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

In der vorliegenden Arbeit werden isolierte, einzeln ortsaufgelöste molekulare Ionen mit einer Femtosekundenspektroskopie auf der Basis von Einzelreaktionsereignissen untersucht. Für die zur simultanen Speicherung von atomaren und molekularen Ionen notwendige Radiofrequenzfalle wurde eine transportable Vakuumapparatur konzipiert und realisiert sowie die zugehörigen Lasersysteme aufgebaut und eingerichtet. Um die Ultrahochvakuumbedinungen bei 2e-10 mbar auch bei häufiger Molekülpräparation gewährleisten zu können, wurde ein modularer Aufbau gewählt, bei dem Präparations- und Expermentierbereich durch differentielle Pumpstrecken voneinander getrennt sind. Durch diese hindurch führt ein 48 cm langer Quadrupolionenleiter, in welchem Ionen zwischen den Kammern transferiert werden können. Entlang des Ionenleiters ermöglichen ringförmige Gleichspannungselektroden eine dreidimensionale Speicherung der Ionen. Im Rahmen dieser Arbeit wurde mit atomaren 24Mg+ und molekularen 24MgH+ Ionen gearbeitet. Erstere werden durch Photoionisation von Magnesiumatomen aus einem thermischen Strahl erzeugt und ihre Bewegungsenergie durch Laserkühlung soweit reduziert, dass sie in etwa 20 μm Abstand voneinander in einer kristallinen Struktur erstarren. Magnesiumhydridionen werden nach Einleiten von Wasserstoffgas in einer photochemischen Reaktion mit 24Mg+ generiert und – von verbleibenden atomaren Ionen sympathetisch gekühlt – auf Gitterplätze des Kristalls integriert. Bei der Laserkühlung von 24Mg+ ausgesendete Fluoreszenzphotonen ermöglichen die optische Detektion der Ionen mit derzeit bis zu 1 μm Ortsauflösung. Die nicht fluoreszierenden molekularen Ionen werden indirekt als vermeintlich unbesetzte Stellen der Kristallstruktur sichtbar. Neben der Demonstration des Erfolges unseres Fallenkonzepts sowie dessen Charakterisierung bildet der verlustfreie, kontrollierte Transport von atomaren und molekularen Ionen aus dem Präparations- in den Experimentierbereich, eine wichtige Errungenschaft, welche zu einem kontinuierlichen Nachladen von Ionen mit einer Rate von über 100 Hz ausgebaut werden kann. Diese Arbeit präsentiert eine Machbarkeitsstudie zur Kombination von Präzisionsmethoden zweier Forschungsgebiete. Dazu wurde die Fallenapparatur mit einem weiteren Vakuumsystem, in dem ultraviolette Femtosekundenpulse erzeugt werden können, über ein System von differenziellen Pumpstrecken verbunden. Als Resultat werden 5 fs zeitaufgelöste Pump-Probe Experimente vorgestellt, die die Oszillation eines Vibrationswellenpaketes von individuellen 24MgH+ Molekülionen zeigen. Dabei wird die Bewegung des Wellenpaketes auf die Dissoziationswahrscheinlichkeit in einem bestimmten Zerfallskanal abgebildet. Einzelne Reaktionsereignisse konnten eindeutig nachgewiesen und daraus das zeitabhängige Verhalten extrahiert werden. Diese Resultate untermauern das Potenzial der von uns angestrebten Kombination der exzellenten Kontrolle über externe und interne Freiheitsgrade gespeicherter Ionen mit der extremen Zeitauflösung von modernen Kurzpulslasern. Weitere Arbeiten können die Vorteile beider Gebiete nutzen um bisher unzugängliche Experimente zu realisieren. Die besonderen Eigenschaften der präsentierten Apparatur sollten es beispielsweise erlauben, einzelne isolierte molekulare Ionen mit hoher räumlicher Präzision und wohl kontrollierten Anfangsbedingungen für zukünftige Strukturuntersuchungen mittels derzeit entstehender, intensiver Kurzpuls-Röntgenquellen an freien Elektronenlasern bereitzustellen.

In the concordance LCDM cosmological model, galaxies form in the centers of dark matter halos and merge with one another following the mergers of their host halos. Thus, we set out to quantify the growth mechanisms of dark matter halos. For this purpose, we analyze several large N-body simulations of the growth of cosmic structure. We devise a novel merger tree construction algorithm that properly takes into account halo fragmentations. We find that the merger rate evolves rapidly with redshift but depends weakly on mass, and that the proportions between mergers of different mass ratios, e.g. major and minor mergers, are universal. We also show that the merger rate per progenitor halo (related to future mergers and to galaxy pair counting) is smaller than that per descendant halo (related to past mergers and galaxy disturbed morphplogies), and that their redshift and mass dependencies are different. We find that only ~60% of the mass accreted onto halos arrives in mergers that are resolved in our simulations. Moreover, the functional form of the merger rate suggests that the merger contribution saturates at that value. Using full particle histories, we confirm that smoothly-accreted particles make a significant fraction of dark matter halos. This has important implications for the smoothness of gas accretion.

