Residual cooling and persistent star formation amid active galactic nucleus feedback in Abell 2597

20 Pages·2014·12.93 MB·English

Durham Research Online
Deposited in DRO:
26 November 2013
Version of attached (cid:28)le:
Published Version
Peer-review status of attached (cid:28)le:
Peer-reviewed
Citation for published item:
Tremblay, G. R. and O’Dea, C. P. and Baum, S. A. and Clarke, T. E. and Sarazin, C. L. and Bregman, J. N.
and Combes, F. and Donahue, M. and Edge, A. C. and Fabian, A. C. and Ferland, G. J. and McNamara, B.
R. and Mittal, R. and Oonk, J. B. R. and Quillen, A. C. and Russell, H. R. and Sanders, J. S. and Salom(cid:1)e, P.
and Voit, G. M. and Wilman, R. J. and Wise, M. W. (2012) ’Residual cooling and persistent star formation
amid active galactic nucleus feedback in Abell 2597.’, Monthly notices of the Royal Astronomical Society., 424
(2). 1042-1060 .
Further information on publisher’s website:
http://dx.doi.org/10.1111/j.1365-2966.2012.21278.x
Publisher’s copyright statement:
This article has been published in the Monthly Notices of the Royal Astronomical Society (cid:13)c 2012 The Authors.
Published by Oxford University Press on behalf of The Royal Astronomical Society. All rights reserved.
Additional information:
Use policy
Thefull-textmaybeusedand/orreproduced,andgiventothirdpartiesinanyformatormedium,withoutpriorpermissionorcharge,for
personalresearchorstudy,educational,ornot-for-pro(cid:28)tpurposesprovidedthat:
• afullbibliographicreferenceismadetotheoriginalsource
• alinkismadetothemetadatarecordinDRO
• thefull-textisnotchangedinanyway
Thefull-textmustnotbesoldinanyformatormediumwithouttheformalpermissionofthecopyrightholders.
PleaseconsultthefullDROpolicyforfurtherdetails.
DurhamUniversityLibrary,StocktonRoad,DurhamDH13LY,UnitedKingdom
Tel:[phone]|Fax:[phone]
https://dro.dur.ac.uk
Mon.Not.R.Astron.Soc.424,1042–1060(2012) doi:10.1111/j.1365-2966.2012.21278.x
Residual cooling and persistent star formation amid 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 D
3ChesterF.CarlsonCenterforImagingScience,54LombMemorialDrive,Rochester,NY14623,USA ow
4Harvard–SmithsonianCenterforAstrophysics,60GardenStreet,Cambridge,MA02138,USA nlo
5RadcliffeInstituteforAdvancedStudy,10GardenStreet,Cambridge,MA02138,USA ad
e
67NDaepvaalrtRmeesnetarocfhALstarboonroamtoyr,yURneivmeorsteitySeonfsVinirggiDniiavi,sPioOn,BCooxd4e070231235,4C55h5arOlovteterslovoilkleA,vVeAnu2e29S0W4,-4W3a2s5h,inUgStAon,DC20375,USA d from
8DepartmentofAstronomy,UniversityofMichigan,AnnArbor,MI48109,USA h
9ObservatoiredeParis,LERMA,CNRS,61Av.del’Observatoire,75014Paris,France ttp
10PhysicsandAstronomyDepartment,MichiganStateUniversity,EastLansing,MI48824-2320,USA ://m
11DepartmentofPhysics,DurhamUniversity,DurhamDH13LE nra
12InstituteofAstronomy,MadingleyRoad,CambridgeCB30HA s.o
13DepartmentofPhysics,UniversityofKentucky,Lexington,KY40506,USA xfo
14PhysicsandAstronomyDepartment,WaterlooUniversity,200UniversityAvenueW.,Waterloo,ONN2L2G1,Canada rd
jo
15ASTRON,NetherlandsInstituteforRadioAstronomy,POBox2,7990AADwingeloo,theNetherlands u
16DepartmentofPhysicsandAstronomy,UniversityofRochester,Rochester,NY14627,USA rna
ls
.o
rg
a/
Accepted2012May9.Received2012May8;inoriginalform2012March1 t D
u
rh
a
m
U
ABSTRACT n
iv
NewChandraX-rayandHerschelFar-Infrared(FIR)observationsenableamultiwavelength ers
studyofactivegalacticnucleus(AGN)heatingandintraclustermedium(ICM)coolinginthe ity
L
brightest cluster galaxy (BCG) of Abell 2597 (z = 0.0821). The new Chandra observations ib
ra
revealthecentral(cid:2)30kpcX-raycavitynetworktobemoreextensivethanpreviouslythought, ry
o
andassociatedwithenoughenthalpytotheoreticallyinhibittheinferredclassicalcoolingflow. n N
Nevertheless, we present new evidence, consistent with previous results, that a moderately ov
e
m
strongresidualcoolingflowispersistingat4–8percentoftheclassicallypredictedratesina b
e
spatiallystructuredmanneramidthefeedback-drivenexcavationoftheX-raycavitynetwork. r 2
6
New Herschel observations are used to estimate warm and cold dust masses, a lower limit , 2
0
gas-to-dust ratio and a star formation rate consistent with previous measurements. [OI] and 13
CO(2−1)lineprofilesareusedtoconstrainthekinematicsofthe∼109M(cid:3) reservoirofcold
molecular gas. The cooling time profile of the ambient X-ray atmosphere is used to map
the locations of the observational star formation entropy threshold as well as the theoretical
thermal instability threshold. Both lie just outside the (cid:2)30-kpc central region permeated by
X-raycavities,andstarformationaswellasionizedandmoleculargaslieinteriortoboth.The
youngstarsaredistributedinanelongatedregionthatisalignedwiththeradiolobes,andtheir
estimatedagesarebothyoungerandolderthantheX-raycavitynetwork,suggestingbothjet-
triggeredaswellaspersistentstarformationoverthecurrentAGNfeedbackepisode.Bright
(cid:2)E-mail:[email protected]
(cid:4)C 2012TheAuthors
MonthlyNoticesoftheRoyalAstronomicalSociety(cid:4)C 2012RAS
ResidualcoolingamidAGNfeedbackinA2597 1043
X-ray knots that are coincident with extended Lyα and far-ultraviolet continuum filaments
motivateadiscussionofstructuredcoolingfromtheambienthotatmospherealongaprojected
axisthatisperpendiculartoX-raycavityandradioaxis.WeconcludethatthecoolingICMis
thedominantcontributorofthecoldgasreservoirfuellingstarformationandAGNactivityin
theAbell2597BCG.
Keywords: galaxies:active–galaxies:clusters:general–galaxies:clusters:individual:Abell
2597–galaxies:clusters:intraclustermedium–galaxies:starformation.
