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Observations and Models of High Redshift Radio Galaxies and Quasars from the 3Rd Cambridge Catalog”

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Observations and Models of High Redshift Radio Galaxies and Quasars from the 3Rd Cambridge Catalog” ”Observations and models of high redshift Radio Galaxies and Quasars from the 3rd Cambridge catalog” Dissertation zur Erlangung des Grades ”Doktor der Naturwissenschaften” an der Fakultat¨ fur¨ Physik und Astronomie der Ruhr-Universitat¨ Bochum von Frank Heymann aus Leipzig Bochum 2010 b.w. 2 1. Gutachter Prof. Dr. Rolf Chini 2. Gutachter Priv.-Doz. Dr. Dominik Bomans Datum der Disputation 05.07.2010 3 Abstract This thesis provides new observations of the most powerful high redshift Active Galactic Nuclei (AGN), namely the complete z > 1 3CR sample, and new dust radiative transfer modeling of their measured spectral energy distribution in the infrared. This work is separated into three main parts, two observational sections and one section containing the modeling. The first part shows observational results in the near (NIR) and mid (MIR) infrared obtained with the Spitzer Space Telescope, to extend the knowledge on high redshift sources. The main aspect of these observations is to study orien- tation dependence of the NIR and MIR emission and to confirm the unification scheme for the most powerful high redshift AGNs. The second part reports on a pilot study to detect galaxy clustering around high redshift radio sources using the Spitzer data. Because the radio AGN reside in massive host galaxies, they are expected to serve as signposts for cosmic mass peaks. These galaxy clusters are among the most distant known structures and therefore of particular cosmological interest. The third part explains a newly developed method to solve the radiative trans- fer equation in three dimensional configurations. This method makes use of the parallelization capabilities of modern vector computing units, like the graphics cards. The speed improvement is about a factor of 100. This enables us to model the close environment of AGN in so far unprecedented detail within reasonable computing time. 4 Contents 1 Introduction 7 1.1 Aimofthisthesis........................... 7 1.2 ActiveGalacticNuclei ........................ 7 1.2.1 Seyfert Galaxies . 9 1.2.2 Quasars & Radio Galaxies . 10 1.2.3 Unification........................... 10 1.3 GalaxyClustering........................... 11 1.4 Dustradiation............................. 12 1.4.1 Theemissivityofdust . 13 1.4.2 Thetemperatureofbiggrains . 13 1.4.3 Verysmallgrains ....................... 14 1.5 BasicRadiativetransport . 15 1.5.1 Definitions........................... 15 1.5.2 The general transfer equation . 16 1.5.3 Analytical solutions . 17 2 Near- and mid infrared photometry 19 2.1 Motivation............................... 20 2.2 ObservationsandData . 21 2.3 ResultsandDiscussion ........................ 24 2.3.1 Radio galaxies as obscured quasars . 24 2.3.2 Evolutionary effects and non-thermal contributions . 27 2.4 Conclusions .............................. 28 3 The cluster search 35 3.1 Motivation............................... 35 5 6 CONTENTS 3.2 Clusteringaround3C270.1 . 37 3.2.1 Observationsanddata . 37 3.2.2 Results............................. 38 3.3 No evidence for clustering around 3C 437 . 51 3.3.1 Observationsanddata . 51 3.3.2 Results............................. 51 3.3.3 Preliminary Conclusion . 53 4 Parallel 3D radiative transport 55 4.1 Theory................................. 55 4.1.1 MonteCarlomethod . 55 4.1.2 Parallelization . 58 4.1.3 Pseudo random number generator in parallel . 60 TM 4.1.4 CUDA parallelization on graphic cards . 60 4.2 Imaging ................................ 61 4.2.1 Solarsystem.......................... 65 4.3 Benchmarktest ............................ 65 4.3.1 Sphericalsymmetry(1D). 65 4.3.2 Diskgeometry(2D). 67 4.3.3 Dustproperties ........................ 69 4.3.4 Spiral expansion of disk structure (3D) . 69 4.3.5 Clumpy Torus geometry (3D) . 70 4.4 Modelingaveragespectra&SEDs. 75 5 Summary and Outlook 81 Bibliography 87 List of Figures 93 List of Acronyms 101 Chapter 1 Introduction 1.1 Aim of this thesis At the begin of my thesis, new unprecedented infrared observations of the com- plete high-redshift 3CR sample have been obtained with the Spitzer Space Tele- scope. Therefore, the aim of this thesis is • to explore the near- and mid-infrared spectral energy distributions of this sample, comprising the most powerful radio-loud AGN, • to test, how far it is possible with these data to detect galaxy clustering around these mass peaks of the early universe, • and to develop a new proper 3D Monte Carlo radiative transfer code to model the spectral energy distributions. These three tasks represent new challenges and thus lead to new results. 