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«¨ Munchen 2011 The XMM-BCS galaxy cluster survey ˇ ´ Robert Suhada Dissertation an der Fakult¨ t f¨ r Physik au der ...»

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The XMM-BCS galaxy cluster survey



Robert Suhada


Munchen 2011

The XMM-BCS galaxy cluster survey



Robert Suhada


an der Fakult¨ t f¨ r Physik


der Ludwig–Maximilians–Universit¨ t


M¨ nchen


vorgelegt von


R´ bert Suhada


aus Koˇice, Slowakei


M¨ nchen, den 25. M¨ rz 2011

u a

Erstgutachter: Prof. Dr. Hans B¨ hringer


Zweitgutachter: Prof. Dr. Ortwin Gerhard

Tag der m¨ ndlichen Pr¨ fung: 22. Juli 2011

u u Contents Zusammenfassung xiii


xv 1 Introduction 1 2 Clusters of galaxies 3

2.1 Dark matter content of galaxy clusters....................... 7

2.2 The intracluster medium.............................. 8 2.2.1 X-ray properties of clusters......................... 8 2.2.2 Spatial distribution of the cluster X-ray emission............. 10 2.2.3 Cool cores and AGN feedback....................... 12 2.2.4 X-ray scaling relations........................... 14 2.2.5 Self-similar scaling relations........................ 15 2.2.6 The Sunyaev-Zel’dovich effect....................... 17

2.3 The galaxy population of the clusters........................ 21 2.3.1 Brightest cluster galaxies.......................... 23 2.3.2 The cluster red sequence..............

–  –  –

Galaxienhaufen, SPT-CL J2332-5358 und SPT-CL J2342-5411, im R¨ ntgenlicht. Diese Haufen o wurden auch unabh¨ ngig durch ihr SZE Signal mit dem SPT und im optischen Band in den BCS a Daten erfasst. Sie sind damit die ersten Haufen, die unter Durchmusterungsbedingungen von allen drei großen Haufenidentifikazionsmethoden detektiert wurden. Diese Arbeit zeigt auch das Potenzial der Mosaik-Modus Beobachtungen große Himmelsbereiche effektiv abdecken zu k¨ nnen und massereiche Haufen bis zu Rotverschiebungen ∼ 1 auch mit kurzen Beobachtungo szeiten erfassen zu k¨ nnen.

o Der letzte Teil der Arbeit ist ein Beispiel f¨ r Multi-Wellenl¨ ngen-Analysen von Galaxienu a haufen mit hohen Rotverschiebungen (z 1) im Rahmen des XMM-Newton Distant ClusterProjekts. Mit der Entdeckung und dem Studium dieser hochrotverschobenen Galaxienhaufen beginnen wir, zum ersten Mal zu sehen, wie sich die heute komplett passive Population von Galaxien in Haufen bildet und wie bei den hohen Rotverschiebungen diese Galaxien immernoch deutliche Anzeichen von Sternbildung zeigen.

Abstract We are experiencing a unique epoch in the history of galaxy cluster studies. We have now open windows across the whole electromagnetic spectrum which offer us complementary approaches for cluster detection and analyses. Almost forty years after its theoretical prediction, first large radio telescopes started to scan the sky looking for massive clusters as ”shadows” in the cosmic microwave background imprinted there by their hot gas content via the Sunyaev-Zel’dovich effect (SZE). In X-rays this hot plasma can be observed also directly. Optical and infrared telescopes give us a view on the galaxy population of clusters and through gravitational lensing also on its dominant, invisible component - the dark matter.

The advent of multi-wavelength cluster surveys brings also the necessity to compare and cross-calibrate each cluster detection approach. This is the main aim of this work carried out in the framework of the XMM-Newton-Blanco Cosmology Survey project (XMM-BCS). This project is a coordinated multi-wavelength survey in a 14 deg2 test region covered in the optical band by the Blanco Cosmology Survey, in the mid-infrared by the Spitzer Space Telescope and in X-rays by XMM-Newton. This area is also part of the sky scanned by both SZE survey instruments: the South Pole Telescope (SPT) and the Atacama Cosmology Telescope (ACT).

In the first part of the thesis I describe the analysis of the initial 6 deg2 core of the X-ray survey field. From the detected extended sources a cluster catalog comprising 46 objects is constructed. These cluster candidates are confirmed as significant galaxy overdensities in the optical data, their photometric redshifts are measured and for a subsample confirmed with spectroscopic measurements. I provide physical parameters of the clusters derived from X-ray luminosity and carry out a first comparison with optical studies. The cluster catalog will be useful for direct cross-comparison with optical/mid-infrared catalogs, for the investigation of the survey selection functions, stacking analysis of the SZE signal and for cosmological analyses after combing with clusters detected in the extension of the survey.

The extension of the survey to 14 deg2 is a first scientific utilization of the novel XMMNewton mosaic mode observations. I have developed a data analysis pipeline for this operation mode and report on the discovery of two galaxy clusters, SPT-CL J2332-5358 and SPTCL J2342-5411, in X-rays. The clusters were also independently detected through their SZE signal by the SPT and in the optical band in the BCS data. They are thus the first clusters detected under survey conditions by all major cluster search approaches. This work also demonstrates the potential of the mosaic mode observations to effectively cover large sky areas and detect massive clusters out to redshifts ∼ 1 even with shallow exposures.

