Residual Cooling and Persistent Star Formation Amid Active Galactic Nucleus Feedback in Abell

21 Pages·2017·12.95 MB·English

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Physics and Astronomy Faculty Publications Physics and Astronomy
8-1-2012
RReessiidduuaall CCoooolliinngg aanndd PPeerrssiisstteenntt SSttaarr FFoorrmmaattiioonn AAmmiidd 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., "Residual Cooling and
Persistent Star Formation Amid Active Galactic Nucleus Feedback in Abell 2597" (2012). Physics and
Astronomy Faculty Publications. 32.
https://uknowledge.uky.edu/physastron_facpub/32
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https://doi.org/10.1111/j.1365-2966.2012.21278.x
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Published in Monthly Notices of the Royal Astronomical Society, v. 424, issue 2, p. 1042-1060.
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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/32
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 Do
3ChesterF.CarlsonCenterforImagingScience,54LombMemorialDrive,Rochester,NY14623,USA wn
4Harvard–SmithsonianCenterforAstrophysics,60GardenStreet,Cambridge,MA02138,USA loa
5RadcliffeInstituteforAdvancedStudy,10GardenStreet,Cambridge,MA02138,USA de
d
6NavalResearchLaboratoryRemoteSensingDivision,Code72134555OverlookAvenueSW,Washington,DC20375,USA fro
7DepartmentofAstronomy,UniversityofVirginia,POBox400325,Charlottesville,VA22904-4325,USA m
8DepartmentofAstronomy,UniversityofMichigan,AnnArbor,MI48109,USA http
910OPbhsyesrivcastoainrdeAdestProanroism,LyEDReMpaAr,tmCeNnRt,SM,6ic1hAigva.ndeSlt’aOtebUsenrivvaetrosiirtey,,7E5a0s1t4LaPnasriinsg,,FMraIn4c8e824-2320,USA ://mn
11DepartmentofPhysics,DurhamUniversity,DurhamDH13LE ras
12InstituteofAstronomy,MadingleyRoad,CambridgeCB30HA .ox
13DepartmentofPhysics,UniversityofKentucky,Lexington,KY40506,USA ford
14PhysicsandAstronomyDepartment,WaterlooUniversity,200UniversityAvenueW.,Waterloo,ONN2L2G1,Canada jo
u
15ASTRON,NetherlandsInstituteforRadioAstronomy,POBox2,7990AADwingeloo,theNetherlands rn
16DepartmentofPhysicsandAstronomy,UniversityofRochester,Rochester,NY14627,USA als
.o
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Accepted2012May9.Received2012May8;inoriginalform2012March1 n
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ity
ABSTRACT of K
NewChandraX-rayandHerschelFar-Infrared(FIR)observationsenableamultiwavelength e
n
studyofactivegalacticnucleus(AGN)heatingandintraclustermedium(ICM)coolinginthe tuc
k
brightest cluster galaxy (BCG) of Abell 2597 (z = 0.0821). The new Chandra observations y L
revealthecentral(cid:2)30kpcX-raycavitynetworktobemoreextensivethanpreviouslythought, ibra
andassociatedwithenoughenthalpytotheoreticallyinhibittheinferredclassicalcoolingflow. rie
s
o
Nevertheless, we present new evidence, consistent with previous results, that a moderately n
A
strongresidualcoolingflowispersistingat4–8percentoftheclassicallypredictedratesina u
g
u
spatiallystructuredmanneramidthefeedback-drivenexcavationoftheX-raycavitynetwork. st 2
New Herschel observations are used to estimate warm and cold dust masses, a lower limit 0, 2
gas-to-dust ratio and a star formation rate consistent with previous measurements. [OI] and 014