thethermalgas,whichthenbuoyantlyrise,entrainmagneticfields
1 INTRODUCTION
andcolderinterstellarmedium(ISM)phases,andlocallythermalize
For a subset of galaxy clusters with sharply peaked X-ray sur- enthalpyassociatedwiththeirinflationasambientgasmovestorefill
facebrightnessprofiles,theintraclustermedium(ICM;e.g.Sarazin theirwakes(e.g.Begelman2001;Churazovetal.2002;Reynolds,
1986)cancoolviabremsstrahlungprocessesfrom>107to(cid:5)104K Heinz&Begelman2002;Ruszkowski&Begelman2002;Fabian
D
ontime-scalesmuchshorterthanaGyrwithinaradiusof∼100kpc. 2003;Bˆırzanetal.2004;Robinsonetal.2004;Dursi&Pfrommer ow
Simplemodelspredictthatrunawayentropylossbygaswithinthis 2008;Fabianetal.2008;Gittietal.2011).Thephenomenonislikely nlo
a
radius accompanies subsonic, nearly isobaric compression by the episodicataratecoupledtotheAGNdutycycle,andtotalenergy d
e
atomtbhieenctehnotrtarlebserirgvhotier,stdrcilvuisntgeraglaolnagx-yliv(heedrcelaafstesircBalCcGoo;lsienegcflooowlinogn itnop1u0t6w1ehregn.sIunmprminecdipolvee,rththiseicsleunstoeurglhifetotimreeplceannisrhanthgeetforotamle∼ne1r0g5y5 d from
flow reviews by Fabian 1994; Peterson & Fabian 2006). In these budget of ICM radiative losses for an average of the CC cluster http
‘schoooulldcodrreiv’e(eCxCtr)emcleussttearrsf,ocrmataastitoronprhaitcesc(o1n0d2e–n1s0a3tiMon(cid:3)oyfrt−h1e)aImCMid pthoipsuelanteirogny,aislthoonueghofthseevsepraatliailmdpisotrrtiabnuttiopnroabnledmthsetrhmaatliczhaatliloenngoef ://mn
massive cold gas reservoirs (∼1012M(cid:3)) in the BCG, and high- the model(e.g. McNamara&Nulsen2007, 2012,and references ras
.o
resolution X-ray spectroscopy should detect bright coolant lines therein). The physics coupling AGN mechanical energy to ICM x
stemmingfrom(cid:2)103M(cid:3) cascadesofmultiphasegascondensing entropy remain poorly understood, and thermal conduction, gas ford
from the hot atmosphere. Yet three decades of searches for these sloshing and dynamical friction likely play additional important jou
rn
expectedcoolingflowmasssinksreturnedwithresultsthatwereor- roles (e.g. Sparks, Macchetto & Golombek 1989; Ruszkowski & a
ls
dersofmagnitudebelowpredictions,consistentonlywithresidual Begelman 2002; Voigt et al. 2002; Brighenti & Mathews 2003; .o
coolingat∼1–10percentoftheexpectedrates(e.g.Allen1969, El-Zant, Kim & Kamionkowski 2004; Soker, Blanton & Sarazin arg/
1995;DeYoung&Roberts1974;Baan,Haschick&Burke1978; 2004; Voigt & Fabian 2004; Sparks et al. 2009; Morsony et al. t D
u
Haynes,Brown&Roberts1978;Peterson1978;Shostaketal.1980; 2010; Parrish, Quataert & Sharma 2010; ZuHone, Markevitch & rh
a
O’Dea&Baum1987,1997;McNamara&O’Connell1989;O’Dea Johnson2010;Blantonetal.2011;Sparksetal.2012). m
U
et al. 1994a; O’Dea, Payne & Kocevski 1998; Peres et al. 1998; n
Mittazetal.2001;Petersonetal.2001,2003;Tamuraetal.2001; ive
Sakelliouetal.2002;Xuetal.2002;Edge&Frayer2003;Bregman 1.1 ResidualcoolingandstarformationamidAGNfeedback rsity
&Lloyd-Davies2006;Sandersetal.2008). Criticaldetailsoftheheatingandcoolingfeedbackloopareencoded L
ib
AttemptstoreconciletheseresultswiththehighX-rayluminosi- inthemass,energyandtime-scalebudgetsofthelow-temperature, ra
tiesandlonglifetimesassociatedwiththeCCphasehaveinvoked high-densitygasphasespreferentiallyfoundinCCBCGs,suchas ry o
non-gravitationalheatingmechanismstoinhibitorreplenishanav- filamentaryforbiddenandBalmeremission-linenebulaeand∼109– n N
erage∼90percentofICMradiativelossesovertheclusterlifetime 1010M(cid:3)reservoirsofbothvibrationallyexcitedandcold1molec- ov
e
(e.g.reviewbyPeterson&Fabian2006).Onepromisingcandidate ular gas (e.g. Hu, Cowie & Wang 1985; Baum 1987; Heckman m
b
forquenchingcoolingflowsintheinnermostregionsofcoolcores etal.1989;Jaffe&Bremer1997;Donahueetal.2000;Edge2001; er 2
isafeedbackloopregulatedbythemechanicaldissipationofactive Jaffe, Bremer & van der Werf 2001; Edge et al. 2002; Wilman 6, 2
galacticnucleus(AGN)power(e.g.Rosner&Tucker1989;Baum et al. 2002; McNamara, Wise & Murray 2004; Jaffe, Bremer & 0
1
3
&O’Dea1991;Churazovetal.2002;Bˆırzanetal.2004;Dunn& Baker2005;Egamietal.2006;Raffertyetal.2006;Salome´ etal.
Fabian2006;Raffertyetal.2006;Bestetal.2007;Edwardsetal. 2006,2011;Wilman,Edge&Swinbank2009;Edgeetal.2010a,b;
2007; Mittal et al. 2009, reviews by McNamara & Nulsen 2007, Oonketal.2010;Mittaletal.2011;Wilmanetal.2011;Limetal.
2012;Fabian2012).Theparadigmissupportedbystrongcircum- 2012).
stantialevidence,includingobservationsofkiloparsec(kpc)scale While residual ICM condensation can contribute a major frac-
X-raycavitiesinspatialcorrelationwithradioemissionassociated tion of the mass budget for these phenomena (e.g. Baum 1987;
withAGNoutflows(Bo¨hringeretal.1993;Fabianetal.2000,2006; Heckmanetal.1989;Cavagnoloetal.2008;Quillenetal.2008;
McNamaraetal.2000,2001;Blantonetal.2001;Churazovetal. Rafferty, McNamara & Nulsen 2008; O’Dea et al. 2008; Hudson
2001;Bˆırzanetal.2004;Formanetal.2005,2007;Nulsenetal. et al. 2010; McDonald et al. 2010, 2011), their tempera-
2005).Thepoweroftheseradiosourcesarestatisticallycorrelated tures and ionization states are often inconsistent with the
withX-rayluminosityfromwithinthecoolingradius,andthemost
radio-loud BCGs are ubiquitously associated with the strongest
1Throughoutthispaper,wewilluse‘hot’todescribe107<T<108K(X-
coolcores(e.g.Burns1990;Bˆırzanetal.2004;Raffertyetal.2006;
raybright)ICM/ISMphases,‘warm’todescribe104(cid:2)T<105K[optical
Mittaletal.2009;Sun2009;Hudsonetal.2010). andultraviolet(UV)bright]components,and‘cold’todescribe10(cid:2)T(cid:2)
Observationallysupportedsimulationsshowthattheoutflowing 104K[N/M/far-infrared(FIR)bright]components.Wewillnotdiscussthe
plasmacandrivesoundwavesandsubsonicallyexcavatecavitiesin criticallyimportant105–107Kregimeatgreatlengthinthispaper.
(cid:4)C 2012TheAuthors,MNRAS424,1042–1060
MonthlyNoticesoftheRoyalAstronomicalSociety(cid:4)C 2012RAS
1044 G.R.Tremblayetal.
10 (cid:2) T (cid:2) 104K phases of a purely radiative cooling flow (e.g. &Donahue1997).Thegalaxyishosttooneofthenearestknown
Donahue & Voit 1991; Voit & Donahue 1997). Thermal conduc- compact steep spectrum (CSS; O’Dea 1998) radio sources, PKS
tionandsuprathermalelectronheatingnowappearstobeimportant 2322−122,whichexhibitsacompact(10kpc)andbentFanaroff–
(Ferland et al. 2008, 2009; Sparks et al. 2009, 2012; Donahue Riley class I (FR I) morphology at 8.4 GHz (Fanaroff & Riley
et al. 2011; Fabian et al. 2011; Mittal et al. 2011; Oonk 2011; 1974; Wright & Otrupcek 1990; Griffith & Wright 1994; O’Dea
Johnstone et al. 2012), and a critical role is played by the etal.1994a;Sarazinetal.1995).
