alma mater studiorum universit`a di bologna solving the cooling flow problem through mechanical

214 Pages·2012·30.59 MB·English

ALMA MATER STUDIORUM
`
UNIVERSITA DI BOLOGNA
Facolta` di Scienze Matematiche Fisiche e Naturali
Dipartimento di Astronomia
DOTTORATO DI RICERCA IN ASTRONOMIA
CICLO XXIV (2009-2011)
SOLVING THE COOLING FLOW PROBLEM
THROUGH
MECHANICAL AGN FEEDBACK
TesidiDottorato
di
MASSIMO GASPARI
COORDINATORE: RELATORE:
Chiar.moProf. Chiar.moProf.
Lauro MOSCARDINI Fabrizio BRIGHENTI
EsameFinaleAnno2012
SCUOLADIDOTTORATOINSCIENZEMATEMATICHE,FISICHEEASTRONOMICHE
SettoreConcorsuale: 02/C1–Astronomia,Astrofisica,FisicadellaTerraedeiPianeti
SettoreScientifico-Disciplinare: FIS/05–AstronomiaeAstrofisica

To the people who believed in me
Alle persone che hanno creduto in me

Contents
Introduction 3
1 TheCoolingFlowProblem 5
1.1 HotGas . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
1.2 CoolingTime . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8
1.3 PureCoolingFlows . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8
1.4 QuenchedCoolingFlows . . . . . . . . . . . . . . . . . . . . . . . . . . 10
1.4.1 X-raySurfaceBrightness . . . . . . . . . . . . . . . . . . . . . . 11
1.4.2 TemperatureProfiles . . . . . . . . . . . . . . . . . . . . . . . . 11
1.4.3 CoolingRates . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12
1.4.4 ColdGas . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12
1.4.5 StarFormation . . . . . . . . . . . . . . . . . . . . . . . . . . . 14
2 HeatingMechanisms 17
2.1 AGNBubbles . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18
2.2 AGNShocks . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21
2.3 AGNJetsandOutflows . . . . . . . . . . . . . . . . . . . . . . . . . . . 24
2.4 Self-regulationandThermalBalance . . . . . . . . . . . . . . . . . . . . 26
2.5 Transport: ConductionandTurbulence . . . . . . . . . . . . . . . . . . . 28
3 NumericalMethods 31
3.1 FLASHcode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31
3.2 Hydrodynamics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32
3.3 TheEulerianAMRgrid . . . . . . . . . . . . . . . . . . . . . . . . . . . 34
3.4 NumericalSolver: PPM . . . . . . . . . . . . . . . . . . . . . . . . . . . 37
I
II CONTENTS
3.5 RadiativeCooling . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 41
3.5.1 ColdGasDropout . . . . . . . . . . . . . . . . . . . . . . . . . 43
3.6 AGNOutflows . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 44
3.7 AccretionandSelf-regulation . . . . . . . . . . . . . . . . . . . . . . . . 46
3.8 StellarWindsandSupernovae . . . . . . . . . . . . . . . . . . . . . . . 48
3.9 InitialConditionsandGravity . . . . . . . . . . . . . . . . . . . . . . . 50
3.9.1 GaussianPerturbations . . . . . . . . . . . . . . . . . . . . . . . 51
4 AGNFeedbackinGalaxyClusters 53
4.1 GalaxyClustersOverview . . . . . . . . . . . . . . . . . . . . . . . . . 53
4.2 SimulationSetup . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 58
4.2.1 Template: Abell1795 . . . . . . . . . . . . . . . . . . . . . . . 59
4.3 Results . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 61
4.3.1 PureCoolingFlow [cl-CF] . . . . . . . . . . . . . . . . . . . . . 61
4.3.2 ColdFeedback: (cid:15) = 5 10−4 [cl-C5m4] . . . . . . . . . . . . . . 61
×
4.3.3 ColdFeedback: (cid:15) = 10−3 [cl-C1m3] . . . . . . . . . . . . . . . . 64
4.3.4 ColdFeedback: (cid:15) = 5 10−3 [cl-C5m3] . . . . . . . . . . . . . . 64
×
4.3.5 ColdFeedback: (cid:15) = 10−2 [cl-C1m2] . . . . . . . . . . . . . . . . 66
4.3.6 ColdFeedback: (cid:15) = 5 10−2 [cl-C5m2] . . . . . . . . . . . . . . 67
×
4.3.7 ColdFeedback: (cid:15) = 10−1 [cl-C1m1] . . . . . . . . . . . . . . . . 67