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
o
ontime-scalesmuchshorterthanaGyrwithinaradiusof∼100kpc. 2003;Bˆırzanetal.2004;Robinsonetal.2004;Dursi&Pfrommer w
n
Simplemodelspredictthatrunawayentropylossbygaswithinthis 2008;Fabianetal.2008;Gittietal.2011).Thephenomenonislikely lo
a
d
radius accompanies subsonic, nearly isobaric compression by the episodicataratecoupledtotheAGNdutycycle,andtotalenergy e
d
ambienthotreservoir,drivingalong-livedclassicalcoolingflowon inputwhensummedovertheclusterlifetimecanrangefrom∼1055 fro
tothecentralbrightestclustergalaxy(hereafterBCG;seecooling to1061erg.Inprinciple,thisisenoughtoreplenishthetotalenergy m
h
flow reviews by Fabian 1994; Peterson & Fabian 2006). In these budget of ICM radiative losses for an average of the CC cluster ttp
‘cool core’ (CC) clusters, catastrophic condensation of the ICM population,althoughthespatialdistributionandthermalizationof ://m
shoulddriveextremestarformationrates(102–103M(cid:3)yr−1)amid this energy is one of several important problems that challenge nra
massive cold gas reservoirs (∼1012M(cid:3)) in the BCG, and high- the model(e.g. McNamara&Nulsen2007, 2012,and references s.o
x
resolution X-ray spectroscopy should detect bright coolant lines therein). The physics coupling AGN mechanical energy to ICM fo
stemmingfrom(cid:2)103M(cid:3) cascadesofmultiphasegascondensing entropy remain poorly understood, and thermal conduction, gas rdjo
from the hot atmosphere. Yet three decades of searches for these sloshing and dynamical friction likely play additional important urn
a
expectedcoolingflowmasssinksreturnedwithresultsthatwereor- roles (e.g. Sparks, Macchetto & Golombek 1989; Ruszkowski & ls
.o
dersofmagnitudebelowpredictions,consistentonlywithresidual Begelman 2002; Voigt et al. 2002; Brighenti & Mathews 2003; rg
coolingat∼1–10percentoftheexpectedrates(e.g.Allen1969, El-Zant, Kim & Kamionkowski 2004; Soker, Blanton & Sarazin a/
1995;DeYoung&Roberts1974;Baan,Haschick&Burke1978; 2004; Voigt & Fabian 2004; Sparks et al. 2009; Morsony et al. t U
n
Haynes,Brown&Roberts1978;Peterson1978;Shostaketal.1980; 2010; Parrish, Quataert & Sharma 2010; ZuHone, Markevitch & ive
O’Dea&Baum1987,1997;McNamara&O’Connell1989;O’Dea Johnson2010;Blantonetal.2011;Sparksetal.2012). rsity
et al. 1994a; O’Dea, Payne & Kocevski 1998; Peres et al. 1998; o
Mittazetal.2001;Petersonetal.2001,2003;Tamuraetal.2001; f K
1.1 ResidualcoolingandstarformationamidAGNfeedback en
Sakelliouetal.2002;Xuetal.2002;Edge&Frayer2003;Bregman tu
c
&Lloyd-Davies2006;Sandersetal.2008). Criticaldetailsoftheheatingandcoolingfeedbackloopareencoded ky
AttemptstoreconciletheseresultswiththehighX-rayluminosi- inthemass,energyandtime-scalebudgetsofthelow-temperature, Lib
tiesandlonglifetimesassociatedwiththeCCphasehaveinvoked high-densitygasphasespreferentiallyfoundinCCBCGs,suchas ra
non-gravitationalheatingmechanismstoinhibitorreplenishanav- filamentaryforbiddenandBalmeremission-linenebulaeand∼109– ries
erage∼90percentofICMradiativelossesovertheclusterlifetime 1010M(cid:3)reservoirsofbothvibrationallyexcitedandcold1molec- on
A
(e.g.reviewbyPeterson&Fabian2006).Onepromisingcandidate ular gas (e.g. Hu, Cowie & Wang 1985; Baum 1987; Heckman u