The last part of the thesis provides an example of a multi-wavelength analysis of two highxvi Abstract

redshift (z 1) systems in the framework of the XMM-Newton Distant Cluster Project. With the detection and studies of these high redshift systems we are for the first time able to see the assembly phase of the galaxy population of the clusters, which in nearby systems is totally passive, but at these high redshifts still show signatures of star formation.

Chapter 1


Multi-wavelength surveys give us a comprehensive look at the population of galaxy clusters and groups in the Universe. They allow us to study cluster evolution in the full relevant redshift range, from the nearby Universe out to redshift of z = 1 and beyond. We can also access the full mass range spanning from 1013 M⊙ (the group regime) to ∼ 1015 M⊙ (most massive clusters). Observations in different parts of the electromagnetic spectrum offer us outlook on the individual cluster components: the galaxy population from UV through optical to infrared bands, the intracluster medium (ICM) in X-rays and via the Sunyaev-Zel’dovich effect (SZE) and also the dark matter (indirectly through gravitational lensing). The multi-wavelength approach thus brings about many synergies: e.g. X-ray and SZE studies give us a way to safely detect clusters, study their thermodynamical evolution and provide good precision estimates of the total mass, while optical observations then can establish the redshifts of the systems and investigate the processes shaping their galaxy populations.

Cluster studies are, however, not motivated only by astrophysical interests, but are also part of cosmological investigations. The mass distribution of the cluster population and its evolution with redshift are very sensitive to the cosmological parameters and allow us to constraint not only the parameters describing the matter content of the Universe (baryonic and dark matter), but ultimately shed light on its most enigmatic component - the Dark Energy.

In order to access the full potential of such studies, we need to answer several important questions. Firstly, what are the selection functions of these surveys, what kind of systems are they sensitive to and why do they miss others? Since each surveying approach probes clusters and groups in a different way it is not surprising that they will be more sensitive to different parts of the cluster population and have different systematics. Simulations can give us estimates of their selection functions, but comparing cluster samples extracted from a common test field is crucial to gain full understanding of these surveying methods. Secondly, the total cluster mass is the most important physical parameter of the cluster, but from observations it is accessible only indirectly through scaling relations from an observable parameter. Construction of good (unbiased and low scatter) mass scaling relations is crucial for future applications of cluster surveys. A multi-wavelength cross-comparison can again test the assumptions and selection effects of each approach and thus help to pave the way for future large surveys.

Most of the present work has been done in the framework of the XMM-BCS project. This

2 1. Introduction

project tries to answer these questions by combining optical, mid-infrared and X-ray observations in a single test field covered also by the SZE surveys conducted by the South Pole Telescope and Atacama Cosmology Telescope. This project is introduced in detail in Chapters 4 and 5, where we describe our first results.

Before that, however, we provide three introductory chapters that give an overview of the basic concepts relevant for studies presented in this work. Chapter 2 contains a concise introduction to clusters of galaxies, their main components and relevant undergoing physical processes.

We also highlight the observational signatures of clusters and discuss their detection in the main surveying approaches. The cosmological perspective of the clusters is reviewed in Chapter 3. We describe the evolution of clusters within the large-scale structure of the Universe and how this can be related to the background cosmology. We also discuss how the survey selection function enters this kind of studies.

The data analysed in the course of this work were obtained with the XMM-Newton X-ray telescope. Therefore, we describe this instrument in Chapter 4, where we also provide an introduction to the basic concepts of X-ray imaging. The chapter closes with a detailed description of the mosaic mode observations by XMM-Newton. The material covered here also comprises technical descriptions of analysis recipes for this new type of data developed during this thesis’ work.

The next three chapters collect research papers from the XMM-BCS cluster survey and the XMM-Newton Distant Cluster Project (XDCP). In Chapters 5 we provide first results from the 6 deg2 core region of the XMM-BCS survey. We construct here a catalog of 46 X-ray selected clusters and groups of galaxies. We provide for them photometric redshift estimates and physical parameters determined from their X-ray luminosities. The photometric redshifts are confirmed for a subsample of clusters with spectroscopic measurements and a first comparison with optical mass estimates is carried out. We provide extensive test of our X-ray analysis pipeline and give an outlook on the ongoing studies based on this cluster catalog. Chapter 6 introduces the 8 deg2 extension of the survey and provides the analysis of two very massive X-ray selected clusters, one at low- and the second at high redshift. These systems were also independently detected through their SZE signature by the South Pole Telescope and are thus the first systems to be found by all major cluster search methods in survey conditions. We find good agreement between the X-ray and SZE estimated properties of these clusters.

In Chapter 7 we provide the analysis of two high redshift (z 1) systems detected in X-rays by the XDCP survey. We confirm one of these to be a bona fide cluster at redshift z = 1.185. We provide its physical properties and investigate the galaxy population which shows signs of ongoing star formation in many of its members. For the second system we find the X-ray detection to be coincident with a dynamically bound galaxy system at z = 1.358. Optical spectroscopy, however, reveals the presence of a central active galactic nucleus, which can be a dominant source of the detected X-ray emission from this system. We discuss cluster identification challenges in the high-redshift, low-mass cluster regime and provide upper limits on X-ray parameters for this system.

We summarize the main results of the thesis in the closing Chapter 8 and provide conclusions and outlook on future work for these projects.

Chapter 2

Clusters of galaxies

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