4.3.8 SummaryofColdFeedback . . . . . . . . . . . . . . . . . . . . 68
4.3.9 IntermittentorContinuousFeedback . . . . . . . . . . . . . . . . 68
4.3.10 RoleoftheJetSize . . . . . . . . . . . . . . . . . . . . . . . . . 70
4.3.11 BondiFeedback: (cid:15) = 10−1 [cl-B1m1S] . . . . . . . . . . . . . . . 71
4.4 DynamicsofBestModel [cl-C5m3] . . . . . . . . . . . . . . . . . . . . . 73
4.5 X-rayObservables . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 78
4.5.1 CavitiesandShocks . . . . . . . . . . . . . . . . . . . . . . . . 79
4.5.2 IronEnrichmentandMixing . . . . . . . . . . . . . . . . . . . . 80
4.5.3 HydrostaticEquilibrium . . . . . . . . . . . . . . . . . . . . . . 81
4.6 Discussion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 83
4.6.1 ComparisonwithotherFeedbackModels . . . . . . . . . . . . . 83
4.6.2 ColdFeedback . . . . . . . . . . . . . . . . . . . . . . . . . . . 85
4.6.3 HotBondi-likeFeedback . . . . . . . . . . . . . . . . . . . . . . 87
4.6.4 BestModelsComparison . . . . . . . . . . . . . . . . . . . . . . 88
M.Gaspari PhDThesis
CONTENTS III
5 AGNFeedbackinGalaxyGroups 89
5.1 GalaxyGroupsOverview . . . . . . . . . . . . . . . . . . . . . . . . . . 89
5.2 SimulationSetup . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 94
5.2.1 Template: NGC5044 . . . . . . . . . . . . . . . . . . . . . . . . 94
5.3 Results . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 95
5.3.1 PureCoolingFlow [gr-CF] . . . . . . . . . . . . . . . . . . . . . 95
5.3.2 BondiFeedback: (cid:15) = 5 10−2 [gr-Bc5m2] . . . . . . . . . . . . . 97
×
5.3.3 HybridFeedback: (cid:15) = 5 10−2 [gr-Bi5m2] . . . . . . . . . . . . . 99
×
5.3.4 BondiFeedback: (cid:15) = 10−1 [gr-Bc1m1] . . . . . . . . . . . . . . . 101
5.3.5 HybridFeedback: (cid:15) = 10−1 [gr-Bi1m1] . . . . . . . . . . . . . . . 102
5.3.6 BondiandHybridFeedback: (cid:15) = 10−2 [gr-Bc1m2;gr-Bi1m2] . . . . 102
5.3.7 BondiandHybridFeedback: (cid:15) = 10−3 [gr-Bc1m3;gr-Bi1m3] . . . . 103
5.3.8 ColdFeedback: (cid:15) = 5 10−5 [gr-C5m5] . . . . . . . . . . . . . . 103
×
5.3.9 ColdFeedback: (cid:15) = 10−4 [gr-C1m4] . . . . . . . . . . . . . . . . 103
5.3.10 ColdFeedback: (cid:15) = 5 10−4 [gr-C5m4] . . . . . . . . . . . . . . 104
×
5.3.11 ColdFeedback: (cid:15) = 10−3 [gr-C1m3] . . . . . . . . . . . . . . . . 106
5.3.12 IntermittentFeedback . . . . . . . . . . . . . . . . . . . . . . . 107
5.3.13 ThermalFeedback . . . . . . . . . . . . . . . . . . . . . . . . . 109
5.3.14 Inflow-OutflowFeedback . . . . . . . . . . . . . . . . . . . . . 110
5.4 DynamicsandObservablesofBestModels . . . . . . . . . . . . . . . . 111
5.5 Discussion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 117
5.5.1 HotBondi-likeFeedback . . . . . . . . . . . . . . . . . . . . . . 117
5.5.2 ColdFeedback . . . . . . . . . . . . . . . . . . . . . . . . . . . 118
5.5.3 Hybridfeedback . . . . . . . . . . . . . . . . . . . . . . . . . . 119
5.5.4 RejectedModels . . . . . . . . . . . . . . . . . . . . . . . . . . 120
5.5.5 ComparisonwithotherWorks . . . . . . . . . . . . . . . . . . . 120
5.5.6 ComparisonwithGalaxyClusters . . . . . . . . . . . . . . . . . 121
6 AGNFeedbackinEllipticalGalaxies 123
6.1 EllipticalGalaxiesOverview . . . . . . . . . . . . . . . . . . . . . . . . 123
6.2 SimulationSetup . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 129
6.2.1 IsolatedElliptical . . . . . . . . . . . . . . . . . . . . . . . . . . 129
6.2.2 EllipticalwithCircumgalacticGas . . . . . . . . . . . . . . . . . 130
6.3 Results: IsolatedElliptical . . . . . . . . . . . . . . . . . . . . . . . . . 130
6.3.1 PureCoolingFlow . . . . . . . . . . . . . . . . . . . . . . . . . 131