g
forquenchingcoolingflowsintheinnermostregionsofcoolcores etal.1989;Jaffe&Bremer1997;Donahueetal.2000;Edge2001; us
isafeedbackloopregulatedbythemechanicaldissipationofactive Jaffe, Bremer & van der Werf 2001; Edge et al. 2002; Wilman t 20
galacticnucleus(AGN)power(e.g.Rosner&Tucker1989;Baum et al. 2002; McNamara, Wise & Murray 2004; Jaffe, Bremer & , 2
0
1
&O’Dea1991;Churazovetal.2002;Bˆırzanetal.2004;Dunn& Baker2005;Egamietal.2006;Raffertyetal.2006;Salome´ etal. 4
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
o
Oonketal.2011). H2 component, inferred from CO observations2 (e.g. Edge 2001; wn
Estimated star formation rates range from a few to tens of so- Salome´ & Combes 2003), as well as a young stellar component loa
d
lar masses per year, and strongly correlate with upper limits on cospatialwithanHα-brightfilamentaryemission-linenebula(e.g. ed
spectroscopically derived ICM mass deposition rates, as well as Heckman et al. 1989; Voit & Donahue 1997; Koekemoer et al. fro
m
CO-inferred molecular gas masses (e.g. O’Dea et al. 2008). This 1999;O’Deaetal.2004;Oonketal.2011).Thesefeaturesreside h
suggestsadirectcausalconnectionbetweenreducedcoolingflows amid a network of prominent X-ray cavities (McNamara et al. ttp
and star formation, as BCGs with young stellar populations are 2001; Clarke et al. 2005), making A2597 an ideal subject for ://m
n
always found in CC clusters (Bildfell et al. 2008; Loubser et al. studiesofAGN/ISMinteractions(Tremblayetal.2012).Forthese ra
s
2009).Newevidencesuggeststhatstarformationoccurswhenmul- reasonsandothers,A2597enjoysalonghistoryofcross-spectrum .o
x
tiphasecloudsandfilamentsprecipitateoutoftheICMasitscentral analysis in the literature (X-ray – Crawford et al. 1989; Sarazin fo
entropydropsbelowacriticalthreshold((cid:2)20–30keVcm−2;Cav- et al. 1995; Sarazin & McNamara 1997; McNamara et al. 2001; rdjo
u
agnolo etal. 2008; Raffertyetal. 2008; Voit et al. 2008; Sharma Clarkeetal.2005;Morris&Fabian2005;UV/optical–McNamara rn
a
etal.2011;Gaspari,Ruszkowski&Sharma2012). &O’Connell1993;DeYoung1995;Voit&Donahue1997;Cardiel ls
.o
Butwhilethepathwayofentropylossfromhotambientmedium etal.1998;Koekemoeretal.1999;McNamaraetal.1999;Oegerle rg
to cold star-forming clouds may be strongly influenced by AGN etal.2001;O’Deaetal.2004;Jaffeetal.2005;Oonketal.2010, at U/
feedback,itisnotknownwhetherresidualcoolingpersistsatcon- 2011;IR–McNamara&O’Connell1993;Voit&Donahue1997; n
iv
stantlowlevelsorinelevatedepisodesanti-correlatedtotheAGN Koekemoeretal.1999;McNamaraetal.1999;O’Deaetal.2004; e
rs
duty cycle (e.g. O’Dea et al. 2010; Tremblay 2011). Moreover, Jaffeetal.2005;Donahueetal.2007,2011;sub-mm–Edge2001; ity
modelsinvokingradio-modefeedbacktoquenchcoolingflowsig- Salome´ & Combes 2003; Edge et al. 2010a,b; radio – O’Dea, of K
natures such as star formation must be reconciled with evidence Baum&Gallimore1994b;Sarazinetal.1995;Tayloretal.1999; e
n
that in several systems (e.g. Abell 1795 and Abell 2597; O’Dea Pollack,Taylor&Allen2005;Clarkeetal.2005). tu
c
et al. 2004), the propagating radio source may trigger compact, InSection2wedescribethenewandarchivalmultiwavelength ky
L