clumpy and filamentary distributions of star formation ongoing A2597 is one of the only CC clusters with a convincing Far
amid these cold reservoirs on (cid:2) 30kpc scales (e.g. Johnstone, Ultraviolet Spectroscopic Explorer (FUSE) detection of
Fabian&Nulsen1987;Romanishin1987;McNamara&O’Connell [OVI]λ1032 Å emission stemming from a 105−107K gas
1989; Hu 1992; Crawford & Fabian 1993; Allen 1995; Hansen, component (Oegerle et al. 2001), and high-resolution XMM–
Jorgensen&Norgaard-Nielsen1995;Smithetal.1997;Voit&Don- Newton X-ray spectroscopy reveals weak FeXVII features amid
ahue1997;Cardiel,Gorgas&Arago´n-Salamanca1998;Hutchings a soft X-ray excess (Morris & Fabian 2005). It is therefore
&Balogh2000;Mittazetal.2001;Oegerleetal.2001;O’Deaetal. one of the best known candidates for harbouring a moderately
2001,2004,2008,2010;McNamara,Wise&Murray2004;Hicks powerfulresidualcoolingflowwithamassdepositionrateof90±
&Mushotzky2005;Raffertyetal.2006,2008;Bildfelletal.2008; 15M(cid:3) yr−1 within a 100-kpc cluster-centric radius (Morris &
Voitetal.2008;Loubseretal.2009;McDonaldetal.2010,2011; Fabian 2005). The BCG harbours a 1.8 ± 0.3 × 109M(cid:3) cold D
Oonketal.2011). H2 component, inferred from CO observations2 (e.g. Edge 2001; ow
n
Estimated star formation rates range from a few to tens of so- Salome´ & Combes 2003), as well as a young stellar component lo
a
lar masses per year, and strongly correlate with upper limits on cospatialwithanHα-brightfilamentaryemission-linenebula(e.g. de
d
spectroscopically derived ICM mass deposition rates, as well as Heckman et al. 1989; Voit & Donahue 1997; Koekemoer et al. fro
CO-inferred molecular gas masses (e.g. O’Dea et al. 2008). This 1999;O’Deaetal.2004;Oonketal.2011).Thesefeaturesreside m
suggestsadirectcausalconnectionbetweenreducedcoolingflows amid a network of prominent X-ray cavities (McNamara et al. http
and star formation, as BCGs with young stellar populations are 2001; Clarke et al. 2005), making A2597 an ideal subject for ://m
always found in CC clusters (Bildfell et al. 2008; Loubser et al. studiesofAGN/ISMinteractions(Tremblayetal.2012).Forthese n
ra
2009).Newevidencesuggeststhatstarformationoccurswhenmul- reasonsandothers,A2597enjoysalonghistoryofcross-spectrum s.o
tiphasecloudsandfilamentsprecipitateoutoftheICMasitscentral analysis in the literature (X-ray – Crawford et al. 1989; Sarazin xfo
entropydropsbelowacriticalthreshold((cid:2)20–30keVcm−2;Cav- et al. 1995; Sarazin & McNamara 1997; McNamara et al. 2001; rd
jo
agnolo etal. 2008; Raffertyetal. 2008; Voit et al. 2008; Sharma Clarkeetal.2005;Morris&Fabian2005;UV/optical–McNamara urn
etal.2011;Gaspari,Ruszkowski&Sharma2012). &O’Connell1993;DeYoung1995;Voit&Donahue1997;Cardiel als
Butwhilethepathwayofentropylossfromhotambientmedium etal.1998;Koekemoeretal.1999;McNamaraetal.1999;Oegerle .org
to cold star-forming clouds may be strongly influenced by AGN etal.2001;O’Deaetal.2004;Jaffeetal.2005;Oonketal.2010, a/
feedback,itisnotknownwhetherresidualcoolingpersistsatcon- 2011;IR–McNamara&O’Connell1993;Voit&Donahue1997; t D
u
stantlowlevelsorinelevatedepisodesanti-correlatedtotheAGN Koekemoeretal.1999;McNamaraetal.1999;O’Deaetal.2004; rh
a
duty cycle (e.g. O’Dea et al. 2010; Tremblay 2011). Moreover, Jaffeetal.2005;Donahueetal.2007,2011;sub-mm–Edge2001; m
U
modelsinvokingradio-modefeedbacktoquenchcoolingflowsig- Salome´ & Combes 2003; Edge et al. 2010a,b; radio – O’Dea, n
iv
natures such as star formation must be reconciled with evidence Baum&Gallimore1994b;Sarazinetal.1995;Tayloretal.1999; e
rs
that in several systems (e.g. Abell 1795 and Abell 2597; O’Dea Pollack,Taylor&Allen2005;Clarkeetal.2005). ity
et al. 2004), the propagating radio source may trigger compact, InSection2wedescribethenewandarchivalmultiwavelength Lib
short-duration starbursts as it propagates amid a dense medium observationsusedinthispaper.InSection3weusethenewChandra ra
ry
(e.g. Elmegreen & Elmegreen 1978; Voit 1988; De Young 1989; X-ray observations to assemble an AGN feedback energy budget o
n
McNamara&O’Connell1993;O’Deaetal.2004;Batcheldoretal. byusingthekpc-scalecavitynetworkasalowerlimitcalorimeter N
o
2007; Holt, Tadhunter & Morganti 2008; Holt et al. 2011). The to the AGN kinetic energy input. In Section 4 we present new v
e
m
picture is further complicated by the role played by (e.g.) ther- HerschelFIRdataandusethemtoplaceconstraintsontheresidual b
e
malconductionandcoldaccretionscenarioslikegas-richmergers, coolingflow.Theseresultsareusedtoframeadiscussiononstar r 2
whoseimportancerelativetoresidualhot-modeICMcoolinghas formation,whichwepresentinSection5.Aconcludingdiscussion 6, 2
drivenadebatethatisstillunsettledafterthreedecades(e.g.Sparks and summary are provided in Sections 6 and 7. Throughout this 01
etal.1989,2012;Holtzmanetal.1996).Advancesinunderstanding work,weadoptH0=71h−711kms−1Mpc−1,(cid:5)M=0.27and(cid:5)(cid:6)= 3
largelyrelyuponmultiwavelengthdatathatsamplealltemperature 0.73. In this cosmology, 1arcsec corresponds to ∼1.5kpc at the
phases of the ISM in CC BCGs, the transport processes between redshiftoftheA2597BCG(z=0.0821).Thisredshiftcorresponds
thesephases,andtheirassociatedmassandenergybudgets. to an angular size distance of DA ≈ 315Mpc and a luminosity
distanceofD ≈369Mpc.
L
1.2 ThebrightestclustergalaxyinAbell2597
2 OBSERVATIONS AND DATA REDUCTION
Tothatend,inthispaperwepresentamultiwavelengthstudyofthe
Table 1 contains a summary of all new and archival observations
archetypalCCclusterAbell2597.NewChandraX-rayandHer-
usedinthispaper.Wereferthereadertothepublicationslistedin
schelFIRobservations,combinedwithavastsuiteofarchivaldata,
column 9 for technical information pertaining to the archival ob-
enablearadio-through-X-raystudyoftheICM/ISMonthescaleof
servations.ThenewChandraX-rayobservations,totalling150ks
itsAGNfeedbackinteractionregion(i.e.itscentral(cid:2)30kpcX-ray
cavitynetwork).Abell2597(hereafterA2597)isanAbell(Abell
1958;Abell,Corwin&Olowin1989)richnessclass0galaxycluster 2UpdatedCO-inferredmolecularhydrogenmassisfromP.Salome´(private
withanX-raysurfacebrightnessprofilethatissharplypeakedabout communication), using unpublished IRAM (Institut de Radioastronomie
itscentrallydominantellipticalBCGatredshiftz=0.0821(Voit Millime´trique)observations.WediscussthisinSection4.
(cid:4)C 2012TheAuthors,MNRAS424,1042–1060
MonthlyNoticesoftheRoyalAstronomicalSociety(cid:4)C 2012RAS
ResidualcoolingamidAGNfeedbackinA2597 1045
Table1. Asummaryofthenewandarchivalobservationsused(directlyorreferentially)inthisanalysis.Thistablealsoappliestotheanalysispresented
inTremblayetal.2012.Column(1):facilityname;column(2):instrumentusedforobservation;column(3):configurationofinstrument/facility;column
(4):wavelengthregime/spectrallineobservedorfilterused;column(5):exposuretime;column(6):facility-specificobservationorprogrammeID;column
(7):dateofobservation;column(8):principalinvestigator(PI)ofobservationorprogramme;column(9):referencetopublicationwherethedatawerefirst
published–1:McNamaraetal.(2001);2:Oonketal.(2011);3:O’Deaetal.(2004);4:Koekemoeretal.(1999);5:Holtzmanetal.(1996);6:Donahueetal.
(2000);7:Donketal.(2010);8:Donahueetal.(2007);9:Edgeetal.(2010a);10:Edgeetal.(2010b);11:Sarazinetal.(1995);12:Tayloretal.(1999);13:
Clarkeetal.(2005).New:datafirstpublishedinthispaper.
