here, (cid:7)X(0) is the central X-ray surface brightness and r0 is the nra
8.4-GHzsource(blackcontours)areboundedtothewestandeast coreradius.Typically,theICMingalaxyclustersiswellfittedby s.o
bydeficitsofX-rayemissionassociatedwithfeatures6and2,re- models with β ≈ 0.6 (Sarazin 1986). Our results are consistent xfo
spectively.Beyondthis,itisdifficulttodiscernwhetherornotthe with this: if we fit a one-component beta model, shown in the rdjo
8.4-GHz lobes are interacting with the keV gas on these scales. left-hand panel of Fig. 3, we find β = 0.633 with core radius urn
N8.o4-GXH-razylocbaevsi,titehsoaurgehotbhsiserlvaecdktoofbeeviddierneccetlyshcoouslpdantioatl bweitihnttehre- ar0dd=iti1v6e.4twaorc-sceocm(poorn∼en2t4bkeptca).mAodfealr,bwethtiecrhfiwtiespolbottaiinnedthewirtihghatn- als.org
pscreatleedswasoeuvldidbenecveeoryfadbifsfiecnuclet.tAondyetceacvtitgiievsetnhaatcmoamybeinxaisttioonnothfe(sae) hfiatnwdipthanaelcionrFeigra.d3iu(rsedoflinr0e).=Th1i9s.1maordceselcco(nosris∼ts2o9fkapβc)=an0d.68a6n at Un/
thecompactnessoftheradiosourcecomparedtotheX-rayemis- innersteepcomponent(β =10)tofitthecusp(yellowlines).The ive
sionand(b)agreatdealofinterveningkeVgasalongthelineof smalldeviationsbetweenthemodelanddataarise(inpart)because rsity
swigohutl.dWbeeeaxspseocctiathteadtawniythcasvuirtfieasceasbsroicgihattneedswsidthectrheem8e.4n-tGsHofzalofbeews tahzeimauntnhualliafrvoemragwehoicfhXt-hreayspfleucxtreasatrheatexvtarrayctsetdroenfgfelyctaivsealyfugnivcetioann of Ke
n
per cent at most, strongly limiting their detectability. Past litera- ofpositionangle,owingtothemorphologicallydisturbednatureof tu
c
turepresentsstrongevidence(e.g.Koekemoeretal.1999;O’Dea theX-raygas.Intheplots,errorsbarsareshown,thoughdifficult ky
etal.2004)thatthe8.4-GHzsourceisdynamicallyinteractingwith toseebecausetheyaregenerallysmallerthanthedatapoints. Lib
the∼104Kemission-linenebula,whichwewilldiscusslater. ra
The330-MHzVLAA-configurationobservation(ingreencon- ries
3.4 0.5–7keVspectrumfromacentral100-kpcaperture o
tours)doesnotresolvestructuresatthescaleofthe8.4-GHzsource, n A
thoughaprominentarmofemissionextends∼70kpctothewest We extract a spectrum from the individual flare-filtered Ob- u
g
u
(projected)instrongspatialcorrelationwiththewesternlargecavity sIDs 6934 and 7329, using a single circular aperture with a s
(feature1+2).Itisworthnotingthatthesymmetric50pcscalejets 63.3-arcsec (100kpc) radius encompassing most of the sharply t 20
intheVeryLongBaselineArray(VLBA)mapofTayloretal.(1999) peakedcentralX-rayemission.Priortothis,weremovedcontami- , 20
areapproximatelyaligned(within∼5◦)withthemajoraxisofthe natingpointsources.ThespectrawereextractedusingtheCIAO4.2 14
westernlargecavityandtheextended330-MHzemission(though scriptspecextract,andcount-weightedresponsematriceswere
thisofcourseinvolvesacomparisonatvastlydifferentscales).The generatedforeachextraction.
blue 1.3-GHz contours are extended along the same axis as the Using simultaneous fitting techniques in XSPEC, we fit a va-
330-MHzeasternextension,theprojectedVLBAjetaxis,thewest- riety of models to the total 0.5–7keV spectrum extracted from
ern large cavity, as well as ∼8kpc along the bottom half of the the 100-kpc aperture. The most simple of these is a MEKAL
15-kpc X-ray filament (feature 5). The NE 1.3-GHz hook, which model that has been absorbed to account for attenuation by the
is∼15kpcfromtheradiocore,alsocoverstheC05filamentbase galactic hydrogen column (WABS × MEKAL). We also fit ab-
cavity(feature6).Thereisalsoa∼1-kpcextensiontotheSW,into sorbed two-component MEKAL models (WABS × [ MEKAL +
thebottomopeningofthewesternlargecavity. MEKAL]) as well as the standard cooling flow model in XSPEC
Theprojectedspatialcoincidenceofallofthesefeaturesisstrong (WABS × MKCFLOW). Finally, we fit a ‘reduced’ cooling flow
evidenceforacommon,currentjetaxis.WhilethePAofthe8.4- model WABS × [MEKAL + MKCFLOW] (e.g. Rafferty et al.