short-duration starbursts as it propagates amid a dense medium observationsusedinthispaper.InSection3weusethenewChandra ib
(Me.cgN.aEmlmareag&reeOn’C&onEnlmelelg1r9e9e3n;1O9’7D8e;aVeotiatl.12908084;;DBeatYchoeulndgor1e9t8a9l;. Xby-ruasyinogbstherevkaptico-nsscatloeacsasveimtybnleetawnorAkGaNsafeloewdbearclkimeintecraglyorbimudegteert raries
o
2007; Holt, Tadhunter & Morganti 2008; Holt et al. 2011). The to the AGN kinetic energy input. In Section 4 we present new n A
picture is further complicated by the role played by (e.g.) ther- HerschelFIRdataandusethemtoplaceconstraintsontheresidual u
g
u
malconductionandcoldaccretionscenarioslikegas-richmergers, coolingflow.Theseresultsareusedtoframeadiscussiononstar s
t 2
whoseimportancerelativetoresidualhot-modeICMcoolinghas formation,whichwepresentinSection5.Aconcludingdiscussion 0
drivenadebatethatisstillunsettledafterthreedecades(e.g.Sparks and summary are provided in Sections 6 and 7. Throughout this , 20
etal.1989,2012;Holtzmanetal.1996).Advancesinunderstanding work,weadoptH0=71h−711kms−1Mpc−1,(cid:5)M=0.27and(cid:5)(cid:6)= 14
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
D
HST ACS SBC F150LP(FUV) 8141s 11131 2008Jul21 Jaffe 2 o
w
··· STIS FUVMAMA F25SRF2(Lyα) 1000s 8107 2000Jul27 O’Dea 3 n
··· WFPC2 ··· F410M 2200s 6717 1996Jul27 O’Dea 4 loa
d
··· WFPC2 ··· F450W 2500s 6228 1995May07 Trauger 5 ed
··· WFPC2 ··· F702W(Rband) 2100s 6228 1995May07 Trauger 5 fro
··· NICMOS NIC2 F212N 12032s 7457 1997Oct19 Donahue 6 m
··· NICMOS NIC2 F160W(Hband) 384s 7457 1997Dec03 Donahue 6 http
ESOVLT SINFONI ··· Kband 600s 075.A-0074 2005Jul/Aug Jaffe 7 ://m
Mid-/far-infraredobservations nra
Spitzer IRAC Mapping 3.6,4.5,5.8,8µm 3600s(each) 3506 2005Nov24 Sparks 8 s.o
x
··· MIPS ··· 24,70,160µm 2160s(each) 3506 2005Jun18 Sparks 8 fo
Herschel PACS Photometry 70,100,160µm 722s(each) 13421871(18-20) 2009Nov20 Edge 9 rdjo
··· SPIRE Photometry 250,350,500µm 3336s 1342187329 2009Nov30 Edge 9 urn
··· PACS Spectroscopy [OI]λ63.18µm 6902s 1342187124 2009Nov20 Edge 10 als
······ ······ ······ [[ONIIIII]]λλ18281.3.96µµmm 77388940ss 11334422118888974023 22000190DJaenc0340 EEddggee 1100 a.org/
··· ··· ··· [OIB]λ145.52µm 7382s 1342188704 2009Dec30 Edge 10 t U
··· ··· ··· [CI]λ157.74µm 6227s 1342187125 2009Nov20 Edge 10 niv
··· ··· ··· [SiI]λ68.47µm 11834s 1342210651 2010Dec01 Edge New ers
Radioobservations ity
o
NRAOVLA ··· Aarray 8.44GHz 15min AR279 1992Nov30 Roettiger 11 f K
··· ··· Aarray 4.99GHz 95min BT024 1996Dec7 Taylor 12,13 en
··· ··· Aarray 1.3GHz 323min BT024 1996Dec7 Taylor 12,13 tuc
k
··· ··· Aarray 330MHz 180min AC647 2003Aug18 Clarke 13 y L
··· ··· Barray 330MHz 138min AC647 2002Jun10 Clarke 13 ib
ra
rie
s
o
(128ks flare-free) in combined effective exposure time, were re- scopicresolution,isalsousedtoplaceconstraintsonthecoldgas n
A
ducedusingthestandardCIAOv4.2threadswithv4.3.1ofthecal- kinematics. ug
ibration data base. More details can be found in Tremblay et al. us
(2012), which presents the spatial and spectral analysis of these 3 AGN FEEDBACK ENERGY BUDGET t 20
newobservations. , 2
Kiloparsec-scaleX-raycavitiescanbeusedaslowerlimitcalorime- 01
Herschel Space Observatory observations of A2597 were ob- 4
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.