M.Gaspari PhDThesis
IV CONTENTS
6.3.2 ColdFeedback: (cid:15) = 10−4 [iso-C1m4] . . . . . . . . . . . . . . . . 133
6.3.3 ColdFeedback: (cid:15) = 10−3 [iso-C1m3] . . . . . . . . . . . . . . . . 135
6.3.4 ColdFeedback: (cid:15) = 3.3 10−4 [iso-C3m4] . . . . . . . . . . . . . 136
×
6.3.5 X-rayObservables . . . . . . . . . . . . . . . . . . . . . . . . . 136
6.4 Results: EllipticalwithCircumgalacticGas . . . . . . . . . . . . . . . . 141
6.4.1 ColdFeedback: (cid:15) = 8 10−4 [cgg-C8m4] . . . . . . . . . . . . . . 141
×
6.4.2 X-rayObservables . . . . . . . . . . . . . . . . . . . . . . . . . 143
6.5 Discussion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 150
6.5.1 ComparisonwithotherFeedbackModels . . . . . . . . . . . . . 150
6.5.2 AGNTurbulence . . . . . . . . . . . . . . . . . . . . . . . . . . 151
6.5.3 ConcludingRemarks . . . . . . . . . . . . . . . . . . . . . . . . 152
7 MultiphaseGas 155
7.1 ColdGasOverview . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 155
7.2 SimulationSetup . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 159
7.2.1 InitialConditions . . . . . . . . . . . . . . . . . . . . . . . . . . 161
7.3 Results . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 161
7.3.1 PureCoolingFlow [r7-CF] . . . . . . . . . . . . . . . . . . . . . 162
7.3.2 AGNFeedback: tcool/tff = 7and(cid:15) = 6 10−3 [r7-i6m3] . . . . . . 164
×
7.3.3 AGNFeedback: tcool/tff = 7and(cid:15) = 10−2 [r7-i1m2] . . . . . . . . 168
7.3.4 AGNFeedback: WobblingOutflows [r7-i6m3w] . . . . . . . . . . 170
7.3.5 AGNFeedback: tcool/tff = 21and(cid:15) = 6 10−3 [r21-i6m3] . . . . . 171
×
7.3.6 AGNFeedback: tcool/tff = 21and(cid:15) = 10−2 [r21-i1m2] . . . . . . . 171
7.4 Discussion: theDetailedThermalState . . . . . . . . . . . . . . . . . . 173
8 Conclusions 181
8.1 ConsistencywithObservations . . . . . . . . . . . . . . . . . . . . . . . 182
8.2 SuccessfulFeedbackCharacteristics . . . . . . . . . . . . . . . . . . . . 184
8.3 LimitationsandFutureDevelopments . . . . . . . . . . . . . . . . . . . 187
8.4 Finale . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 190
Bibliography 191
PhDProduction 204
Acknowledgments 206
M.Gaspari PhDThesis
Introduction
O
NE of the most crucial problems of present-day astrophysics concerns the
thermodynamical evolution of the baryonic, ordinary matter. Heating processes
play a fundamental role in galaxies, groups and clusters, struggling in an intricate
but fascinating dance with its antagonist, cooling. The majority of baryons in the
universe appears to reside in the form of an almost fully ionised gas, a plasma with
temperaturesovertenmilliondegreesanddensitiesbelowoneparticlepercm3. Quantum
mechanics tells us that such plasma looses thermal energy, emitting photons, mainly due
tobremsstrahlung,recombinationandlineexcitation. Unopposedradiativecoolingwould
leadtothecoolingcatastrophe;thedenser,centralregionsofvirialisedsystemscoolfaster,
loosingpartialpressuresupportandinducingasubsonicinflowofgasfromtheperipheral
zones toward the nucleus. The increment of gas density causes a further increase of
radiative cooling. This vicious circle leads to unobserved cooling rates up to hundreds
solar masses per year, in the most massive systems. At the centre of galaxies, groups
andclusters,thehugeaccumulationofmonolithicallycondensedcoldgaswouldproduce
unrealistic surface brightness peaks and star formation rates. This is the cooling flow
problem. Since every important baryonic structure, like molecular clouds, stars, dust and
planets,willlaterrisefromthehotplasmacrucible,itiscrucialtofindandunderstandthe
counterbalancingprocess,i.e.heating.