GHz source is offset from this axis, it is the exception, and may 2006), in which the high-temperature MKCFLOW parameter is
arisefromdynamicalfrustrationofthejetasitpropagatesamidthe tiedtotheMEKALkT parameter.Thephysicalmotivationbehind
densemolecularmediumharbouringtheemission-linenebula(this thismodelisthatAGNheatingmaintainsthebulkofthegasatthe
has been discussed by e.g. Sarazin et al. 1995; Koekemoer et al. ambienttemperature(fittedbytheMEKALcomponent),whilethe
(cid:2)C 2012TheAuthors,MNRAS424,1026–1041
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Figure3. X-raysurfacebrightnessprofilesextractedfromaseriesofconcentricannulispanningfromthecentralregionsoutto100kpc.(Leftpanel:a lo
a
d
one-componentbetamodelhasbeenfitted.Rightpanel:atwo-component(additive)betamodelhasbeenfitted,yieldingbetteroverallcorrespondencetothe e
d
measuredprofile.Theadditivetwo-componentmodelisinred,whilethetwoindividualcomponentstothemodelareshowninorange. fro
m
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ttp
Table1. Simultaneousspectralfitstothe0.5–7keVX-rayspectrumextractedfromacentral100-kpcaperture.Priortoextraction,atemporalfilterwasapplied ://m
tothedatatorejectflaringevents,andcompactsourcesassociatedwithotherclustermembersaswellasthecentralweakpointsourceassociatedwiththe n
AGNwereremoved.Thespectrawererebinnedusinga30-countthreshold.Observation922hasbeenexcludedfromspectralanalysisduetosignificantflaring ras
eventsandhighbackgroundlevels.Symmetric1σ confidenceintervalsareshownonfitparameters.Parametersthathavebeenfrozentoaspecificvalueprior .ox
tofittingareshowninparentheses.Inthelastmodel,WABS×[MEKAL+MKCFLOW],wetiethehigh-temperatureMKCFLOWparametertotheMEKAL ford
kTparameter,followingsimilar‘reduced’coolingflowmodellingintheliterature(e.g.Raffertyetal.2006;Russelletal.2010). jo
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a
XSPECmodel (×102N0Hcm−2) (kkTelVow) k(kTehVigh) Ab(usonldaarn)ce ME(K×A1L0−n2o)rm. MK(MC(cid:7)FLyOr−W1)M˙ R(eχd.2c/dhoifs)q. ls.org
(1) (2) (3) (4) (5) (6) (7) (8) a/
t U
WABS×MEKAL 1.5±0.12 ··· 3.42±0.02 0.43±0.01 1.501±0.009 ··· 745/735=1.014 niv
WABS×MEKAL 1.63±0.19 ··· 3.39±0.04 (0.4) 1.524±0.008 ··· 754/736=1.025 ers
WABS×MEKAL (2.48) ··· 3.31±0.03 (0.4) 1.55±0.005 ··· 807/737=1.096 ity
WABS×[MEKAL+MEKAL] (2.48) 2.68±0.13 6.01±1.05 (0.4) 1.10and4.57±2.06 ··· 759/735=1.032 of K
WABS×MKCFLOW (2.48) 1.88±0.07 5.33±0.16 (0.4) ··· 497±33 763/736=1.04 e
n
WABS×MKCFLOW 1.59±0.17 1.87±0.08 5.61±0.17 (0.4) ··· 454±29 707/735=0.96 tu
c
WABS×[MEKAL+MKCFLOW] (2.48) (0.1) 3.47±0.05 0.43±0.018 1.47±0.0002 22±5 740/739=1.008 ky
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ib
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s
MKCFLOWcomponentmodelsresidualcoolingfromthatambient on
3.5 Hardnessanalysis A
temperature(hencetheparametersharing)below0.1keV(towhich u
k0T.0l8ow21i.s fixed). In all cases, the source redshift was fixed to z = IinneFnige.rg5ywspeacsheofworstohfet (a0d.a5p–t1ivkeelVy)smthoroouthgehdhcaormdb(i2n–e7dkCeVha)ncdurtas gust 20
Results from our modelling are shown in Table 1. As evident data. In each panel we overlay the 8.4-GHz radio map in black , 20
incolumn8ofthetable,thefitsareuniformly‘good’intermsof contours, which for reference is ∼10kpc from end-to-end. The 14
reducedχ2,indicativeofthedegeneracythatalmostalwaysarises previouslymentioned15-kpcNEfilamentbecomesfainteratsuc-
