the evolution of agn and their host galaxies

215 Pages·2016·8.3 MB·English

T AGN
HE EVOLUTION OF AND
THEIR HOST GALAXIES
By
ELENI KALFOUNTZOU
Athesissubmittedto theUniversityofHertfordshire
inpartialfulfilmentoftherequirementsofthedegreeof
DoctorofPhilosophy
July2015
ii
c EleniKalfountzou,2016.
(cid:13)
Typesetin LATEX2ε.
Abstract
Active galaxies have been in the forefront of astronomic research since their first discov-
ery, at least 50 years ago (e.g. Schmidt, 1963; Matthews&Sandage, 1963). The putative
supermassiveblack hole (SMBH) at their center characterizes their properties and regulates
the evolution of these objects. In this thesis, I study the ‘demographics’ and ‘ecology’ of
active galactic nuclei (AGN) in the context of their evolution and the interaction with their
environments(mainlytheirhostgalaxy).
ThenumberdensityofAGNhasbeenfoundtopeakat1 < z < 3(e.g.Uedaet al.,2003;
Hasingeret al., 2005; Richards et al., 2005; Aird etal., 2010), similar to the star formation
history (e.g. Silvermanet al., 2008a; Aird etal., 2010). However, when taking into account
obscuration, faint AGN are found to peak at lower redshift (z 2) than that of bright AGN
≤
(z 2 3; e.g. Hasingeret al., 2005; Hopkinset al., 2007; Xueetal., 2011). This qualita-
≈ −
tive behaviour is also broadly seen in star-forming galaxies (e.g. Cowieet al., 1996) and is
often referred to as ‘cosmic downsizing’, although this term has developed a number of us-
ageswithrespecttogalaxies(e.g.Bundy et al.,2006;Cimattietal.,2006;Faber etal.,2007;
Fontanotet al., 2009). Though this behaviour is well established up to z 3, the nature of
≈
howand whentheinitialseed oftheseAGNswere formedremains an openquestion.
Forthisstudy,IuseChandrasurveystostudysomeofthemostdistantAGNintheUni-
verse(z > 3). Thecombinationoftwo different sizeand depth Chandrasurveys(Chandra-
COSMOSandChaMP)providesmewiththelargestto-datez > 3AGNsample,overawide
rangeofrest-frame2-10keVluminosities[log(L /erg s−1) = 43.3 46.0]andobscuration
X
−
(N = 1020 1023 cm−2). I find strong evidence about a strong decline in number density
H
−
of X-ray AGN above z 3, and also the association of this decline with a luminosity-
≈
dependentdensityevolution(LDDE;e.g. Gilliet al., 2007). Especiallyat highredshifts,the
different evolution models predict quite different numbers of AGNs. The large size and the
wide X-ray luminosity range of this sample reduces the uncertainties of previous studies at
similarredshifts making it possibleto distinguishbetween the different models and suggest
thatobservationsappear tofavourtheLDDEmodel.
TheobservedAGNdownsizingbehaviourseenviathemeasuredX-ray luminosityfunc-
tion(XLF)couldariseduetochangesinthemassofthetypicalactiveSMBHand/orchanges
inthetypicalaccretionrate. ButhowdoesthegrowthofSMBHsovercosmictimeinfluence
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its environment? A powerful way to address this question is to compare the host galaxy
propertiesoverawiderangeofAGN andaccretion rate types.
Radio-jets are one of the most prominent constituents of AGN as they can interact di-
rectly with the host galaxy. Although AGN with radio jets are rare (they make up to 10 per
cent of the total AGN population) radio galaxies make up over 30 per cent of the massive
galaxy population and it is likely that all massive galaxies go through a radio-loud phase,
as the activity is expected to be cyclical (e.g Best et al., 2005). It is therefore, important to
investigatetheimpactofradiojetsonthehostgalaxyandparticularlythestarformation. The
method I follow focuses on the comparison of the host galaxy properties between optically
selected quasar samples, with and without strong radio emission associated with powerful
radio-jets, matched in AGN luminosity. Herschel far-infrared observations are used to trace
the star formation in the host galaxy, providing minimal AGN contamination. In my first
approach, I have constructed a sample of radio-loud and radio-quiet quasars from the Faint
ImagesRadioSkyatTwenty-onecentimetres(FIRST)andtheSloanDigitalSkySurveyData
Release 7 (SDSS DR7), overtheH-ATLAS Phase 1 Area (9h, 12h and 14.5h). The main re-
sult of this work is that RLQs at lower AGN luminosities tend to have on average higher
FIRand250-µmluminositywithrespecttoRQQsmatchedinAGNluminosityandredshift.