The last-generation (X-ray) telescopes, Chandra and XMM-Newton, have provided a
striking hint to the solution of the cooling flow problem. We now see the spectacular
and powerful interactions of the supermassive black hole, residing at the centre of the
active galactic nucleus (AGN), with the surrounding medium, in the form of buoyant
bubbles, shock cocoons, metals dredge-up, turbulence, jets and nuclear outflows. Even if
fromanenergeticpointofviewtheAGNiscapabletobalanceradiativelosses,numerous
questionsarefartobesettled. Inprimis,whatisdominantengineofheating? Howcanthe
AGN energy couple to the interstellar/intracluster plasma? How can the galaxy, group or
clustermaintainastateofquasithermalequilibriumforseveralGyr? Whatistheoriginal
feedbackprocessthatgeneratesthewealthofobservationalfeatures? Whydoweobserve
extended(filamentary)andnuclearcoldgas,eveninthepresenceofstrongheating?
WiththepresentThesis,Iintendtodeeplyinvestigatethepreviousquestions,focusing
on the solution of the cooling flow problem, i.e. dramatically quenching the cooling
rates for several Gyr without destroying the cool-core structure. The main theoretical
1
2 Introduction
hypothesis is that the dominant feedback process should be mechanical and anisotropic,
originated from massive subrelativistic AGN outflows. The natural self-regulation may
beprovidedbylinkingthepropertyofthecoolinggastotheinjectionoffeedbackenergy.
Thiscentralideawillbeseverelytestedviathree-dimensionalhydrodynamicsimulations,
carried out via the state-of-the-art Eulerian code FLASH, substantially modified and
upgraded to study astrophysical phenomena, as outflows, shocks, cooling, turbulence,
thermalinstabilities,andmultiphasegas.
TheThesisisorganisedasfollows.
In Chapter 1, I first review the key properties of the hot plasma, residing in the
•
majority of the cosmic virialised structures, as clusters, groups and ellipticals.
I focus on the theoretical background essential to understand what is a classic
cooling flow. The second part describes insteadthe observational evidences of real,
quenchedcoolingflows.
In Chapter 2, I present an essential review on the cooling counterpart, heating.
•
The attention is mainly given to the various manifestation of AGN feedback in hot
halo systems, including buoyant bubbles, shocks, jets/outflows, but also transport
processesasconductionandturbulence.
In Chapter 3, I describe the entire numerical methods, necessary to carry out the
•
simulations via the FLASH code. After a brief introduction on hydrodynamics,
I introduce the AMR grid structure and how the Euler equations are solved (PPM
scheme). Idiscussthen,indetail,thekeyimplementationofradiativecooling,AGN
outflows,theself-regulation,stellarevolutionandtheinitialconditionsetup.
InChapter4,Ibegintopresenttheresultsofthesimulationson(mechanical)AGN
•
feedback in galaxy clusters, after a brief overview of these systems. The ultimate
aim of the investigation is to solve the cooling flow problem, at the same time
avoidingoverheatingandreproducingfundamentalfeatures,ascavities,shocksand
metal inhomogeneities. As in the next Chapters, I present an in-depth discussion
of the merits and flaws of all models, with a critical eye toward observational
concordance.
In Chapter 5, I continue to analyse the 3D simulations on massive AGN outflows,
•
self-regulated by cold and and hot accretion, this time in a typical galaxy group.
I present the best models dynamics and observables, thoroughly discussing the
propertiesofthefeedbackself-regulation.
InChapter6,Iclosetherangeoftestedhothalosystems,studyingtheself-regulated
•
AGN outflows also in (isolated and massive) elliptical galaxies. It is important to
solve the cooling flow problem on every scale. In fact, in less bound objects, the
feedback seems to have more dramatic consequences. Particular attention is given
tothegeneratedX-rayfeatures.
In Chapter 7, I test the idea that multiphase gas is the direct consequence of the
•
AGN feedback. The recurrent outflows may induce substantial turbulence, leading
to nonlinear thermal instabilities, with the condensation of the hot phase into cold
M.Gaspari PhDThesis