fromthistypeofX-rayspectralfitting.Thelastlineofthistable cessivelyharderslicesinenergyspace,andeffectivelydisappearsin
listsresultsfromfittingthe‘reduced’coolingflowmodel,WABS× therightmostpanel.Thefilamentisthereforearelativesoftexcess
[MEKAL+MKCFLOW],whichhasbeenusedfrequentlyinre- andislikelytobecolderthanthesurroundinggas.Thebutterflyfea-
centliterature(e.g.Russelletal.2010).WeshowthisfitinFig.4 turealsolosesmuchofitsNE–SWwidthathigherenergieswhile
(greenline).Theindividualadditivemodelcomponents(MEKAL retainingeffectivelythesameextensionalongtheNW–SEaxisthat
andMKCFLOW)areshowninredsolidlinesandlabelledaccord- isalignedwiththemajoraxisoftheBCGstellarisophotes.Wehave
ingly.Thehigh-temperatureparameterintheMKCFLOWcompo- alsocreatedahardnessratiomap,butthiswillbediscussedinthe
nenthasbeentiedtotheMEKALambienttemperaturecomponent followingsection.Inthe1–2keVpanel,wehavemarkedtheloca-
tosimulatearesidualcoolingflowproceedingatlowlevelsfromthe tionofthe‘hotarc’,afeaturewhichwillbediscussedinSections4
hotX-rayatmosphere.Fitresidualsareshowninthebottompanel and6.
usingthesamecolourcoding.Theyreachan∼8percentmaximum WenotethatsoftX-rayemissionalonglinesofsightthatpass
attheFeL1-keVpeak.Wediscusstheresidualcoolingflowmodel throughthegalaxymidplanesuffersmoreattenuationfromthein-
forA2597atgreaterlengthinTremblayetal.(2012). trinsichydrogencolumnthandoeshardX-rayemission.Moreover,
(cid:2)C 2012TheAuthors,MNRAS424,1026–1041
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Figure4. 0.5–7keVX-rayspectrumoftheinnermost100kpcoftheA2597BCG,extractedfromChandraobservations6394(blackopencircles)and7329 f K
(blueclosedcircles).Thespectrahavebeenextractedindependently,groupedusinga30countbinsize,backgroundsubtracted,andfittedsimultaneouslyafter e
n
removalofcontaminatingsources.Areducedcoolingflowmodel(greensolidline)hasbeenfittedtothedata(WABS×[MEKAL+MKCFLOW]inXSPEC). tuc
k
Theindividualadditivemodelcomponents(MEKALandMKCFLOW)areshowninredsolidlinesandlabelledaccordingly.Thehigh-temperatureparameter y
L
intheMKCFLOWcomponenthasbeentiedtotheMEKALambienttemperaturecomponenttosimulatearesidualcoolingflowproceedingatlowlevelsfrom ib
thehotX-rayatmosphere.Fitresidualsareshowninthebottompanelusingthesamecolourcoding.Theyreachan∼8percentmaximumattheFeL1-keV ra
peak.SeethelastentryinTable1formodelparametersassociatedwiththisfit.Notethatothermodelfitspresentedinthesametableyieldsimilarresultsin ries
termsofreducedχ2,illustrativeofthedegeneracyinherentinthissortofX-rayspectralfitting. on
A
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0
, 2
0
1
4
Figure5. TheadaptivelysmoothedChandraimageofA2597shownatvariousslicesinenergyspace,including(fromlefttoright)‘total’(0.5–7keV),‘soft’
(0.5–1keV),‘medium’(1–2keV)and‘hard’(2–7keV)emission.Inblackcontours,weoverlaythe8.4-GHzradiocontoursofPKS2322−122,andinwhite
contoursweoverlayastellarisocontourfromtheHST R-bandobservationofthehostgalaxy.Theblacklineatthebottomleftcorneroftheleftmostpanel
marksadistanceof10arcsec(15kpc).NotethatthemajoraxisofthehostgalaxystellarisophoteisalignedalongthesamepositionangleastheX-raymajor
axis.Thebrightfilamentwhichextends15kpcNEfromthecentreinthetotalandsoftpanelsiseffectivelyabsentintherightmosthardpanel.Thefilamentis
thereforeasoftexcess,colderthanthesurroundinggas.ThehardX-ray‘disc’evidentintherightmostpanelisalignedinprojectionwiththeisophotalmajor
axisofitshostgalaxy’sstellarcomponent.