1.2 Active Galactic Nuclei Active Galactic Nuclei (AGN) belong to the the most luminous objects in the universe. The luminosity of an AGN is provided by accretion of matter onto the central supermassive black hole: ˙ ˙ 2 12 ǫ M LAGN = ǫ M c ≈ 1.2 10 L⊙ , (1.1) 0.1 M⊙/yr where ǫ is the efficiency of the mass to radiative energy transfer, L⊙ solar lu- minosity, M⊙ solar mass and M˙ the mass accretion. This leads to a theoretical 7 8 1.2. ACTIVE GALACTIC NUCLEI upper limit for the central luminosity, named after Arthur Stanley Eddington: 4πGMBH mpc 11 MBH Lmax <LEdd = ≈ 3.27 10 L⊙ 7 , (1.2) σT 10 M⊙ where mp is the mass of the proton, σT the Thomson cross section for interaction between electrons and protons. The wavelength spectral energy distribution of an AGN exhibits three characteristic features (Elvis et al. 1994) as shown in Fig 1.2: Figure 1.1: Sketch of an AGN continuum spectrum of the nuclear region, without stellar contribution. Three different bumps can be seen (Big Blue Bump in the middle, Infrared Bump on the left and X-ray ’Bump’ on the right). Figure from Manners (2002) • Infrared Bump This feature consists of several components. Dominant is the emission from the hot and warm dust torus (red dashed line) and cooler dust from the host galaxy. The starburst activity in the host galaxy contributes to the far infrared (purple dotted line) followed by a steep decrease of the Infrared bump to the submillimeter (Chini et al. 1989). The local minimum at around 1µm is given by the sublimation temperature of the dust around ∼ 1500 K. CHAPTER 1. INTRODUCTION 9 • Big Blue Bump At shorter waverlengths the minimum turns into the Big Blue Bump (blue dashed-tripple-dotted line). This bump comes from the thermal emission of hot gas (5 000K − 100 000 K) heated by viscous processes, in the accretion disk. The gap in the bump results from absorption of neutral hydrogen and therefore missing data. This optical/UV radiation is efficiently transfered into infrared emission and therefore powers the Infrared Bump. (Miley et al. 1985) • X-ray ’Bump’ The final feature in the AGN continuum is the high energy X-ray ’Bump’. The radiation in this bump is produced by the hot corona above the accre- tion disk (green dashed line) and reflection of the disk (blue dashed-dotted line). The observational data of my thesis provide new constraints on the Infrared Bump (chapter 2), and the model part makes use of all three bumps (chapter 4). 1.2.1 Seyfert Galaxies These galaxies, discovered by Seyfert (1943), contain a bright nucleus with strong emission lines from highly ionised gas (hydrogen, helium, nitrogen, oxygen). The Seyfert galaxies can be divided into two subclasses depending on the existence of broad and narrow emission lines (type 1) or only narrow lines (type 2) (Khachikian & Weedman 1974). The broad lines have velocities of 1 500−10 000 km s−1, may vary on short timescales and can be explained by Doppler broadening. These high velocities can be explained by gas clouds, orbiting the black hole at small distances. It is also possible that these lines are emitted from the accretion disc itself. However due to the extremly high resolution which is neccessary to resolve the innermost part, it is difficult to observe the exact geometry of these objects. The narrow emission lines may by emitted by gas clouds further out. This is strengthened by the fact that the narrow lines are detected in all types of Seyfert galaxies, which implies that the emitting region is large. Breakthrough spectropolarimetric observations revealed, that some Seyfert 2 galaxies contain a hidden broad line region, leading to the AGN unification scheme (section 1.2.3). 10 1.2. ACTIVE GALACTIC NUCLEI 1.2.2 Quasars & Radio Galaxies These two object classes are the powerful radio-loud cousins of the Seyfert galax- ies. On early optical images quasars appeared starlike, which gave these objects the name quasi stellar radio source. In quasars and radio galaxies large struc- tures, the radio lobes, are prominent. Depending on the morphology and power of the radio lobes, the radio sources are subdivided into the FR I and FR II classes (Fanaroff & Riley 1974). We here consider only the edge-brightened pow- erful FR II sources. The radio emission is powered by synchrotron radiation of outflowing material reaching 95% of the speed of light. Assuming an accretion disc and perpendicular to this disc an outflowing jet producing the synchrotron radiation, it is possible to explain these two objects with the orientation of the jet to the line of sight. The quasars, where the jet points to the observer, repre- sent the type 1 AGN and the Radio Galaxies, where the jet is perpendicular to the line of sight, can be classified as type 2 (Barthel 1989; Orr & Browne 1982). The isotropic radiation at meter wavelengths enables to select objects with the same radio power and to study orientation dependent effects. While for the local universe (z < 1) orientation dependencies are fairly well studied, the knowledge is poor at high redshift (z > 1). 1.2.3 Unification Figure 1.2 shows the actual picture of the unification model. It is believed that Type 1 and Type 2 galaxies are in essence the same, and they differ only by the angle at which they are observed.
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