Observatory Instrument Mode/config. Band/filter/line Exp.time Prog./obs.ID Obs.date ProgrammePI Reference
(1) (2) (3) (4) (5) (6) (7) (8) (9)
X-rayobservations
Chandra ACIS-S FAINT X-ray(0.5−7keV) 39.8ks 922 2000Jul28 McNamara 1
··· ACIS-S VFAINT X-ray(0.5−7keV) 52.8ks 6934 2006May1 Clarke New
··· ACIS-S VFAINT X-ray(0.5−7keV) 60.9ks 7329 2006May4 Clarke New
Farultraviolet/optical/near-infraredobservations
HST ACS SBC F150LP(FUV) 8141s 11131 2008Jul21 Jaffe 2 D
o
··· STIS FUVMAMA F25SRF2(Lyα) 1000s 8107 2000Jul27 O’Dea 3 w
n
··· WFPC2 ··· F410M 2200s 6717 1996Jul27 O’Dea 4 lo
a
··· WFPC2 ··· F450W 2500s 6228 1995May07 Trauger 5 de
······ NWICFMPCO2S N·I·C·2 F702FW21(2RNband) 122100302ss 67242587 11999957MOacyt1097 DToranuagheure 65 d from
··· NICMOS NIC2 F160W(Hband) 384s 7457 1997Dec03 Donahue 6 h
ESOVLT SINFONI ··· Kband 600s 075.A-0074 2005Jul/Aug Jaffe 7 ttp://m
Mid-/far-infraredobservations n
Spitzer IRAC Mapping 3.6,4.5,5.8,8µm 3600s(each) 3506 2005Nov24 Sparks 8 ras.o
··· MIPS ··· 24,70,160µm 2160s(each) 3506 2005Jun18 Sparks 8 xfo
Herschel PACS Photometry 70,100,160µm 722s(each) 13421871(18-20) 2009Nov20 Edge 9 rd
··· SPIRE Photometry 250,350,500µm 3336s 1342187329 2009Nov30 Edge 9 jou
··· PACS Spectroscopy [OI]λ63.18µm 6902s 1342187124 2009Nov20 Edge 10 rna
··· ··· ··· [OIII]λ88.36µm 7890s 1342188703 2009Dec30 Edge 10 ls.o
········· ········· ········· [[O[CNIIBI]I]]λλλ111542751.7..5942µµµmmm 776332828472sss 111333444222111888878917420254 222000001990NDJaoenvc032400 EEEdddgggeee 111000 at Durg/
··· ··· ··· [SiI]λ68.47µm 11834s 1342210651 2010Dec01 Edge New rha
m
Radioobservations U
n
NRAOVLA ··· Aarray 8.44GHz 15min AR279 1992Nov30 Roettiger 11 iv
e
··· ··· Aarray 4.99GHz 95min BT024 1996Dec7 Taylor 12,13 rs
··· ··· Aarray 1.3GHz 323min BT024 1996Dec7 Taylor 12,13 ity L
··· ··· Aarray 330MHz 180min AC647 2003Aug18 Clarke 13 ib
··· ··· Barray 330MHz 138min AC647 2002Jun10 Clarke 13 rary
o
n
N
(128ks flare-free) in combined effective exposure time, were re- scopicresolution,isalsousedtoplaceconstraintsonthecoldgas ov
e
ducedusingthestandardCIAOv4.2threadswithv4.3.1ofthecal- kinematics. mb
ibration data base. More details can be found in Tremblay et al. er 2
(2012), which presents the spatial and spectral analysis of these 3 AGN FEEDBACK ENERGY BUDGET 6, 2
newobservations. 0
Kiloparsec-scaleX-raycavitiescanbeusedaslowerlimitcalorime- 13
Herschel Space Observatory observations of A2597 were ob-
tersonthekineticenergyassociatedwithAGNoutflows,andthe
tained in 2009 November with the Photodetector Array Camera
dutycycleover whichtheseoutburstsoccur(e.g. Churazovetal.
and Spectrometer (PACS), as well as the Spectral and Photomet-
2002;Bˆırzanetal.2004;Dunn&Fabian2006;Raffertyetal.2006;
ricImagingReceiver(SPIRE).Theseobservationswerepartofan
McNamara & Nulsen 2007, 2012; Fabian 2012). A study of the
OpenTimeKeyProject(OTKP)investigatingtheFIRlineandcon-
original40-ksChandraobservationbyMcNamaraetal.(2001)and
tinuumpropertiesofasampleof11BCGsinwell-knownX-rayand
Clarkeetal.(2005)(hereafterM01andC05,respectively)revealed
opticallineselectedCCclusters(PI:A.Edge,140h).Preliminary
westernandnorth-easternghostcavitiesinA2597.Thenew150-ks
resultsforA2597havebeenpublishedintheworkssubmittedas
Chandradatarevealthecavitynetworktobemoreextensivethan
partofthesciencedemonstrationphase(Edgeetal.2010a,b).The
originally thought, changing the interpretation of the AGN feed-
datawereprocessedwiththeHerschelInteractiveProcessingEn-
backenergybudgetandoutbursthistory.Wediscussthesetwonew
vironment(HIPE)packageversion7.1.0.SeeEdgeetal.(2010a,b),
resultsinthissection.
Mittaletal.(2011)andOonketal.(inpreparation)fordetailson
thedatareduction.ThepresentpaperusesPACSandSPIREdata
3.1 TheX-raycavitynetwork
tofillincriticalgapsintheFIRspectralenergydistribution(SED)
forA2597,enablingconstraintsondustmassesandtemperatures. In Fig. 1 we present the combined 150-ks 0.5–7keV X-ray data
The[OI]λ68.4µmPACSobservation,becauseitisathighspectro- fromTremblayetal.(2012).Allpanelsarealignedwithanidentical
(cid:4)C 2012TheAuthors,MNRAS424,1042–1060
MonthlyNoticesoftheRoyalAstronomicalSociety(cid:4)C 2012RAS
1046 G.R.Tremblayetal.
D
o
w
n
lo
a
d
e
d
fro
m
h
ttp
://m
n
ra
s
.o
x
fo
rd
jo
u
rn
a
ls
.o
rg
a/
t D
u
rh
a
m
U
n
iv
e
rs
ity
L
ib
ra
ry
o
n
N
o
v
e
m
b
e
r 2
Figure1. Topleft:exposure-corrected0.5–7keVimageofthethreemergedChandraobservations(seeTable1).Thedatahavebeensmoothedwithan 6, 2
adaptiveGaussiankernel.Blackcontoursareoverlaidtobettershowthespatiallyanisotropicnatureoftheemission.Theinnermostcontourmarksafluxof 0
4.6×10−7photonss−1cm−2pixel−1,andthecontoursmoveoutwardswithafluxdecrementof2.0×10−8photonss−1cm−2pixel−1.Topright:thesame 13
0.5–7keVX-raycontours(ingreen),overlaidonthebroad-bandHST/WFPC2F702W(R-band)exposureoftheA2597BCG(showninorange).Notethatthe
anisotropyoftheX-rayemissionislargelyconfinedtotheinnerregionsofthegalaxy.Bottomleft:unsharpmaskoftheX-raydata,madebysubtractionofa
20-arcsecGaussiansmoothedversionfromtheadaptivelysmoothedversion.330-MHzVLAcontourshavebeenoverlaidingreen,whilethe1.3-GHzradio
contoursareplottedinblue,andthe8.4-GHzradiocontoursappearinblack.bottomright:unsharpmaskmadebysubtractingthesame20-arcsecGaussian
smoothedversionoftheimagefroma5-arcsecGaussiansmoothedversion,thendividingbythesumofthetwoimages.Themajor(10σ excessordeficit)
morphologicalfeatureswhichwillbethesubjectoffurtherspatialanalysisinthispaperhavebeenlabelled1–6.Thecolourschemesofthetwobottompanels
showregionsofX-raysurfacebrightnessexcessinred/orange,whiledeficits(cavities)appearinblack.Allpanelsshareanidenticalfieldofview,centredat
RA=23h25m19s.75andDec.=−12◦07(cid:8)26(cid:8).(cid:8)9(J2000).