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Figure1. Topleft:exposure-corrected0.5–7keVimageofthethreemergedChandraobservations(seeTable1).Thedatahavebeensmoothedwithan t 20
adaptiveGaussiankernel.Blackcontoursareoverlaidtobettershowthespatiallyanisotropicnatureoftheemission.Theinnermostcontourmarksafluxof , 2
4.6×10−7photonss−1cm−2pixel−1,andthecontoursmoveoutwardswithafluxdecrementof2.0×10−8photonss−1cm−2pixel−1.Topright:thesame 014
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 D
adoptedfromChurazovetal.(2001)bye.g.Bˆırzanetal.(2004). o
strongradio/X-rayspatialcorrelationsthatareevidentinthisfig- Finally,cavityagescanbeconstrainedbyestimatingthetimere- wn
ure.Wenotethattheseunsharpmaskedgeenhancementmethods quiredtorefillthevolumedisplacedbyabubbleofradiusr asit load
(particularlymethod1)areinherentlynoisy,andintroduceartefacts risesaheightequaltoitsdiameter, ed
thatcomplicateaquantitativemorphologicalanalysis.Thesignif- (cid:4) (cid:4) fro
m
itchaenucne-porfotcheessoebdsedravtead.Wfeeatsuhreoswmthuesstethmeroesftolyreabsevieeswtiminagteadidfsrofomr trefill(cid:9)2R GM(r<R) =2 gr, (3) http
the X-ray cavities discussed in this section. We do note that the ://m
processedimagesshownheredonotsignificantlydifferinapparent whereM(<R)isthemassenclosedwithinasphereofradiusR. nra
morphologyfromtheun-processedrawChandradatathatcanbe Bˆırzanetal.(2004)madeallthreeestimatesfortheNEandW s.o
x
seeninfig.2ofTremblayetal.(2012). ghost cavities in A2597 (features 1 and 3 in Fig. 1, bottom right fo
InthebottomrightpanelofFig.1welabelthesixfeaturesthatare panel), using the early short (40 ks) Chandra observation. So as rdjo
associatedwith(cid:3)10σdeficitsorexcessesrelativetothelocalmean. to provide an independent check of their results using the deeper urn
Thesignificanceofthesefeatureswasestimatedbycomparingun- X-ray data, we follow their procedure almost exactly, and repeat als
smoothed counts in like-sized regions at the same cluster-centric their calculations for the M01 ghost cavities, the western large .org
rmadoinulsa.bTehlraonudgnhaomutet.hTishpeasepearrew:e(1r)eftehret‘oMth0e1sewfeesateturnregshwoistthcaavciotmy’-, caanvdit(y6)(f(eaastularebsel1leadnidn2F)i,ga.s1w).eLllikasetBhˆıerznaenwelytadle.t(e2c0te0d4)c,awvietieasdo(4p)t at Un/
(2) the ‘C05 X-ray tunnel’, (3) the ‘M01 northern ghost cavity’, theA2597BCGstellarvelocitydispersionofσ ≈224±19kms−1 ive
(4) the ‘eastern ghost cavity’, (5) the ‘cold filament’ and (6) the fromSmith,Heckman&Illingworth(1990)inourcalculationof rsity
‘C05filamentbasecavity’.Forclarity,thesenamesandlabelswill thelocalgravitationalaccelerationg: of K
be used consistently throughout this paper. Feature (2), the ‘cold 2σ2 en
filament’,isdiscussedinsection5ofTremblayetal.(2012)inthe g(cid:9) , (4) tu
contextofAGN/ISMinteractionsandmultiphasegasdredge-upby R cky
L
theradiosource. assumingthatthegalaxyisanisothermalsphere.InTremblayetal. ib
While(for‘historical’reasons)welabelfeatures(1)and(2)in- (2012) we calculate a local value for g by estimating the total ra
dependently,ourdeeperdatamakeitclearthatwesternghostcavity enclosedgravitatingmassfromaβ-modelfittedtotheX-raysur- ries
o
describedbyM01andC05ispartofalarger‘teardrop’shapedcav- face profile. For this discussion however, it is sufficient to adopt n A
