Observations of the Sunyaev-Zel'dovich effect towards clusters of galaxies with the APEX telescope [Elektronische Ressource] / vorgelegt von Martin Nord

Martin Nord

Sujets

• Astronomie

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• Publié par: rheinische_friedrich-wilhelms-universitat_bonn
• Publié le: 01 janvier 2009
• Nombre de lectures: 14
• Langue: English
• Poids de l'ouvrage: 8 Mo

Extrait

Observations of the Sunyaev-Zel’dovich
Effect towards Clusters of Galaxies
with the APEX Telescope
Dissertation
zur
Erlangung des Doktorgrades (Dr. rer. nat.)
der
Mathematisch-Naturwissenschaftlichen Fakult¨at
der
Rheinischen Friedrich-Wilhelms-Universit¨at Bonn
vorgelegt von
Martin Nord
aus
Helsingborg, Schweden
Bonn, 2009Angefertigt mit Genehmigung
der Mathematisch-Naturwissenschaftlichen Fakult¨at
der Rheinischen Friedrich-Wilhelms-Universita¨t Bonn
1. Gutachter: Prof. Dr. Frank Bertoldi
2. Gutachter: Prof. Dr. Karl Menten
Tag der Mu¨ndlichen Pru¨fung: 21. August 2009
Erscheinungsjahr: 2009Abstract
Results of 150 GHz continuum observations of several X-ray bright clusters of galaxies in
the Sunyaev-Zel’dovich (SZ) effect, carried out using the APEX-SZ bolometer array on the
APEX telescope, are presented. Follow-up observations of the cluster A2163 with the Large
APEX Bolometer Camera (LABOCA) at 345 GHz on the same telescope have been carried
out, yielding the largest map of a cluster of galaxies in the SZ increment to date.
DetailsofpossiblecontaminantsaffectingtheSZsignalareoutlined,andasimulatedgalaxy
cluster survey is used to estimate levels of contamination from each source of emission. In
agreement with previous studies it is found that primary CMB anisotropies are a weak source
of contamination for SZ observations of distant clusters, although massive nearby clusters can
be severely contaminated. Radio point sources are found to be of possible concern, but more
informationonspectralslopesinthemillimeterregimeisneededbeforeanydecisiveconclusions
can be made. It is found that treating unresolved thermal sources as a source of excess noise
yields an excellent approximation of this contaminant, which sets a fundamental confusion
limit on single-frequency SZ measurements.
The 1.4 GHz volume averaged radio source luminosity function is constructed from a large
sample of galaxy clusters. In contrast to previous studies, an adaptive cluster volume is used
to construct the luminosity function. This is shown to yield more robust results on volume
averagedsourcecounts, and for the firsttime a redshift evolution in this luminosity function is
found, taking into account the variable effect on radio source confusion with redshift. Due to
thelargesamplesize,luminosityevolutionandnumberdensityevolutioncanbeseparated,and
3.3±1.2it is found that the average luminosity scales with the redshift parameter z as (1+z) ,
2.8±0.9and the number density as (1+z) .
The APEX-SZ and LABOCA instruments are described from an observer’s perspective.
The analyses of pointing and calibration data are described, and the data quality of each
instrument is assessed. The reduction of galaxy cluster data is described in detail, including
the steps of time stream reduction, involving the removal of correlated atmospheric noise, and
mapping. Losses in source brightness due to the removal of correlated noise are modeled with
a transfer function based on the reduction of a point source convolved with the instrument
beam. It is shown that this approachis valid for a wide rangeof source morphologiesprovided
the reduction is done within a set of certain well-defined steps.
Significant detections of 9 clusters of galaxies with APEX-SZ are presented. The clusters
are modeled using the well-known isothermal β model, which proves to be sufficient in most
cases due to the relatively low significance compared to state-of-the-art X-ray measurements.
TheSZsignalsarefoundtobeinoverallagreementwithpredictionsfromX-raymeasurements.
As expected, the isothermal pressure profiles from the SZ measurements are broader than the
surface brightness profiles from X-ray experiments.
The possibility of simultaneously extracting gas temperatures and bulk velocities from SZ
measurements is briefly discussed. It is found that current data have poor leverage on the
iproblem; reasonable constraints require accurate measurements both at high frequencies (&
300 GHz), where confusion due to dust emission becomes increasingly more of a problem, and
at low frequencies (. 90 GHz), where radio point sources can contaminate the signal.
A non-isothermal model of the galaxy cluster A2163 is presented, based on APEX-SZ and
XMM-Newton X-ray data. Under the assumption of spherical symmetry, the two data sets
are used to de-project the structure of the cluster in terms of temperature and density, and