(cid:2)C 2012TheAuthors,MNRAS424,1026–1041
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AGNfeedbackinAbell2597 1033
asthelineofsightmovesawayfromtheprojectedmidplane,the same∼60×60kpc2 FOVcentredontheX-raycentroidatRA=
absorbinghydrogencolumngetssmaller,resultinginsmallerhard- 23h25m19s.75 and Dec. = −12◦07(cid:6)26(cid:6).(cid:6)9 (J2000). East is left and
nessratios.Itisthereforedifficulttobreakthedegeneracybetween northisup.
(a)truespatialdistributionofsoftversushardX-rayemittinggas Wefirstnotethattheoveralltemperaturegradientisreasonably
and(b)preferredsoft-endabsorptionbytheBCGhydrogencolumn. consistentwiththeprojectedradialtemperatureprofile(Fig.6,top
Byiterativelyincreasingthemagnitudeofthephotoelectricabsorp- left)overthesameradius.Weobservetwosignificantspatialfluctu-
tioncomponentinaWABS×MEKALfittotheX-rayspectrum, ationsfromtheazimuthallyaveragedtemperaturegradient,namely
wehaveestimatedthatahydrogencolumnof(cid:2)1023 cm−2 would the ‘cold filament’ and ‘hot arc’ features, which are outlined and
berequiredtoattenuateenoughofthesoftX-rayfluxtogiverise labelledaccordinglyinFig.8.
to such confusion. Such a high column density is not consistent IncomparingthetopleftpanelwithFig.2,itcanbeseenthat
withresultsfromourX-rayspectralmodelling,asdiscussedinthe theopeningofthehotarcborders,inprojection,theeasternedge
sectionaboveandshowninTable1.Wethereforeconsideritlikely ofthewesternlargecavity(features1and2).Thecentralaxisof
thatthehardexcessobservedinthegalaxymidplaneisreal. theextendedwesternarmofthe330-MHzradioemissionspatially
coincideswiththeprojectedcentreofthehotarcstructure,justas
itdoesthewesterncavity.
3.6 Radialprofilesofgasproperties As can be seen by comparing the temperature map with the D
o
Weobtainradialprofilesoftemperature,density,pressureanden- overlaid X-ray surface brightness contours (right panel), the 10- wn
tropybyextractingspectrafrombothObsIDs7329and6934usinga arcsec(∼15kpc) coldfilamentisnearlycospatialwiththebright loa
d
seriesof20concentriccircularannuliwitha1.5-arcsecinnerradius, X-ray filament seen in Fig. 1. In the hardness analysis presented ed
3.6-arcsecstackingincrementand74-arcsecouterradius.Weighted inSection3.5,weshowthatthisbrightfilamentisassociatedwith fro
m
responsematricesweregenerated,andthebackground-subtracted anX-raysoftexcess(seeFig.5).Thereisslightspatialmismatch h
aspbesoctrrbaefdroMmEeKaAchLamnnoudleulss(waserbeefifottreed,Nsim,uZltaanndeozuwselyreinfroXzSePEnCtowtihthe bbientwnienegnanthdesmfeoatoutrheisn,gbpurtocthesisseissunnodterstuarkpernisdinugringgivcerneatthioensopfattihael ttp://m
H n
appropriatevalues).Theextractedspectraareanemission-weighted maps. Inevitably, this results in some loss of spatial information ra
s
superpositionofpropertiesalongthelineofsightextendingthrough onatleastthescaleofthecontourbinsizes.Butwhenconsidered .o
x
a3Ddistributionofthermalplasma.Projectioneffectsaretherefore together,Figs5and7clearlyshowthatfeature5inFig.2isa‘cold’ fo
rd
important;however,typical‘onionskin’spectraldeprojectiontech- filament. jo
u
niquesarenotappropriateinthiscaseastheinner100kpcofX-ray InFig.9weshowthepseudo-entropy,3 pseudo-pressure,metal rn
a
emissionshowsverylargedeparturesfromsphericalsymmetry.We abundance and hardness ratio maps. We overlay 330-MHz and ls.o
thereforechoosetoshowonlyprojectedspectralprofiles.2 1.3-GHz contours on the pseudo-entropy map (top left panel) in rg
