Fakultät für Physik - Digitale Hochschulschriften der LMU - Teil 03/05

Despite being a minority among the total population of galaxies, radio galaxies have gained increasing attention, because of the energetic feedback they can provide to the surrounding environment. These systems host an active nucleus that produces large amounts of energy in the form of radio/X-ray emitting jets, injecting energy that in some cases can balance the radiative loses of the gas that cools and condenses within massive halos of dark matter. Therefore, if we want to understand galaxy formation and evolution, we have to understand the role of active galactic nuclei (AGN) in the galaxy assembly process.

My work concentrated, first, on constructing a complete sample of radio galaxies. This is not an easy task as they have very different morphologies in different surveys, and ofter break up into separate components. These components must be correctly associated with a unique optical galaxy. We cross-correlated two different radio surveys (NVSS and FIRST) with a sample of luminous red galaxies derived from the Sloan Digital Sky Survey (SDSS). The NVSS provides accurate flux measurements for extended sources, while the angular resolution of FIRST allows the host galaxy to be identified accurately. We also improved the matching of sources below the nominal 1 mJy detection limit of FIRST, to increase the reliability and completeness of the final catalogue. These techniques allowed us to assemble the

largest radio galaxy catalogue to date, consisting of around 14,000 radio–loud AGN at intermediate redshifts (0.4 < z < 0.8), with 1.4 GHz fluxes above 3.5 mJy. The matching criteria were tested and refined using Monte–Carlo simulations, leading to an estimated reliability of ∼98.3% and completeness level of about 95% for our catalogue.

With this catalog in hand, we were able to compare radio galaxies at z∼0.55 with similar samples in the local universe. We studied the evolutionary properties of radio galaxies, how their spatial density changes as function of time and how the fraction of radio emitting sources varies with galaxies properties such as stellar mass, radio luminosity and redshift. We present a new determination of the luminosity function of radio AGN at z∼0.55 and compare this to the luminosity function of nearby (z∼0.1) radio sources from the SDSS main survey. The comoving number density of radio AGN with luminosities less than 10^25 W/Hz

increases by a factor ∼1.5 between z=0.1 and z=0.55. At higher luminosities, this factor increases sharply, reaching values of more than 10 at radio luminosities

larger than 10^26 W/Hz. We then study how the relation between radio AGN and their host galaxies evolves with redshift. Our main conclusion is that the fraction of radio–loud AGN increases towards higher redshift in all massive galaxies, but the evolution is particularly strong for the lower mass galaxies in our sample. These trends may be understood if there are two classes of radio galaxies (likely associated with the “radio” and “quasar mode” dichotomy) that have different fuelling/triggering mechanisms and hence evolve in different ways. We conclude that stellar mass seems to be the a very important factor in deciding whether a galaxy develops bright, powerful radio jets.

There is also the suggestion that the environment of a galaxy is also crucial in deciding whether it becomes radio-loud. To address this question, we studied how radio galaxies are clustered in the universe and quantified the clustering dependence on stellar mass and radio power. We do this by computing the cross-correlation function between radio galaxies and the parent LRG population. In order to isolate the true clustering of RLAGN, we compare respect to control radio-quiet galaxies selected with the same properties as radio AGN. The main result is that RLAGN are significantly more clustered than radio-quiet objects, particularly below ∼1 Mpc/h, indicating that the gaseous environment of a radio sources at the scale of its dark matter halo is import

The cosmic microwave background (CMB) provides us with a wealth of information about the properties of our Universe. In this PhD work, we develop and apply new techniques for studying fundamental problems of cosmology using the CMB.

Dark energy, if it exists, leaves a characteristic imprint in the CMB temperature fluctuations, the so-called integrated Sachs-Wolfe (ISW) effect. This small effect can be detected via its cross-correlation with the large-scale structure (LSS). We derive an optimal method for ISW detection using temperature and polarization data of the CMB which differs from that usually used in two fundamental ways: we keep the LSS distribution and a part of the

primordial temperature fluctuations fixed, rather than averaging over different realisations as done in the standard method. For an ideal scenario, we obtain an overall enhancement of the detection significance of 23 per cent. For polarization data from the Planck Surveyor mission, this enhancement will be at least 10 per cent, where the limiting factor will be the contamination by Galactic foregrounds.

The CMB is observed to be almost perfectly isotropic, which is considered strong evidence for the isotropy of the

Universe. However, some anomalies have been found in the

temperature map of the Wilkinson Microwave Anisotropy Probe

(WMAP), which seem to question the statistical isotropy of the temperature fluctuations. In order to understand

whether these are due to chance fluctuations or to a preferred direction intrinsic to the geometry of the primordial Universe, we compute the part of the WMAP

polarization map which is uncorrelated with the temperature map, and use it as a statistically independent probe of the so-called axis of evil. The latter is an unusual alignment between the preferred directions of the quadrupole and the octopole in the temperature map. We find that the axis of the quadrupole of the uncorrelated polarization map aligns with the axis of evil, whereas the axis of the octopole does not. However, due to the high noise-level in the WMAP polarization map, we have an uncertainty of about 45 deg in our axes. With this uncertainty, the probability of at least one axis aligning by chance in an isotropic Universe is around 50 per cent. We therefore do not obtain evidence for or against a preferred direction intrinsic to the primordial Universe. For Planck, we expect the uncertainty in the axes to go down to 10-20 deg, again depending on how well the foregrounds can be removed from the map. Our technique applied to Planck data will thus serve as a powerful means to understand the origin of the CMB anomalies.