ity ∼25kpc in projected length (C05 originally suggested this in the Bˆırzan et al. (2004) method for estimating g (the two meth- u
g
u
theirdiscussionofan‘X-raytunnel’).Thischangestheinterpreta- ods turn out to be roughly consistent at the radius of the X-ray s
tionoftheAGNoutbursthistory(relativetotheconclusionsdrawn cavitynetworkanyway).UnlikeBˆırzanetal.(2004),weusekTin- t 20
inM01),whichwewilldiscussbelow.Soastoenablecomparison ferredfromthecavitypositionsontheX-raytemperaturemappre- , 20
1
withpastpapers(e.g.M01;Bˆırzanetal.2004;Raffertyetal.2006) sentedinTremblayetal.(2012)tocalculatethesoundspeedinthe 4
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
o
energydensities(equipartition),asteepspectralindexof−2.7be- w
3.3 Cavityheatingenergyreservoir tween 1.3 GHz and 330 MHz, and that the source is a uniform nloa
d
Incolumn9ofTable2wecalculatethemeaninstantaneouspower prolate cylinder with a filling factor of unity. This model yields ed
ofeach4cpavVityPcav, tahemrminaimlpurmesseunreergoyf5m×ag1n0e−t1ic1dfiyenldcmst−re2n.gWthenoofte29thµaGteqaunidpaartintoionn- h from
Pcav= (cid:10)t(cid:11) , (5) m20a0y2)b.eFaulrethsse-rtmhaonr-ei,ddeaelepaessrummuplttiiobnanindtrhaidsiocaosebs(eer.gva.tFioanbsianareetrael-. ttp://m
where(cid:10)t(cid:11)istheaverageofthecavityageslistedincolumns6–8.We quired to better assess the spectral index of the source across the nra
haveassumedthecavitiesarefilledwitharelativisticplasma,such westernlargecavity. s.o
x
thattheirenthalpycanbeapproximatedas4pV(e.g.McNamara& The lower end of the 330-MHz lifetime range quoted above fo
Nulsen2007). (t330MHz (cid:3) 8 × 106yr) is significantly shorter than the estimated rdjo
u
The total sum of all cavity thermal energies (pV)listedin col- buoyant rise time of the western large cavity it fills (see Table 2, rn
umn5is4.4×1058erg.Thisservesasarough,lowerlimitestimate column7).Ifweassumethatthisistheactualageofthesource,and als
.o
onthekineticenergyinjectedbytheAGNintotheambientX-ray furtherassumethattheestimatedageofthewesternlargecavityis rg
gpaasstdtwuroinogrmthoere(ae)pcisuordreenstoAfaGcNtiveitpyi.sTohdiesiosrcploesrehatopsth(ebi)ndfeurrriendgmthee- rtrooungshilnytchoercreacvti,tythoern(bw)earneeqwuierepi(sao)dienosfitauctriev-iatycctoelfeereadtiothneopflaeslemca- at Un/
chanicalenergyofthecentral8.4-GHzradiosource,whichSarazin intoanalreadypre-establishedcavity(which,ifempty,shouldcol- ive
etal.(1995)estimatedtobe9×1057erg.Inprinciple,theroughly lapseonasound-crossingtime(cid:2)107yr).Aswewillelaborateupon rsity
estimatedmechanicalinputfromtheradiosourcecouldbecapable below,thereislittlesupportingevidencefavouringeitherofthese o
ofaccountingfortheenergybudgetinferredfromtheX-raycavi- scenarios. f Ke
n
ties,ignoringtime-scalearguments.Whetherornotthesecavities A‘radiosourceyoungerthanthecavity’scenariocouldalsobe tu
c
havebeenproducedbyoneormoreAGNepisodesisthesubjectof possibleifadiabaticand/orinverseComptonlossesdominateover ky
thefollowingsection. thesynchrotronprocesses,whichwouldresultintheradiosource Lib
fading on a time-scale shorter than the synchrotron lifetime. The ra
importanceoftheseprocessesrelativetosynchrotronlossesdepends ries
3.4 TheAGNdutycycleandheatingtime-scalebudget o
ontheBfieldstrengthandunknowndetailsofhowtheradiosource n
A
Anetworkofmultiplecavitiesfoundatvaryingcluster-centricradii fillsthebubble.InverseComptonlossesbecomemoreefficientthan u
g