50×50arcsec2(75×75kpc2)fieldofview(FOV)centredonthe marksafluxof4.6×10−7photonss−1cm−2pixel−1,andthecon-
X-ray centroid at RA = 23h25m19s.75 and Dec. = −12◦07(cid:8)26(cid:8).(cid:8)9 toursmoveoutwardswithadecrementof2.0×10−8 photonss−1
(J2000).Eastisleftandnorthisup.Thetopleftpanelshowsthe cm−2pixel−1.
exposure-corrected,mergeddataadaptivelysmoothedwithavari- InthetoprightpanelofFig.1weoverlaytheadaptivelysmoothed
ablewidthGaussiankernelwhoseradiusself-adjuststomatchthe X-raycontoursontheHubbleSpaceTelescope(HST)WideField
localeventdensity.Blacksurfacebrightnesscontoursareoverlaid Planetary Camera 2 (WFPC2) R-band observation of the A2597
tomakeindividualfeatureseasiertoview.Theinnermostcontour BCG(showninred/orange).NotethattheanisotropyoftheX-ray
(cid:4)C 2012TheAuthors,MNRAS424,1042–1060
MonthlyNoticesoftheRoyalAstronomicalSociety(cid:4)C 2012RAS
ResidualcoolingamidAGNfeedbackinA2597 1047
emissionisconfinedtothescaleoftheBCG,whiletheoutermost cluster-centricradiusR,thenthissonicrisetime-scaleisgivenby
regionsassumeasmoother,moreellipticalshape.Themajoraxes
oftheX-rayandBCGstellarisophotesarealigned. tcs (cid:9)R/cs. (1)
InthebottomtwopanelsofFig.1weshowthesame0.5–7keV
Astheinitialstagesofcavityinflationarethoughttobesupersonic,
dataprocessedintwoways:(1)ahighlyprocessedunsharpmask
followedbysubsonicbuoyantrise,thissimpleapproachmaybest
made by subtracting a 30-arcsec Gaussian smoothed image from
reflectanaverageofthetwophases.Alternatively,ifthesupersonic
theadaptivelysmoothedimageshowninFig.1(topleft),and(2)a
inflationperiodisanegligiblefractionofthecavity’sageanddrag
moreconventionalunsharpmaskmadebysubtractinga20-arcsec
forceslimitthecavity’sterminalvelocityv,thebuoyanttime-scale
Gaussian smoothed image from a 5-arcsec (non-adaptive) Gaus- t
canbewrittenas
siansmoothedversion.Thesubtracteddataarethendividedbythe
(cid:3)
sum of the two images. Regions of X-ray surface brightness ex-
R AC
cessoverthesubtractedsmoothbackgroundappearinwhite,while tbuoy (cid:9) v (cid:9)R 2gV, (2)
deficits(cavities)appearinblack.8.4-GHz,1.3-GHzand330-MHz t
VeryLargeArray(VLA)radiocontoursfromSarazinetal.(1995),
wheregisthelocalgravitationalacceleration,V isthecavityvol-
Tayloretal.(1999)andC05areoverlaidonthebottomleftpanel. ume,Aisitscross-sectionalareaandC=0.75isthedragcoefficient
See section 3.2 of Tremblay et al. (2012) for a discussion of the adoptedfromChurazovetal.(2001)bye.g.Bˆırzanetal.(2004). D
strongradio/X-rayspatialcorrelationsthatareevidentinthisfig- Finally,cavityagescanbeconstrainedbyestimatingthetimere- ow
n
ure.Wenotethattheseunsharpmaskedgeenhancementmethods quiredtorefillthevolumedisplacedbyabubbleofradiusr asit lo
a
(particularlymethod1)areinherentlynoisy,andintroduceartefacts risesaheightequaltoitsdiameter, de
d
thatcomplicateaquantitativemorphologicalanalysis.Thesignif- (cid:4) (cid:4) fro
icance of the observed features must therefore be estimated from r r m
theun-processeddata.Weshowthesemostlyasviewingaidsfor trefill(cid:9)2R GM(<R) =2 g, (3) http
tphreocXes-sraeydicmavagiteiessshdoiswcnushseerdeidnotnhoistssiegcntiifiocna.nWtlyeddioffenroitneatphpaatrethnet whereM(<R)isthemassenclosedwithinasphereofradiusR. ://mn
morphologyfromtheun-processedrawChandradatathatcanbe Bˆırzanetal.(2004)madeallthreeestimatesfortheNEandW ras.o
seeninfig.2ofTremblayetal.(2012). ghost cavities in A2597 (features 1 and 3 in Fig. 1, bottom right xfo
InthebottomrightpanelofFig.1welabelthesixfeaturesthatare panel), using the early short (40 ks) Chandra observation. So as rd
associatedwith(cid:3)10σdeficitsorexcessesrelativetothelocalmean. to provide an independent check of their results using the deeper jou
Thesignificanceofthesefeatureswasestimatedbycomparingun- X-ray data, we follow their procedure almost exactly, and repeat rnals
smoothed counts in like-sized regions at the same cluster-centric their calculations for the M01 ghost cavities, the western large .o
radius.Throughoutthispaperwerefertothesefeatureswithacom- cavity(features1and2),aswellasthenewlydetectedcavities(4) arg/
monlabelandname.Theseare:(1)the‘M01westernghostcavity’, and(6)(aslabelledinFig.1).LikeBˆırzanetal.(2004),weadopt t D
(2) the ‘C05 X-ray tunnel’, (3) the ‘M01 northern ghost cavity’, theA2597BCGstellarvelocitydispersionofσ ≈224±19kms−1 urh
(4) the ‘eastern ghost cavity’, (5) the ‘cold filament’ and (6) the fromSmith,Heckman&Illingworth(1990)inourcalculationof am
thelocalgravitationalaccelerationg: U
‘C05filamentbasecavity’.Forclarity,thesenamesandlabelswill n
iv
be used consistently throughout this paper. Feature (2), the ‘cold e
filament’,isdiscussedinsection5ofTremblayetal.(2012)inthe g(cid:9) 2σ2, (4) rsity
contextofAGN/ISMinteractionsandmultiphasegasdredge-upby R Lib
theradiosource. assumingthatthegalaxyisanisothermalsphere.InTremblayetal. ra
ry
While(for‘historical’reasons)welabelfeatures(1)and(2)in- (2012) we calculate a local value for g by estimating the total o
n
dependently,ourdeeperdatamakeitclearthatwesternghostcavity enclosedgravitatingmassfromaβ-modelfittedtotheX-raysur- N
o
describedbyM01andC05ispartofalarger‘teardrop’shapedcav- face profile. For this discussion however, it is sufficient to adopt v
e
ity ∼25kpc in projected length (C05 originally suggested this in the Bˆırzan et al. (2004) method for estimating g (the two meth- mb
e
theirdiscussionofan‘X-raytunnel’).Thischangestheinterpreta- ods turn out to be roughly consistent at the radius of the X-ray r 2
tionoftheAGNoutbursthistory(relativetotheconclusionsdrawn cavitynetworkanyway).UnlikeBˆırzanetal.(2004),weusekTin- 6, 2
inM01),whichwewilldiscussbelow.Soastoenablecomparison ferredfromthecavitypositionsontheX-raytemperaturemappre- 01
3
withpastpapers(e.g.M01;Bˆırzanetal.2004;Raffertyetal.2006) sentedinTremblayetal.(2012)tocalculatethesoundspeedinthe
thathavetreatedtheM01cavityasaseparatefeature,wemaintain X-raygas.Weusethe2Dtemperaturemapinlieuofthe1Dradial
independent labels (1 and 2) for the cavity and tunnel. We stress temperature profile because A2597 is azimuthally anisotropic in
thatthesefeaturesarepartofonelargercavity,whichwewilllabel X-ray temperature (not to mention surface brightness) on these
‘1+2’andcallthe‘westernlargecavity’fortheremainderofthis scales. Furthermore, in calculating the pV work associated with
paper. each cavity, we use the projected density profile to estimate the
pressurenkTatthecluster-centricradiusofeachcavity.