However, evolution effects could be strong as the quasars in this samplecover a wide range
of redshifts (0.4 < z < 5). Therefore, I follow a second approach with the advantage of a
QSOsampleselectionatasingleredshiftepoch,decomposingtheevolutioneffectsfromthe
AGN/star-formation study. The results indicate that radio-jets in powerful QSOs can both
suppressandenhancethestarformationintheirhostgalaxies. Thesefundingsareconsistent
with a galaxy mass and jet-power dependence model. Then we expect more massivegalax-
ies to have more star-formation for a given jet-power because their star-formation is more
enhanced bythejet.
Although radio-jets are the best candidates for a direct AGN impact to the host galaxy,
many models refer to an AGN feedback associated with energetic AGN winds and outflows
which are expected to suppress the star formation in powerful AGN when compared to the
overallgalaxypopulation. Myresultsdonotsuggeststarformationissuppressedinthehosts
of optically selected QSOs at z 1, with more than 30 per cent of them being associated
≈
with strong star formation rates (SFR 350 M yr−1). Although different interpretations
⊙
≈
are possible, this result can be explained through periods of enhanced AGN activity and
star-formingbursts,possiblythroughmajormergers.
However, optical QSOs comprise only a small fraction of the total AGN population.
Even if the ‘unified model’ predicts that the host galaxy properties should not be affected
by the viewing angle (type-1 vs. type-2 AGN), several studies have shown results support-
ing a scenario departing from the basic model. Investigating star formation in the hosts of
24 µm selected type-1&2 AGN, I found that the type-2 AGNs display on average higher
v
star-formationratethantype-1AGNs. Thisresultisinagreementwithpreviousstudiessug-
gesting an undergoing transition between a hidden growth phase and an unobscured AGN
phase.
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... To my family!
Acknowledgements
Keeping a record of everyone who helped me during my PhD years seems challenging. So
first,Ihavetostartwiththeobvious... money! MoneymakestheworldgoroundandIwould
like to thank the University of Hertfordshire for providing me with a PhD scholarship to go
aroundtheworld.
As behind every PhD thesis there is a supervisor, my greatest regards go to Dr. Jason
Stevens. Dr. Stevenshas been a great mentor, always there to share with mehis experience,
comments,andworthwhileideas,yetallowingmetoworkindependently. WorkingwithDr.
Stevens,Ineverfelt likeaPhD student,butlikeaPhD researcher.
Additionally,IwouldliketothankProf. MattJarvisandProf. MartinHardcastleforshar-
ing their vast knowledgeon extragalacticastronomy, and collaboratingwith meon multiple
projects.
Movingfurther(andwhenIsayfurtherImeantotheUnitedStates),Iwouldliketothank
the advisers during my predoctoral at CfA - Dr. Martin Elvis and Dr. Francesca Civano.
WorkingatCfAwithDr. Elviswasanincredibleexperience-especiallyforsomeonestudy-
ingQSOs! Asexpected,eachandeverymeetingwithhimwaslikeloadingdozensofpapers
to your hard-drive. However, meetings with Martin would not have been so straightforward
withoutbeforefilteringmyinitialideaswithFrancesca. That’swhyIshouldthankFrancesca
forintroducingmetotheX-ray and Cambridgeworld when Ifirst movedthere.
But working at CfA was a great opportunity given to me by Dr. Markos Trichas. It all
started over seven years ago when I met Markos as my bachelor thesis advisor who turned
out to be a good friend and an even better career manager. Markos is responsible for many
of the opportunitiesthat have come my way in the last few years. Always there to share his
experienceandadvicemealthough,IthinkIcanhearhimrightnowcomplainingthatInever
listen...
Next,Iwouldliketothankmycolleaguesandfriendsduringtheseyears. Particularly,my
colleagues at UH with somespecial thanks to Hanifa for her amazing song! I want to thank
Gulay and Emrah, Dimitris and Maria (I should start worrying about spending time with
married couples). I have amazing memories with all of you, whether it be dinners, talking
about radio-jets and drinking beers, playing guitar, fighting about Greek yogurt, being such
great flatmates, or interruptingme whileworking for somemuch needed breaks. Movingto
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theothersideoftheAtlantic,IwanttosincerelythankthepeopleImettherethroughoutthis
great year; Valia(just for everything,my mum would be very proud for you) and the Italian
gang(E ora, con l’aiutodelsolevincero!).
But, whencolleaguesaretooprofessionalstocomplainaboutyourPhDand yourfamily
doesn’t knowwhat yourPhD is aboutwho shouldyou call? Eva! Apart from herfriendship
the last 15 years, the massive fun and the fights about politics she has always been there to
listen me complain about weird results, scripts that didn’t work, moving countries, moving
houses. If you ask her she would say that she knows everything about AGN... and I think
shemightdoes!
Finally, I would like to thank my family with a short story. My mum, as a math geek,
used to help me with my math courses at school. For this reason, every time I was getting
a good mark she used to say that half of that belonged to her. So, mum, dad, Stellaki and
grandma (my number one fan), half of this thesis definitely belongs to you. There are no
wordstoexpressmygratitude,so,IwillonlysaythatwithoutyouandyoursupportIwould
notbehere.