the results are used to derive the gas mass profile. The total mass profile is derived under
the assumption of hydrostatic equilibrium, to allow for an estimate of the gas mass fraction.
It is shown that the isothermal approximation well approximates the non-isothermal model
inside the X-raycoreradius, where the mean gastemperature derived fromthe SZ/X-rayjoint
analysisis9.6±0.3keV.Themassprofilefromthenon-isothermalanalysisisinagreementwith
weak lensing measurements. The APEX-SZ data is also used, in conjunction with LABOCA
dataat345GHzandpreviouslypublishedSZdataatotherfrequencies,toconstrainthecentral
Comptonization and bulk velocity of the cluster, using priors on the temperature of the intra-
cluster gas. A line-of-sight peculiar velocity of−140±460km/s and a central Comptonization
−4of (3.42±0.32)×10 are found for Abell 2163.
iiAcknowledgments
ThisPhDthesiswascompletedattheArgelander-Institutfu¨rAstronomieinBonn. Duringthe
first three years of my graduate studies I was supported by a stipend from the International
MaxPlanckResearchSchool(IMPRS)forRadioandInfraredAstronomyattheUniversitiesof
BonnandCologne,whileduringthelast10monthsIwassupportedbyastipendfromtheUni-
versity of Bonn. Proprietary data used in this thesis come from the APEX-SZ and LABOCA
bolometer arrays on the APEX telescope, a collaboration between the Max-Planck-Institut
fu¨r Radioastronomie,the EuropeanSouthern Observatory,and the OnsalaSpace Observatory.
APEX-SZisfundedbytheNationalScienceFoundation(USA)underGrantNo. AST-0138348.
Parts of the work presented here have been developed in collaboration with others. In
particular, much of the research laid out in chapters 4 and 9 has been conducted in close
collaborationwithKaustuvBasu. Muchofthematerialinchapters5and6hasbeeninspiredby
discussionswith othermembersofthe APEX-SZcollaboration(toonumeroustolist) although
it reflects solely my own work where not explicitly stated otherwise.
I am grateful to my supervisor,Frank Bertoldi, and to my second referee, KarlMenten, for
their support during my time as a graduate student at AIfA. I have had the great fortune of
sharing an office with my friend and colleague Kaustuv Basu, who has often been my de facto
thesis advisor. It is no exaggeration to state that this thesis, in its present form, would not
havebeen possiblewithout him. Thanksalsoto Axel Weiss for providingcalibrationtables for
345 GHz continuum observationsand to Fred Schuller for helping with LABOCA data taking.
On the administrative side of things, I am grateful to Christina Stein-Schmitz, Gabi Breuer
and Eduardo Ros.
I am much indebted to those who have taken the time to comment on the draft of this
thesis (or parts thereof), in particular Frank Bertoldi, Karl Menten, Kaustuv Basu, Kirsten
Kraiberg Knudsen and Cathy Horellou. Scientific as well as extra-curricular discussions with
my old friend Daniel Johansson are likewise gratefully acknowledged.
I would like to thank Manuel (“P˚agen”) Aravena for many enjoyable sessions in the AIfA
“beer cellar”, for discussions in the coffee room, covering a wide dynamic range of serious-
ness, and for other things too numerous (or inappropriate) to mention. I shall never forget
Klagenfurt. IthankAlexandreBeelenforpatientlyintroducingmetobolometerarraydatare-
duction, for teaching me the correct pronunciation of pardon, and for sharing countless rounds
of Weissbier with me in the “Biergarten”. Il existe pr`es des ´ecluses.
iiiI don’t think I would have survived without my family. Lena and Anni-Lotta, thanks for
putting up with and supportingasometimes grumpyboyfriendandfather. You areboth more
important than galaxies, even whole clusters of them. I am deeply grateful to my parents,
Karin and G¨oran, for always having encouraged me to pursue my interests. I would not have
been here (or anywhere else) without you.
Bonn, May 2009 Martin Nord
ivContents
1 Introduction 1
2 Clusters of Galaxies and the Sunyaev-Zel’dovich Effect 5
2.1 Clusters of Galaxies and the Intra-Cluster Medium . . . . . . . . . . . . . . . . 5
2.1.1 Definition . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
2.1.2 Origin . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
2.1.3 Mass . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
2.1.4 Temperature . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
2.1.5 Optical and Infrared Observations . . . . . . . . . . . . . . . . . . . . . 7
2.1.6 X-ray Observations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8
2.2 The Sunyaev-Zel’dovich Effect. . . . . . . . . . . . . . . . . . . . . . . . . . . . 8
2.2.1 The Diffusion Approximation . . . . . . . . . . . . . . . . . . . . . . . . 8
2.2.2 Temperature and Received Power. . . . . . . . . . . . . . . . . . . . . . 10
2.2.3 The Relativistic Thermal Equation . . . . . . . . . . . . . .