Instead of studying particular features in the CMB maps as

described above, we can also use the CMB to constrain

several cosmological parameters simultaneously by sampling the parameter space. The parameter constraints obtained by WMAP marked the beginning of precision cosmology and were the biggest success of the mission. In such parameter sampling studies, the main bottleneck is usually the evaluation of the likelihood. We have thus implemented a sparse-grids based interpolation of the WMAP likelihood surface as a shortcut for the likelihood evaluation. This

is orders of magnitude faster to compute than the original likelihood. Our method is a competitive alternative to other approaches for speeding up parameter sampling.

Die Entwicklung des ersten präzisen kosmologischen Modells, des LCDM Modells, ist eine bedeutende Errungenschaft der modernen, beobachtenden Kosmologie. Trotzdem bleiben eine Reihe von wichtigen Fragen über Zusammensetzung und Entwicklungsgeschichte des Universums unbeantwortet: Abgesehen von der Natur der Dunklen Materie ist der physikalische Ursprung der Dunklen Energie eine der ganz großen Fragen der theoretischen Physik. Ebenso bedürfen die statistischen Eigenschaften der anfänglichen Dichtefluktuationen im frühen Universum einer genauen überprüfung. Kleinste Abweichungen von den

Gauß'schen Fluktuationen des Standardmodells würden, sofern sie nachgewiesen werden, eine Vielzahl von Informationen über die Physik des frühen Universums enthalten. In dieser Arbeit benutze ich numerische Verfahren, um neue, hochpräzise Vorhersagen zur kosmischen Strukturbildung in generalisierten Dunkle Energie Kosmologien zu treffen. Außerdem berücksichtige ich Modelle mit nicht-Gauß'schen

Anfangbedingungen. Im ersten Abschnitt untersuche ich die nicht-lineare Strukturentstehung in sogenannten `Early Dark Energy' (EDE) Modellen und vergleiche sie mit dem LCDM Standardmodell. Interessanterweise zeigen meine Ergebnisse,

dass der Sheth and Tormen (1999) Formalismus, mit dem üblicherweise die Anzahldichte von Halos aus Dunkler Materie geschätzt wird, in EDE Kosmologien weiterhin anwendbar ist, im Widerspruch zu analytischen Berechnungen. In diesem Zusammenhang untersuche ich auch das Verhältnis zwischen Masse und Geschwindigkeitsdispersion der Dunklen Materie in Halos. Dabei stelle ich eine gute

übereinstimmung mit der Normalisierung der LCDM Kosmologien

fest, wie sie in Evrard et al. (2008) beschrieben ist. Allerdings führt das frühere Anwachsen der Dichtestrukturen in EDE Modellen zu großen Unterschieden in der Massenfunktion der Halos bei hohen Rotverschiebungen. Dies könnte direkt in Beobachtungen gemessen werden, indem man die Anzahl der Gruppen als Funktion der Geschwindigkeitsdispersion der enthaltenen Galaxien entlang der Sichtlinie bestimmt. Insbesondere würde dadurch das Problem der mehrdeutigen Massebestimmung von Halos umgangen. Schließlich ermittele ich die Beziehung zwischen dem Konzentrationsparameter von Halos und der Halomasse in den EDE Kosmologien.

Im zweiten Teil meiner Arbeit verwende ich ein Set an hochaufgelöste hydrodynamische Simulationen um die

globalen Eigenschaften der thermischen und kinetischen Sunyaev Zeldovich (SZ) Effekte zu untersuchen. Dabei stellen wir fest, dass in den SZ-Beobachtungskarten der EDE Modelle der Compton-y-Parameter systematisch größer

ist als im LCDM Modell. Erwartungsgemäß finde ich daher

auch, dass das Leistungsspektrum der thermischen und kinetischen SZ Fluktuationen in EDE Kosmologien größer ist als im Standardmodell. Allerdings reicht diese Steigerung für realistische EDE Modelle nicht aus, um die theoretischen Voraussagen in übereinstimmung mit aktuellen Messungen der Mikrowellenhintergrundanisotropie bei großen Multipolwerten zu bringen. Eine Zählung der durch den SZ Effekt detektierbaren Halos in den simulierten Karten zeigt nur einen leichten Anstieg in den massereichsten Haufen für EDE Kosmologien. Ebenso sind Voraussagen für

zukünftige Zählungen von SZ-detektierten Haufen durch das South Pole Telescope (SPT Ruhl, 2004) stark durch Unsicherheiten in der Kosmologie beeinträchtigt. Schließlich finde ich, dass die Normalisierung und die Steigung der Relation zwischen thermischem SZ-Effekt und Halomasse in vielen EDE Kosmologien unverändert bleibt, was die Interpretation von Beobachtungen des SZ Effekts in Galaxienhaufen vereinfacht.

In weiteren Untersuchungen berechne ich eine Reihe von hochaufgelösten Vielteilchensimulationen für physikalisch motivierte nicht-Gauß'sche Kosmologien. In umfangreichen

Studien untersuche ich die Massenverteilungsfunktion der Halos und deren Entwicklung in nicht-Gauß'schen Modellen. Zudem vergleiche ich meine numerischen Experimente mit analytischen Vorhe

In this thesis we study the dynamics of social systems and molecular monolayers employing tools of statistical physics. In both cases the topological structure underlying the interactions turns out to be the key element in the emergence of collective macroscopic phenomena from the synergy of the individual interactions.