Thankyou all!
Contents
Abstract iii
Acknowledgements vii
ListofFigures xii
ListofTables xiv
ListofAbbreviations xv
Refereed Publications xvii
1 Introduction 1
1.1 TheGlobalPicture . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2
1.2 FindingAGN . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3
1.3 AGN Phenomenology . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
1.3.1 UnificationofAGN . . . . . . . . . . . . . . . . . . . . . . . . . . 7
1.3.2 Seyfert unificationscheme . . . . . . . . . . . . . . . . . . . . . . 9
1.3.3 Radio-loud– radio-quietAGN unification . . . . . . . . . . . . . . 11
1.4 AGN demographicsand evolution . . . . . . . . . . . . . . . . . . . . . . 14
1.5 ThehostgalaxiesofdistantAGNs . . . . . . . . . . . . . . . . . . . . . . 18
1.5.1 Where thedistantAGNslive? . . . . . . . . . . . . . . . . . . . . 22
1.5.2 Probing theAGN/Star-Formationconnection . . . . . . . . . . . . 23
1.6 LayoutofPhD Thesis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27
2 The largestX-ray-selected sampleofz > 3 AGNs: C-COSMOSandChaMP 28
2.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29
2.2 Sampleselection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30
2.2.1 TheC-COSMOS sample . . . . . . . . . . . . . . . . . . . . . . . 30
2.2.2 TheChaMPsample . . . . . . . . . . . . . . . . . . . . . . . . . . 33
2.3 TheC-COSMOS & ChaMPz > 3 AGN Sample . . . . . . . . . . . . . . . 39
2.3.1 OpticalTypes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 40
ix
CONTENTS x
2.3.2 X-ray Types . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 43
2.3.3 X-ray/Opticalflux ratio . . . . . . . . . . . . . . . . . . . . . . . . 44
2.3.4 Comparisonofopticaland X-ray types . . . . . . . . . . . . . . . 46
2.4 ThelogN-logS ofthez > 3 AGN . . . . . . . . . . . . . . . . . . . . . . . 48
2.5 2-10 keV Comovingspacedensity . . . . . . . . . . . . . . . . . . . . . . 53
2.5.1 Type-1 vsType-2 AGN . . . . . . . . . . . . . . . . . . . . . . . . 56
2.6 Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 57
3 Herschel-ATLAS: Far-infrared properties ofradio-loudandradio-quiet quasars 60
3.1 UnveilingtheroleofjetstotheAGN/star-formationconnection . . . . . . . 61
3.1.1 Radio-loudand radio-quietquasars . . . . . . . . . . . . . . . . . 63
3.1.2 Thiswork . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 64
3.2 Sampledefinitionand measurements . . . . . . . . . . . . . . . . . . . . . 64
3.2.1 Thedata . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 64
3.2.2 Herschelflux measurementsand stacked fluxes . . . . . . . . . . . 69
3.2.3 Luminositycalculation . . . . . . . . . . . . . . . . . . . . . . . . 70
3.3 Synchrotron contamination . . . . . . . . . . . . . . . . . . . . . . . . . . 71
3.4 Far-infrared properties . . . . . . . . . . . . . . . . . . . . . . . . . . . . 75
3.4.1 Stacking . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 76
3.4.2 FIR luminosity . . . . . . . . . . . . . . . . . . . . . . . . . . . . 80
3.4.3 Dusttemperatureand mass . . . . . . . . . . . . . . . . . . . . . . 80
3.4.4 250-µmluminosity . . . . . . . . . . . . . . . . . . . . . . . . . . 81
3.4.5 Two-Temperaturemodel . . . . . . . . . . . . . . . . . . . . . . . 83
3.4.6 Star-formation rate . . . . . . . . . . . . . . . . . . . . . . . . . . 84
3.5 Discussion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 87
3.5.1 Star-formation excess . . . . . . . . . . . . . . . . . . . . . . . . . 87
3.5.2 Hostgalaxyand dustproperties . . . . . . . . . . . . . . . . . . . 89
3.6 Conclusions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 90
4 The starformationrateofz 1 AGN 92
∼
4.1 Decouplingtheevolutioneffects . . . . . . . . . . . . . . . . . . . . . . . 93
4.2 Data . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 94
4.2.1 Sampleselection . . . . . . . . . . . . . . . . . . . . . . . . . . . 94
4.2.2 Herschel photometry . . . . . . . . . . . . . . . . . . . . . . . . . 97
4.2.3 SMA photometry . . . . . . . . . . . . . . . . . . . . . . . . . . . 98
4.3 Theblack holeand hostgalaxyproperties . . . . . . . . . . . . . . . . . . 102
4.3.1 Stellarmassand black holemass . . . . . . . . . . . . . . . . . . . 102
4.3.2 Accretion rate . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 104
4.3.3 FIR emissionin RLQs,RQQs and RGs . . . . . . . . . . . . . . . 105