(aswefindinA2597)maybeproducedwithanepisodicallyvarying synchrotronlosseswhentheBfieldisextremelyweak(B <1µG; us
AGN,transitioningbetweeneither‘on’and‘off’orhighandlow e.g.Fabianetal.2002),andadiabaticlossesarenotlikelyalimiting t 20
modes.Cyclingtimesbetweenthetriggeringofradioactivity,the factorbecausethewesternlargecavityislikelyrisingatlessthan , 20
1
onsetofquiescenceandthesubsequentre-ignitionofactivityare thesoundspeed(notetheabsenceofanydetectedfastshocksinthe 4
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
o
thatthebendisduetotheinteractionoftheradiosourcewiththe tantconsiderationssuchashowthisenthalpymightbedissipated w
n
ambientdensegaseousmedium,eitherbydeflectionorback-flow anddistributedintheambientgas.OurfindingthattheX-raycavities loa
d
alongpre-establishedpressuregradients(e.g.Sarazinetal.1995; areassociatedwithenoughenergytoinhibitthepredictedclassical ed
Koekemoeretal.1999;O’Deaetal.2004;Clarkeetal.2005;Oonk coolingflowluminosityisconsistentwithpreviousresults(Bˆırzan fro
m
etal.2010). etal.2004;Dunn&Fabian2006). h
ttp
://m
3.5 Blackholeaccretionrate n
ra
4 NEW EVIDENCE SUPPORTING A RESIDUAL s
If the AGN is indeed nearly steady state, the central black hole .o
(BH) requires a stable supply of gas from the ambient accretion COOLING FLOW MODEL FOR A2597 xfo
reservoir.Assumingamass-to-energyconversionefficiencyof(cid:9)= Intheprevioussection,weestimatedthattheX-raycavitynetwork rdjo
u
0.1(Wiseetal.2007),andassumingthattheenergyassociatedwith is associated with enough enthalpy to (in principle) replenish a rn
a
theX-raycavitiesisprovidedbytheAGN,thesumofmeaninstan- significantfractionoftheradiativelossesassociatedwithaclassical ls.o
rtaanteeooufscavitypowers(Pcav)re(cid:5)quire(cid:6)satime-averagedBHaccretion cBoCoGlinsgtrfloonwgl.yHsouwgegveesrt,tthhaetwsoarmmeacnodolcionlgdfgraosmphthaeseasminbtihenetAX2-5r9ay7 at Urg/
M˙acc∼ P(cid:9)cca2v ∼0.003−0.03 0(cid:9).1 −1 M(cid:3)yr−1, (6) adtimscousspshtehriesphoasssmibailnitayghedereto. persist,evenamidAGNheating.We nivers
wherecisthespeedoflight.UsingtheMBH−σ relation(Magor- ity o
rian et al. 1998; Ferrarese & Merritt 2000; Gebhardt et al. 2000) f K
e
with the K-band host luminosity and stellar velocity dispersion 4.1 HowmightcoolingpersistamidAGNfeedback? ntu
yieldsaroughBHmassestimateof∼3×108M(cid:3),forwhichthe ck
corresponding Eddington accretion rate would be ∼10M(cid:3)yr−1 AsmentionedinSection1,resultsfromXMM–NewtonandFUSE y L
areconsistentwithamoderatelystrongresidual(sometimescalled ib
(isRsatfrfoenrtgylyetsualb.-2E0d0d6i)n.gTtohnis,scuogngsiessttesntthwatitthhepaacstcrreetsiuolntsreavtee,niffostrevaedryy, ‘reduced’) cooling flow with a mass deposition rate of ∼30 ± rarie
powerful AGN (e.g. Hydra A; Wise et al. 2007). If the AGN is 15M(cid:3)yr−1at∼30kpcto90±15M(cid:3)yr−1at∼100kpc(Oegerle s on
insteadstronglyvariableorepisodic,thengastransporttotheBH et al. 2001; Morris & Fabian 2005). The cooling luminosity as- A
couldbenon-steadyandtheactualaccretionratecouldvary. sociated with this residual cooling flow is LCool,Resid ≈ (0.3–1) × ugu
1044 ergs−1.Aswith15–30percentofCCBCGs(dependingon st 2
3.6 Thereisenoughenergytoquenchaclassicalcoolingflow tshuebsstaamntpialel;1.e8.g±.S0a.3lo×me´10e9tMal(cid:3).2r0e0s6e)r,vothireoAf2c5o9ld7HBC(Ginfhearrrebdoufrrosma 0, 20
2 1
4
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