Disk galaxies at z~2 are rapidly star-forming, but show regular rotation, indicating little merger activity. We use a large dark matter simulation to show that even non-merging z~2 halos grow fast enough to explain observed high star-formation rates. We also follow those halos to z=0, finding that many do not undergo major mergers at all. The z~2 disks also show high velocity dispersions and irregular clumpy morphologies. We run "zoom-in" cosmological hydrodynamical simulations focusing on the formation of individual z~2 galaxies. We find that the clumpy morphologies are a result of gravitational instability, where the high random motions make the (turbulent) Jeans scales as large as the observed giant clumps. Star-formation feedback in our model is implemented as galactic winds with high mass-loading factors. We find that the high mass-loading factors prevent the clumps from virializing. Within roughly half a disk orbital time, they lose a large fraction of their mass, such that they stop collapsing and disrupt. Thus, their lifetimes are short and they do not migrate to the galaxy centers as has been proposed in the literature so far. We compare simulated galaxies to observations using radiative transfer calculations, and by creating mock SINFONI/VLT data cubes with realistic "observing conditions". We find good agreement between "observed" simulated galaxies and real observed ones, in terms of their luminosities, colors, morphologies and kinematics. With this comparison, we conclude that the galaxies formed in our simulations are plausibly realistic.

Magnetic fields in the Universe are found in almost all studied environments. In particular, their presence in the inter-galactic medium and in the intra-cluster medium

is confirmed by diffuse radio emission as well as by observations of Faraday Rotation Measures towards polarized radio sources within or behind the magnetized medium.

Besides the observations, their dynamical importance in astrophysical systems is poorly constrained, therefore there are still plenty of processes in which the role of magnetic fields are not fully understood.

Astrophysical systems are complex and highly nonlinear. Therefore, numerical simulations have demonstrated to be a useful tool to study those problems. However, the inclusion of magnetic fields in numerical implementations is not easy to achieve. Mainly because of the difficulties to keep the ∇ · B constraint low, and to have a stable implementation in different circumstances.

We study and developed a cosmological MHD code in SPH. We study different possible schemes to regularize the magnetic field, and avoid instabilities. Those schemes included

the use of Euler potentials to build the magnetic field, as well as cleaning schemes for the numerical ∇ · B errors.

We studied the magnetic field evolution in the context of cosmological structure formation of galaxy clusters. We compare different numerical schemes leading us to

the conclusion that the ∇ · B terms do not drive the evolution and growth of the magnetic field in galaxy clusters. We made synthetic rotation measure maps and study

the reversals of the magnetic field in comparison with observations. The comparison between observations and high resolution simulations, suggests that the physics may be

described by a multi scale turbulence model. This means that the turbulent dynamo driven by the cosmological cluster formation process works effectively, reproducing basic

properties from observations, even to details shown in structure functions and converging to the observation when we increase the resolution. We clearly demonstrates that using advanced schemes together with very high resolution allow to probe the properties of the ICM.

Additionally, we investigate the magnetic fields and their relation with the cosmic structure in which they are embedded. In general, the observed rotation measure signal

is strongly dominated by denser regions (e.g. those populated by galaxy clusters and groups), and in unclear how is their transition to low density regions, because there is

difficult to acquire direct magnetic field information of those regions.

Therefore statistical tools, such as correlation functions have to be used. To do so, we use cosmological simulations and try to mimic all the possible observation biases to

constrain actual measurements. We find that the shape of the cross-correlation function using a normalized estimator (in absence of any noise or foreground signal) nicely reflects

the underlying distribution of magnetic field within the large scale structure.

However, current measurement errors suppress the signal in such a way that it is impossible to relate the amplitude of the cross-correlation function to the underlying

magnetization of the large scale structure

In this work I present the characterization of the spatial distribution of X-ray galaxy clusters, based on the the measurements of the cluster power spectrum. The analysis is

developed on the new ROSAT-ESO Flux-Limited X-Ray (REFLEX II) galaxy cluster catalogue. This new sample extends the flux limit of the original REFLEX to 1.8×10−12

erg s−1 cm−2, yielding a total of 911 clusters with 94% completeness in redshift followup. The X-ray luminosity function was measured and parameterized in order to be

used as cosmological probe. The statistical analysis is complemented by creating a set of 100 REFLEX II-like mock catalogues, built from a suite of large volume LCDM Nbody

simulations (L-BASICC II). We have characterized the main properties of this set of simulations, such as the halo abundance, the halo bias, the halo clustering and the

mass-X-ray luminosity relations, all these required to properly understand the observed clustering signal of X-ray galaxy clusters. The mock catalogues have been designed to reproduce the observed X-ray luminosity function by calibrating the a mass-X ray luminosity relation. Our measurements of the X-ray cluster power spectrum are in

agreement with predictions from the LCDM cosmological model and show the expected increase in the amplitude of the power spectrum with increasing X-ray luminosity.