TheresultsofthesecalculationsaregiveninTable2.Ourfindings
3.2 AgedatingtheX-raycavities
areroughlyconsistentwiththoseofBˆırzanetal.(2004).Forexam-
We adopt the simple model used by Bˆırzan et al. (2004) and ple,inagedatingtheM01westernghostcavitywefindt ≈27Myr,
cs
Raffertyetal.(2006)inestimatingroughagesfortheX-raycavities, t ≈88Myrandt ≈66Myr,whileBˆırzanetal.(2004)find
buoy refill
assumingtheirdensityisverylowrelativetotheambientgasden- 26,66and86Myr,respectively.Noneoftheseestimatesaccounts
sity.Threetime-scalescanbeconsidered,themostsimpleofwhich forprojectioneffects,andallassumethatthebubblerisespurelyin
assumesthat(cid:2)thebubblerisesintheplaneoftheskyatthesound theplaneofthesky.Thisresultsinanunderestimationofthecavity
speed c (cid:9) kT/μm , where μ = 0.62 is the mean molecular agebygenerallylessthanafactorof2(Bˆırzanetal.2004;Rafferty
s p
weightinunitsoftheprotonmass,m .Ifthebubbleisatprojected etal.2006;McNamara&Nulsen2007).
p
(cid:4)C 2012TheAuthors,MNRAS424,1042–1060
MonthlyNoticesoftheRoyalAstronomicalSociety(cid:4)C 2012RAS
1048 G.R.Tremblayetal.
Table2. SpatialpropertiesandenergeticsoftheX-raycavities.Column(1):labelofmorphologicalfeaturethatcorrespondstothat
assignedinthelowerrightpanelofFig.1;column(2):namegiventothecorrespondingfeature;column(3):projectedradialdistance
(length)ofthefeaturefromtheradiocoretotheestimatedcentre(edge)ofthefeature;column(4):estimatedradiusofthefeature;
column(5):estimatedworkassociatedwithcavityassumingsubsonicinflation;column(6):ageofthecavityifitrisesatthelocalsound
speed;column(7):buoyant,subsoniccavityrisetime;column(8):timeneededtorefillthedisplacedcavityvolume;column(9):X-ray
cavitypower,assumingthecavityisfilledwithrelativisticplasma.SeeSection3formoredetailsonthesecalculations.
Label Name R(k(pDc)) (kprc) (×10p5V7erg) (×1tc0s7yr) (×t1bu0o7yyr) (×t1re0fi7llyr) (×104P2ceavrgs−1)
(1) (2) (3) (4) (5) (6) (7) (8) (9)
1+2 Western‘largecavity’ 9 9 35.9 1.0 1.4 5.6 170.6
3 M01northern‘ghost’cavity 21 6.6 7.0 2.7 6.1 7.3 16.5
4 Eastern‘ghost’cavity 35 3.6 0.79 3.8 17.8 6.9 1.05
6 Filamentbasecavity 9 2.3 0.30 1.1 2.7 2.8 1.73
D
energydensities(equipartition),asteepspectralindexof−2.7be- ow
3.3 Cavityheatingenergyreservoir n
tween 1.3 GHz and 330 MHz, and that the source is a uniform lo
a
Incolumn9ofTable2wecalculatethemeaninstantaneouspower prolate cylinder with a filling factor of unity. This model yields de
ofeachcavityPcav, tahemrminaimlpurmesseunreergoyf5m×ag1n0e−t1ic1dfiyenldcmst−re2n.gWthenoofte29thµaGteqaunidpaartintoionn- d from
Pcav= 4(cid:10)ptV(cid:11) , (5) maybealess-than-idealassumptioninthiscase(e.g.Fabianetal. http
where(cid:10)t(cid:11)istheaverageofthecavityageslistedincolumns6–8.We 2q0u0ir2e)d.tFoubrtehtetermr aosrsee,sdsetehpeerspmecutlrtaiblainndderxadoifothoebsseoruvracteioancsroasrsetrhee- ://mn
haveassumedthecavitiesarefilledwitharelativisticplasma,such westernlargecavity. ras
.o
thattheirenthalpycanbeapproximatedas4pV(e.g.McNamara& The lower end of the 330-MHz lifetime range quoted above xfo
Nulsen2007). (t (cid:3) 8 × 106yr) is significantly shorter than the estimated rd
330MHz jo
The total sum of all cavity thermal energies (pV)listedin col- buoyant rise time of the western large cavity it fills (see Table 2, u
umn5is4.4×1058erg.Thisservesasarough,lowerlimitestimate column7).Ifweassumethatthisistheactualageofthesource,and rnals
onthekineticenergyinjectedbytheAGNintotheambientX-ray furtherassumethattheestimatedageofthewesternlargecavityis .o
rg
gasduringthe(a)currentAGNepisodeorperhaps(b)duringthe roughlycorrect,thenwerequire(a)insiture-accelerationofelec- a/
pasttwoormoreepisodesofactivity.Thisisclosetotheinferredme- tronsinthecavityor(b)anewepisodeofactivitytofeedtheplasma t D
u
chanicalenergyofthecentral8.4-GHzradiosource,whichSarazin intoanalreadypre-establishedcavity(which,ifempty,shouldcol- rh
etal.(1995)estimatedtobe9×1057erg.Inprinciple,theroughly lapseonasound-crossingtime(cid:2)107yr).Aswewillelaborateupon am
U
estimatedmechanicalinputfromtheradiosourcecouldbecapable below,thereislittlesupportingevidencefavouringeitherofthese n
ofaccountingfortheenergybudgetinferredfromtheX-raycavi- scenarios. ive
rs
ties,ignoringtime-scalearguments.Whetherornotthesecavities A‘radiosourceyoungerthanthecavity’scenariocouldalsobe ity
havebeenproducedbyoneormoreAGNepisodesisthesubjectof possibleifadiabaticand/orinverseComptonlossesdominateover L
ib
thefollowingsection. thesynchrotronprocesses,whichwouldresultintheradiosource ra
ry
fading on a time-scale shorter than the synchrotron lifetime. The o
n
importanceoftheseprocessesrelativetosynchrotronlossesdepends N
3.4 TheAGNdutycycleandheatingtime-scalebudget o
ontheBfieldstrengthandunknowndetailsofhowtheradiosource v
e
m
Anetworkofmultiplecavitiesfoundatvaryingcluster-centricradii fillsthebubble.InverseComptonlossesbecomemoreefficientthan b
(aswefindinA2597)maybeproducedwithanepisodicallyvarying synchrotronlosseswhentheBfieldisextremelyweak(B <1µG; er 2
AGN,transitioningbetweeneither‘on’and‘off’orhighandlow e.g.Fabianetal.2002),andadiabaticlossesarenotlikelyalimiting 6, 2
modes.Cyclingtimesbetweenthetriggeringofradioactivity,the factorbecausethewesternlargecavityislikelyrisingatlessthan 01
3
onsetofquiescenceandthesubsequentre-ignitionofactivityare thesoundspeed(notetheabsenceofanydetectedfastshocksinthe
typicallyestimatedtobeoftheorderof107−108yringeneral(e.g. X-raydata;e.g.Tremblayetal.2012).Wethereforeconsiderthis
Parmaetal.1999;Bestetal.2005;Shabalaetal.2008;Tremblay scenariounlikely.
et al. 2010), and synchrotron losses limit radio source lifetimes The upper end of the minimum-energy synchrotron lifetime is
to ∼108yr, unless there has been re-acceleration of the electron t (cid:3) 5 × 107yr (which itself is merely a lower limit). The
330MHz
population. Alternatively, a steady-state AGN with a duty cycle 330-MHz radio source could therefore easily be roughly of the
near 100 per cent can also produce a series of discrete cavities sameageasthecavityitfills.Thisisthesimplestscenario,asitis
(rather like a fish tank aerator or a dripping faucet; e.g. Peterson assumedthatthepropagationoftheradiosourceamidtheX-raygas
& Fabian 2006; McNamara & Nulsen 2007). In this section we isthemechanismthatexcavatesthecavity.Eveniftheequipartition
attempttodistinguishbetweenthesetwopossibilities. and spectral index assumptions mean that this estimated lifetime
Basedonsynchrotronlosstime-scales,C05estimatedthemin- is wrong, pressure equilibrium between the radio source and the
imum energy, lower limit lifetime of the 330-MHz source (green ambienthotgascanbeassumedtoestimateaverysimilar∼107yr
contours in the bottom left panel of Fig. 1) to be in the range of minimumage(e.g.Fabianetal.2002).Consideringthehighuncer-
t (cid:3)8×106yr(ifthespectralindexissteepdownto10MHz) taintiesassociatedwithagedatingbothcavitiesandradiosources,
330MHz
tot (cid:3)5×107yr(ifthespectralindexflattensbeyond330 (nottomentionprojectioneffects),wesuggestthatthewesternlarge
330MHz
MHz). This model assumes equal cosmic ray and magnetic field cavitywascreatedbythecurrent,ongoingepisodeofAGNactivity.