In Fig. 6 (top to bottom) we show the projected temperature, blackandwhite,respectively.330-MHz,1.3-GHzand8.4-GHzcon- at U/
electrondensity,pressureandentropyprofiles(respectively)outto tours are shown on the pseudo-pressure map (top right) in black, n
100kpc.ThelatterthreequantitiesarederivedfromtheMEKAL green and white, respectively. We intentionally show fewer 330- ive
rs
normalization (emission measure) using the equations listed in MHzcontoursonthepseudo-entropymaptoallowthehotarcfea- ity
the Fig. 6 caption, as well as a simple volume assumption. See turetobeclearlyvisible.Oneachmap,thelocationofthehotarc of K
Tremblay (2011) for more detail on how these profiles were ob- featureseenintheX-raytemperaturemapismarked.Bothpseudo- e
n
tained.WemarkthelocationoftheX-raycavitynetworkoneach entropyandpseudo-pressureareelevatedinthehotarcregion.This tu
c
profile,andnoteamarginalsteepeningofthetemperaturegradient resultwillbediscussedinmoredetailinSection6. ky
L
withinthisregion.Allofourprofilesareconsistentwithpaststudies InthebottomleftpanelofFig.9weshowthemetalabundance ib
o9f22b;oMthctNheameaarrlaye1t8a-l.k2s0(0g1o;oCdatvimagen)oCloheatnadlr.a20o0b9se)ravnadtiothne(XOMbsMID– mabaupn.dKanirckepaintriAck2,5M97cNinammaorrae&deCtaaivlatghnaonlow(e20w1i1ll)dsotudhieerde.mTehtaalt raries o
Newton observation of A2597 (Morris & Fabian 2005). We plot work found higher abundance gas extended along the cavity and n A
independentconsistencychecksonourdensityandentropyprofiles radioaxisinA2597,andsuggestedthatthiscouldbeevidencefora ug
u
byusingourBetamodelfittedtothesurfacebrightnessprofileand metal-enrichedoutflowdrivenbytheradiosource.Sucharesultis st 2
theentropyparametrizationfromCavagnoloetal.(2009),respec- consistentwithpredictionsfromtheoreticalAGNfeedbackmodels 0
tively.Thestarformationthresholdmarkedontheentropyprofile (e.g. Pope et al. 2010; Gaspari, Ruszkowski & Sharma 2012), as , 20
1
isdiscussedinTremblayetal.(2012). wellasresultsfromotherCCclusters(e.g.HydraA;Simionescu 4
etal.2009;Gittietal.2011).Ourabundancemaphasbeenmade
withlargespatialbinsusingaS/N=70threshold,asnotedprevi-
4 X-RAY SPECTRAL MAPS ously.Thisresultsinlossofspatialinformationonthescaleofthe
In the left-hand panel of Fig. 7 we present the projected X-ray coldfilamentandhotarc,thoughwedonotethathigherabundance
temperaturemap.330-MHz,1.3-GHzand8.4-GHzradiocontours gasisgenerallyextendedalongthecavityandradioaxis,consis-
areoverlaidinblack,greenandwhite,respectively.Theright-hand tent with the results from Kirkpatrick et al. (2011). Higher-than-
panel shows the same map, smoothed with an adaptive Gaussian average abundance is not observed at the location of the western
kernelasaviewingaid.WeoverplottheadaptivelysmoothedX-ray largecavity(markedwiththewhitearrow),butitisseenalongits
surfacebrightnesscontoursinblack.Thecolourmapencodesthe edges.Thismightbeexpectedifthemetal-enrichedgaswaspushed
best-fitting MEKAL gas temperature (kT) using the scale shown
at the right of the figure. Both panels are aligned and share the
3Weusetheterm‘pseudo’becausethesquarerootoftheemissionmeasure
(i.e. the MEKAL normalization) is used as a proxy for the gas density.
2Asatest,wedidattemptsphericaldeprojection,andtheresultswerevery No inherently uncertain volume assumption is made, so this cannot be
similartoourprojectedprofiles. consideredtheactualgasdensity.
(cid:2)C 2012TheAuthors,MNRAS424,1026–1041
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