The better statistics of the REFLEX II sample allowed us to explore the issue of luminosity bias in some detail. On large scales it was observed a scale-independent

relative luminosity bias, which implies that the clustering of galaxy clusters, on those scales, is a scaled version of the clustering of dark matter. Moreover, this suggests

that within the precision given by the surveyed volume of the REFLEX II catalogue, the shape of the measured galaxy cluster power spectrum is not affected by distortions

induced due to the presence of clusters with different X-ray luminosities. We confirmed this result by implementing a luminosity dependent power spectrum estimator. The measured power spectrum is statistically compatible with a featureless power spectrum

on scales k > 0.01 h/Mpc and hence no statistically significant signal of baryonic acoustic

oscillations has been detected. Similar conclusions are drawn from the analysis of the clustering in configurations space by means of the cluster correlation function. For the

first time, a signature of non-linear evolution in the galaxy cluster power spectrum has

been detected on scales k~0.15 h/Mpc. We model the shape of the measured power spectrum by means of phenomenological parameterizations, which are useful for our

measurements due the moderate volume probed by the survey. The measurements of cluster power spectrum described in this work are suitable to be used as probes for

cosmological parameters.

In the current cosmological scenario clusters, that are the biggest virialized systems of the

Universe, are formed through accretion of smaller objects from the cosmic web in which they are

embedded. During these events the galaxies involved are modified due to interaction with other

galaxies, the cluster hot X-ray emitting gas and the cluster potential well. Some of mechanisms

acting in dense environments are tidal stripping, mergers and ram pressure stripping, just to name a

few. These mechanisms involved in galaxy evolution are also responsible for the formation of what

is called the intracluster light (ICL). ICL consists of stars in clusters that are not bound to any cluster

member. Numerical simulations predict that the stars contributing to the ICL component are unbound

by the processes that are involved in galaxy evolution and in the formation of the brightest cluster cD

galaxies in particular.

The aim of this work is to study the ICL component in the central core of Hydra I. Hydra I is a

medium compact cluster in the Southern Hemisphere at a distance of 50 Mpc. The cluster, a relaxed

system from X-ray observations, is dominated by two non interacting elliptical galaxies, NGC 3311

(cD) and NGC 3309 (E3). We are interested in the kinematic relation between the ICL component

and the cD halo of NGC 3311 and in exploring what can be understood from the photometric and

kinematic characteristics of the ICL about the evolutionary history of the cluster as a whole.

We studied the core of Hydra I using three different kinds of data. With UT1-FORS2 longslit

spectroscopy we investigated the absorption line kinematics of NGC 3311. With UT1-FORS2

multislit-imaging spectroscopy we probed the kinematics of the Planetary Nebulas (PNs) tracing

the stellar light in the central 100 × 100 kpc2 of the cluster, around NGC 3311. Finally, with

WFI-ESO2.2m telescope photometry we studied the light distribution around the cD galaxy and its

substructures.

The absorption line kinematics of NGC 3311 shows that the stellar halo of NGC 3311 is

dominated by the central intracluster stars of the cluster. The transition from predominantly galaxybound

stars to cluster stars occurs in the radial range from 4 to 12 kpc from the center of the galaxy.

The diffuse light in the Hydra I cluster is still un-mixed. The PN line-of-sight velocity distribution

(LOSVD) shows a multi-peaked structure and reveals the presence of subcomponents in the cluster

core. From V-band photometric data we discovered an excess of light, with respect to a symmetric

distribution, in the North-East part of the halo of NGC 3311. The excess has a velocity compatible

with the velocity of the PNs contributing to a high-velocity peak in the PN LOSVD and a group of

dwarf galaxies populating the central core of the Hydra I cluster. The excess of light could have

formed from stars unbound from the small group of dwarf galaxies that were partially disrupted

during a recent close passage through the dense cluster core and which are now behind NGC 3311.

The stellar population and structural properties of one of the DWs, HCC 26, are consistent with those

of other dwarf elliptical galaxies.

We conclude that even if from X-rays Hydra I appears to be the prototype of a relaxed and

dynamically evolved cluster, the build up of the diffuse light and halo of its central cD galaxy,

NGC 3311, is still ongoing.