(cid:4)C 2012TheAuthors,MNRAS424,1042–1060
MonthlyNoticesoftheRoyalAstronomicalSociety(cid:4)C 2012RAS
ResidualcoolingamidAGNfeedbackinA2597 1049
Considering the above, we cannot rule out the possibility that where T is the virial temperature of the cluster. Classical mass
vir
the AGN in A2597 is on nearly ∼100 per cent of the time. The deposition rates for A2597 range from ∼100 to 500M(cid:3)yr−1
oldestcavity(i.e.feature4,withanestimatedageof1.8×108yr) overarangeofcluster-centricradiusspanning∼30−100kpc(e.g.
mayindeedbeassociatedwithapreviousepochofAGNactivity, Allenetal.2001;McNamaraetal.2001;Morris&Fabian2005).
but it could also be a detached bubble excavated by the current Taking a cluster virial temperature of kT = 3.5keV, we find
vir
episode(theavailabledatadonotpermitustodiscriminatebetween that the corresponding range of cooling luminosity is roughly
thesepossibilities).Wenotethatthepositionangleofthe8.4-GHz L ≈ (1−4)×1044 erg s−1. The rough sum of mean instan-
cool
radio lobes is significantly offset from the western large cavity, taneouscavitypowers(seeSection3.3andcolumn9ofTable2)
330-MHz and 1.3-GHz radio source (Fig. 1), and the Very Long is P ≈ 2 × 1044 erg s−1, suggesting that, in principle, there is
cav
BaselineArray(VLBA)small-scale(∼50pc)jetaxis(Tayloretal. enoughenthalpyassociatedwiththecurrentcavitynetworktooffset
1999).Wefinditunlikelythattheoffsetisduetothe8.4-GHzsource thebulkofradiativelossesandeffectivelyquenchthecoolingflow.
beingassociatedwithapreviousepochofactivity,consideringits Thesameconclusionholdsifweestimatethepredictedcooling
steepspectrum(O’Deaetal.1994b;Clarkeetal.2005),estimated flowluminositydirectlyfromthenewChandradata,usinglower
minimum-energy age of >5 × 106yr (Sarazin et al. 1995), and limittemperaturesderivedfromspectralfits(i.e.theMKCFLOW
alignmentoftheVLBA(<50pc)and330-MHz(>25kpc)major model kT values in table 1 of Tremblay et al. 2012). This is a
low
axes (Tremblay et al. 2012). Several past studies have suggested rough,order-of-magnitudeassumptionwhichneglectsmanyimpor- D
thatthebendisduetotheinteractionoftheradiosourcewiththe tantconsiderationssuchashowthisenthalpymightbedissipated ow
n
ambientdensegaseousmedium,eitherbydeflectionorback-flow anddistributedintheambientgas.OurfindingthattheX-raycavities lo
a
alongpre-establishedpressuregradients(e.g.Sarazinetal.1995; areassociatedwithenoughenergytoinhibitthepredictedclassical de
d
Koekemoeretal.1999;O’Deaetal.2004;Clarkeetal.2005;Oonk coolingflowluminosityisconsistentwithpreviousresults(Bˆırzan fro
etal.2010). etal.2004;Dunn&Fabian2006). m
h
ttp
3.5 Blackholeaccretionrate ://m
n
4 NEW EVIDENCE SUPPORTING A RESIDUAL ra
If the AGN is indeed nearly steady state, the central black hole COOLING FLOW MODEL FOR A2597 s.ox
(BH) requires a stable supply of gas from the ambient accretion fo
reservoir.Assumingamass-to-energyconversionefficiencyof(cid:9)= Intheprevioussection,weestimatedthattheX-raycavitynetwork rdjo
0.1(Wiseetal.2007),andassumingthattheenergyassociatedwith is associated with enough enthalpy to (in principle) replenish a urn
theX-raycavitiesisprovidedbytheAGN,thesumofmeaninstan- significantfractionoftheradiativelossesassociatedwithaclassical als
taneouscavitypowers(Pcav)requiresatime-averagedBHaccretion coolingflow.However,thewarmandcoldgasphasesintheA2597 .org
rateof BCGstronglysuggestthatsomecoolingfromtheambientX-ray a/
M˙acc∼ P(cid:9)cca2v ∼0.003−0.03(cid:5)0(cid:9).1(cid:6)−1 M(cid:3)yr−1, (6) adtimscousspshtehriesphoasssmibailnitayghedereto. persist,evenamidAGNheating.We t Durha
m
wherecisthespeedoflight.UsingtheM −σ relation(Magor- U
BH n
rian et al. 1998; Ferrarese & Merritt 2000; Gebhardt et al. 2000) iv
e
wyiietlhdsthaeroKu-gbhanBdHhmosatssluemstiinmoastietyofan∼d3s×tel1la0r8vMel(cid:3)oc,iftoyrdwishpicehrsitohne 4.1 HowmightcoolingpersistamidAGNfeedback? rsity L
c(Rorarfefseprtoynedtinalg.2E0d0d6i)n.gTthoinssaucgcgreetsitosnthraattethewaocuclrdetbioen∼ra1te0,Mif(cid:3)steyard−y1, aArsemcoennstiisotneendtwinitSheactmioond1er,arteesluyltsstrfornogmreXsMidMua–lN(seowmtoentimanedsFcaUllSeEd ibrary
‘reduced’) cooling flow with a mass deposition rate of ∼30 ± o
isstronglysub-Eddington,consistentwithpastresultsevenforvery n
15M(cid:3)yr−1at∼30kpcto90±15M(cid:3)yr−1at∼100kpc(Oegerle N
powerful AGN (e.g. Hydra A; Wise et al. 2007). If the AGN is o
insteadstronglyvariableorepisodic,thengastransporttotheBH et al. 2001; Morris & Fabian 2005). The cooling luminosity as- vem
sociated with this residual cooling flow is L ≈ (0.3–1) × b
couldbenon-steadyandtheactualaccretionratecouldvary. Cool,Resid e
1044 ergs−1.Aswith15–30percentofCCBCGs(dependingon r 2
6
thesample;e.g.Salome´ etal.2006),theA2597BCGharboursa , 2
3.6 Thereisenoughenergytoquenchaclassicalcoolingflow substantial1.8±0.3×109M(cid:3)reservoirofcoldH (inferredfrom 01
2 3
COobservations)withinitscentral30kpc(Edge2001;Salome´ &
WecalculatetheclassicalX-rayderivedcoolingtimeforA2597,
Combes 2003; P. Salome´, private communication). If the bulk of
t ≡ 5nkT, (7) themassbudgetforthiscoldgasissuppliedbytheresidualcooling
cool 2n2(cid:6) flow(ratherthane.g.amerger),thenAGNfeedbackcannotestab-
where n and kT are respectively the gas density and temperature lishanimpassableentropyfloor,andsomecoolingto<100Kmust
profiles obtained by Tremblay et al. (2012), and (cid:6) is the T > bepermittedevenifthereisenoughenergyinprincipletoquench
0.02keVportionofthecoolingfunctionfromSutherland&Dopita theclassicalcoolingflow.Weconsiderfourpossibilities:
(1993),usingthegeneralizationfromTozzi&Norman(2001).
