Format:
131 Seiten
,
Diagramme
Content:
Numerical simulations of galaxy formation and observational Galactic Astronomy are two fields of research that study the same objects from different perspectives. Simulations try to understand galaxies like our Milky Way from an evolutionary point of view while observers try to disentangle the current structure and the building blocks of our Galaxy. Due to great advances in computational power as well as in massive stellar surveys we are now able to compare resolved stellar populations in simulations and in observations. In this thesis we use a number of approaches to relate the results of the two fields to each other. The major observational data set we refer to for this work comes from the Radial Velocity Experiment (RAVE), a massive spectroscopic stellar survey that observed almost half a million stars in the Galaxy. In a first study we use three different models of the Galaxy to generate synthetic stellar surveys that can be directly compared to the RAVE data. To do this we evaluate the RAVE selection function to great detail. Among the Galaxy models is the widely used Besancon model that performs well when individual parameter distribution are considered, but fails when we study chemodynamic correlations. The other two models are based on distributions of mass particles instead of analytical distribution functions. This is the first time that such models are converted to the space of observables and are compared to a stellar survey. We show that these models can be competitive and in some aspects superior to analytic models, because of their self-consistent dynamic history. In the case of a full cosmological simulation of disk galaxy formation we can recover features in the synthetic survey that relate to the known issues of the model and hence proof that our technique is sensitive to the global structure of the model. We argue that the next generation of cosmological galaxy formation simulations will deliver valuable models for our Galaxy. Testing these models with our approach will provide a direct connection between stellar Galactic astronomy and physical cosmology. In the second part of the thesis we use a sample of high-velocity halo stars from the RAVE data to estimate the Galactic escape speed and the virial mass of the Milky Way. In the course of this study cosmological simulations of galaxy formation also play a crucial role. Here we use them to calibrate and extensively test our analysis technique. We find the local Galactic escape speed to be 533 (+54/-41) km/s (90% confidence). With this result in combination with a simple mass model of the Galaxy we then construct an estimate of the virial mass of the Galaxy. For the mass profile of the dark matter halo we use two extreme models, a pure Navarro, Frenk & White (NFW) profile and an adiabatically contracted NFW profile. When we use statistics on the concentration parameter of these profile taken from large dissipationless cosmological simulations we obtain an estimate of the virial mass that is almost independent of the choice of the halo profile. For the mass M_340 enclosed within R_340 = 180 kpc we find 1.3 (+0.4/-0.3) x 10^12 M_sun. This value is in very good agreement with a number of other mass estimates in the literature that are based on independent data sets and analysis techniques. In the last part of this thesis we investigate a new possible channel to generate a population of Hypervelocity stars (HVSs) that is observed in the stellar halo. Commonly, it is assumed that the velocities of these stars originate from an interaction with the super-massive black hole in the Galactic center. It was suggested recently that stars stripped-off a disrupted satellite galaxy could reach similar velocities and leave the Galaxy. Here we study in detail the kinematics of tidal debris stars to investigate the probability that the observed sample of HVSs could partly originate from such a galaxy collision. We use a suite of $N$-body simulations following the encounter of a satellite galaxy with its Milky Way-type host galaxy. We quantify the typical pattern in angular and phase space formed by the debris stars and develop a simple model that predicts the kinematics of stripped-off stars. We show that the distribution of orbital energies in the tidal debris has a typical form that can be described quite accurately by a simple function. The main parameters determining the maximum energy kick a tidal debris star can get is the initial mass of the satellite and only to a lower extent its orbit. Main contributors to an unbound stellar population created in this way are massive satellites (M_sat 〉 10^9 M_sun). The probability that the observed HVS population is significantly contaminated by tidal debris stars appears small in the light of our results
Note:
Dissertation Universität Potsdam 2013
Additional Edition:
Erscheint auch als Online-Ausgabe Piffl, Tilmann Models of the Galaxy and the massive spectroscopic stellar survey RAVE 2014
Language:
English
Keywords:
Stellarastronomie
;
Computersimulation
;
Spektroskopie
;
Radialgeschwindigkeit
;
Hochschulschrift