(i) LowlevelsofresidualcoolingpersistevenwhileAGNfeed-
We find that the cooling time at the (cid:2)30kpc outermost radius
backisheatingtheambientenvironment;
oftheX-raycavitynetworkis∼300Myr.Theinstantaneouscool-
(ii) coolingoccursinaspatiallystructuredmanner,awayfrom
ingluminosityassociatedwiththeuninhibitedcoolingflow(with
thoseregionswhicharebeinglocallyheatedbye.g.buoyantcavities
noheating)canbecalculatedfromtheclassicaluninhibitedmass
andsoundwaves;
depositionrateM˙ using
cool (iii) cooling occurs in episodes which correspond to the times
5M˙ whentheBHisinactive,ortransitioningbetweenactiveandinactive
L = coolkT , (8)
cool 2 μm vir statesorbetweenhighandlowmodes;
p
(cid:4)C 2012TheAuthors,MNRAS424,1042–1060
MonthlyNoticesoftheRoyalAstronomicalSociety(cid:4)C 2012RAS
1050 G.R.Tremblayetal.
(iv) thesubstantialcoldgasreservoirintheA2597BCGstems connectionbetweenthesewarm/coldphenomenaandresidualcon-
fromsomethingotherthanacoolingflow,i.e.oneormoregas-rich densation from the ICM, but the literature has so far not reached
mergers. consensusastotherelativeimportanceofgas-richmajorandminor
mergers in this relationship (e.g. Sparks et al. 2012). Koekemoer
Thesearenottheonlypossibilities,andseveralorallofthefour
etal.(1999),forexample, suggestthatsomephysicalfeaturesof
scenarioslistedabovecouldworkintandem.
theA2597emission-linenebulaareconsistentwithwhatmightbe
AsdiscussedinSection3.4,wecannotruleoutthepossibilitythat
expectedfromagas-richminormerger.TheBCGstellarisophotes
theAGNdutycycleinA2597iscloseto100percent.Evenifthisis
do not show any obvious signs of disturbance, so a recent major
notthecase,andtheAGNisepisodicover107yrperiods,acavity’s
mergerislikelyruledout,atleastwithinthepastseveraldynamical
enthalpyreservoirshouldbedissipatedasheatintheISM/ICMona
times.
time-scaleoftheorderofthecavitylifetime(Churazovetal.2002; InFig.2weplotthe[OI]λ63µmlineprofilefromtheHerschel
Reynolds et al. 2002; Bˆırzan et al. 2004; Dunn & Fabian 2006). PACSspectroscopy(Edgeetal.2010b)inblack,overtheCO(2−1)
TheneteffectofthistimebuffercouldbethatISM/ICMheating
rotationallineprofile(inblue)fromtheIRAM30-mobservations
ratesareroughlyconstantintimeforcavityheatingmodels,even
ofA.Edge&P.Salome´ (privatecommunication,datapreviously
iftheAGNitselfisepisodicoverthesetime-scales.Ifweassume unpublished). [OI] λ63µm is one of the primary atomic coolant
thatthisiscorrect,andfurtherassumethatmostcoldbaryonsinthe linesforT(cid:2)40Kgas(Kaufmanetal.1999),andCO(2−1)canbe D
nucleuscooledfromthehotatmosphere,thenwemightconclude consideredatracerofthemolecularhydrogenreservoir.Following ow
thatlowlevelsofresidualcoolingmustpersistataroughlyconstant n
Solomonetal.(1997)andadoptingastandardMilkyWay(MW) lo
rcgaaatssee.t,oTahthinseewaBroH-ucoladncsbcteraenctitooncnsoiroseltsienengrtvworaiirtt,ehfswuceoelunlilandrgiofau(nlio)nnoeglr-(aliiiv)setaedbaordavyteh.fleIornwththaoinsf Httho2eamCCaOOss-l-iitnnoef-eClrurOemdliunmmoosiilnteyocsuoiltfayrLrh(cid:8)CayOtido=roogf3eα.n9=m×a41s.0s68oMKf(cid:3)Mkm(Ks−=k1mp1cs.82−1c±opnc0v2.3)e−r×t1s, aded from
etihnpehisoAomdGoiNcgeAinnGeAoNu2.s5T9hh7eiaisstiwnapgopuarlnoddxbicmeoacotoleinlnysgiss(tteee.angdt.ywscsitetahntaeor.uiWoreisiu,wgioigiuealsdntidroe/noqruthiivrae)t u1n09[rOeMsoI(cid:3)]lvw.edas(tdheeteHcteerdscahtelabseiagmnala-ttoth-nisoiwseavrealteiong(tHSh2/Nis)∼o9fa(cid:3)rc3s0ecb≈ut http://mn
toallowcoolingtore-triggertheradiosource. ra
strTuchteurneodtimonanthnaetrc(osocleinnagricoouiil)dipsroncoetecdoinntraovseprastiiaall,lyanddiscwreatseparned- a51n53d.5khmkapscsa)−n.1Tinwhteriitnh[OsiacI]fpuloilnslsewibiisdletcheaanstytrhmeadmlfa-emttrtaihcxeirmseydusmtvee(mFloiWcciHtByCMeG)xcorefesd4ss0h5oiff±ft-, s.oxford
dictedevenbytheearliestcoolingflowmodels(seee.g.thereview setfromthesystemicvelocityby∼+250kms−1.TheCO(2−1) jou
bhyeaFtatbhieanou1t9e9rm4)o.sWt rheigleiolonnsgo-flivceodolsocuonredswinavaesmcoorueldhothmeoogreetniceaolulys FmWayHaMlsoisesxlhigibhittlyansacrarloewdedro(w30n0s±ign5a0tukrme osf−1t)hethsoaumghetrheedparsoyfimle- rnals.o
manner,heatingbyshort-livedX-raycavityenthalpydissipationis metry (Edge et al. 2010b). The IRAM 30-m CO(2−1) beam is arg/
expected to be spatially confined to the scale and location of the 13arcsec≈20kpc,largerthantheHerschel63-µmbeam,soared t D
cavity,regardlessoftheReynoldsnumberoftheplasma(seee.g. u
wingarisingfromgasnearthecentrewouldbemoredilutedinthe rh
thereviewbyMcNamara&Nulsen2007).Inthiscase,onewould CO(2−1)profile.Averymarginal(2.6σ)CO(1−0)detectionwas am
expectcoolingtoproceedintheregionsunaffectedbylocalheat- U
alsoobtainedbyA.Edge&P.Salome´ atthesamevelocityasthe n
ing. Recently, deep X-ray observations of Perseus and A2146 by iv
e
(respectively)Fabianetal.(2011)andRusselletal.(2012)revealed rs
ity
brightX-rayfilamentswhichalonecouldbeassociatedwithasig- L
nificantfraction((cid:2)80percent)ofthetotalinferredcoolingrate.In ib
ra
Section5ofthispaper,wewillshowasimilarresultforA2597. ry
o
Ontheotherhand,O’Deaetal.(2010)studiedasampleofseven n
N
CC BCGs selected on the basis of an IR excess associated with o
v
elevatedstarformationrates,andfoundthateachtendedtopossess em
b
aweak,compactradiosource.ThecombinationofhigherSFRand e
lowerradiopowermaybeconsistentwithascenariowhereinalow r 26
stateofAGNfeedbackallowsforincreasedresidualcondensation , 20
1
from the ambient X-ray atmosphere, accounting for the elevated 3
star formation rates. This would be consistent with scenario (iii),
thoughA2597doesnotappeartobeastrongcandidate.Westress
thatscenarios(i)–(iii)arenotcontradictoryorcompetitivewithone
another,andeachcouldplayasimultaneouslyimportantrole.The
sameistrueforpossibility(iv),whichweinvestigateinmoredetail
below.
4.2 Newresultsoncoldgaskinematics–discriminating Figure2. AcomparisonoftheHerschel[OI]λ63µmlineprofile,inblack,
betweenhotandcoldaccretionscenarios with the IRAM 30-m CO(2−1) rotational line profile in blue. The [OI]
lineiscentredatthesystemicBCGredshift,andhasanintrinsicFWHMof
ThenewChandraandHerscheldatacanbeusedtobetterunder- 405±55kms−1withapossibleasymmetricredvelocityexcessoffsetfrom
standtheoriginofthe1.8±0.3×109M(cid:3)coldreservoirinA2597. thesystemicvelocityby∼+250kms−1.TheCO(2−1)FWHMisslightly
RelativetoBCGsinnon-CCclusters,CCBCGsarefarmorelikely narrower(300±50kms−1),andmayalsoexhibitaslightredasymmetry.
toharbourcentralemission-linenebulae,coldgascomponentsand ThespectralresolutionoftheCOdatais45kms−1.Bothspectrahavebeen
radiosources(e.g.Mittaletal.2009;Hudsonetal.2010,andrefer- normalized to their maximum to enable comparison of the line profiles.
encestherein).Thisstrongcircumstantialevidencesuggestsacausal Intensitiesarethereforearbitrary.
(cid:4)C 2012TheAuthors,MNRAS424,1042–1060
MonthlyNoticesoftheRoyalAstronomicalSociety(cid:4)C 2012RAS