@phdthesis{Streich2015,
  author    = {Streich, David},
  title     = {Understanding massive disk galaxy formation through resolved stellar populations},
  url       = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-81027},
  school      = {Universit{\"a}t Potsdam},
  pages     = {ix, 140},
  year      = {2015},
  abstract  = {In this thesis we utilize resolved stellar populations to improve our understanding of galaxy formation and evolution. In the first part we improve a method for metallicity determination of faint old stellar systems, in the second and third part we analyze the individual history of six nearby disk galaxies outside the Local Group. A New Calibration of the Color Metallicity Relation of Red Giants for HST data: It is well known, that the color distribution of stars on the the Red Giant Branch (RGB) can be used to determine metallicities of old stellar populations that have only shallow photometry. Based on the largest sample of globular clusters ever used for such studies, we quantify the relation between metallicity and color in the widely used HST ACS filters F606W and F814W. We use a sample of globular clusters from the ACS Globular Cluster Survey and measure their RGB color at given absolute magnitudes to derive the color-metallicity relation. We find a clear relation between metallicity and RGB color; we investigate the scatter and the uncertainties in this relation and show its limitations. A comparison with isochrones shows reasonably good agreement with BaSTI models, a small offset to Dartmouth models, and a larger offset to Padua models. Even for the best globular cluster data available, the metallicity of a simple stellar population can be determined from the RGB alone only with an accuracy of 0.3 dex for [M/H]<-1, and 0.15 dex for [M/H]>-1. For mixed populations, as they are observed in external galaxies, the uncertainties will be even larger due to uncertainties in extinction, age, etc. Therefore caution is necessary when interpreting photometric metallicities. The Structural History of Nearby Low Mass Disk Galaxies: We study the individual evolution histories of three nearby, low-mass, edge-on galaxies (IC5052, NGC4244, NGC5023). Using the color magnitude diagrams of resolved stellar populations, we construct star count density maps for populations of different ages and analyze the change of structural parameters with stellar age within each galaxy. The three galaxies show low vertical heating rates, which are much lower than the heating rate of the Milky Way. This indicates that heating agents, as giant molecular clouds and spiral structure are weak in low mass galaxies. We do not detect a separate thick disk in any of the three galaxies, even though our observations cover a larger range in equivalent surface brightness than any integrated light study. While scaleheights increase with age, each population can be well described by a single disk. Only two of the galaxies contain a very weak additional component, which we identify as the faint halo. The mass of these faint halos is less than 1\% of the mass of the disk. All populations in the three galaxies exhibit no or only little flaring. While this finding is consistent with previous integrated light studies, it poses strong constraints on galaxy formation models, because most theoretical simulations often find strong flaring due to interactions or radial migration. Furthermore, we find breaks in the radial profiles of all three galaxies. The radii of these breaks are independent of age, and the break strength is decreasing with age in two of the galaxies (NGC4244 and NGC5023). This is consistent with break formation models, that combine a star formation cutoff with radial migration. The differing behavior of IC5052 can be explained by a recent interaction or minor merger. The Structural History of Massive Disk Galaxies: We extend the structural analysis of stellar populations with distinct ages to three massive galaxies, NGC891, NGC4565 and NGC7814. While confusion effects due to the high stellar number densities in their central region, and the prominent dust lanes inhibit an detailed analysis of the radial profiles, we can study their vertical structure. These massive galaxies also have a slower heating than the Milky Way, comparable to the low mass galaxies. This can be traced back to their already thick young populations and thick layers of their interstellar medium. We do not find a clear separate thick disk in any of these three galaxies; all populations can be described by a single disk plus a S\'ersic bulge/halo component. In contrast to the low mass galaxies, we cannot rule out the presence of thick disks in the massive galaxies, because of the strong influence of the halo, that might hide the possible contribution of the thick disk to the vertical star count profiles. However, the faintness of the possible thick disks still points to problems in the earlier ubiquitous findings of thick disks in external galaxies.},
  language  = {en}
}
@phdthesis{Kamann2013,
  author    = {Kamann, Sebastian},
  title     = {Crowded field spectroscopy and the search for intermediate-mass black holes in globular clusters},
  url       = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus-67763},
  school      = {Universit{\"a}t Potsdam},
  year      = {2013},
  abstract  = {Globular clusters are dense and massive star clusters that are an integral part of any major galaxy. Careful studies of their stars, a single cluster may contain several millions of them, have revealed that the ages of many globular clusters are comparable to the age of the Universe. These remarkable ages make them valuable probes for the exploration of structure formation in the early universe or the assembly of our own galaxy, the Milky Way. A topic of current research relates to the question whether globular clusters harbour massive black holes in their centres. These black holes would bridge the gap from stellar mass black holes, that represent the final stage in the evolution of massive stars, to supermassive ones that reside in the centres of galaxies. For this reason, they are referred to as intermediate-mass black holes. The most reliable method to detect and to weigh a black hole is to study the motion of stars inside its sphere of influence. The measurement of Doppler shifts via spectroscopy allows one to carry out such dynamical studies. However, spectroscopic observations in dense stellar fields such as Galactic globular clusters are challenging. As a consequence of diffraction processes in the atmosphere and the finite resolution of a telescope, observed stars have a finite width characterized by the point spread function (PSF), hence they appear blended in crowded stellar fields. Classical spectroscopy does not preserve any spatial information, therefore it is impossible to separate the spectra of blended stars and to measure their velocities. Yet methods have been developed to perform imaging spectroscopy. One of those methods is integral field spectroscopy. In the course of this work, the first systematic study on the potential of integral field spectroscopy in the analysis of dense stellar fields is carried out. To this aim, a method is developed to reconstruct the PSF from the observed data and to use this information to extract the stellar spectra. Based on dedicated simulations, predictions are made on the number of stellar spectra that can be extracted from a given data set and the quality of those spectra. Furthermore, the influence of uncertainties in the recovered PSF on the extracted spectra are quantified. The results clearly show that compared to traditional approaches, this method makes a significantly larger number of stars accessible to a spectroscopic analysis. This systematic study goes hand in hand with the development of a software package to automatize the individual steps of the data analysis. It is applied to data of three Galactic globular clusters, M3, M13, and M92. The data have been observed with the PMAS integral field spectrograph at the Calar Alto observatory with the aim to constrain the presence of intermediate-mass black holes in the centres of the clusters. The application of the new analysis method yields samples of about 80 stars per cluster. These are by far the largest spectroscopic samples that have so far been obtained in the centre of any of the three clusters. In the course of the further analysis, Jeans models are calculated for each cluster that predict the velocity dispersion based on an assumed mass distribution inside the cluster. The comparison to the observed velocities of the stars shows that in none of the three clusters, a massive black hole is required to explain the observed kinematics. Instead, the observations rule out any black hole in M13 with a mass higher than 13000 solar masses at the 99.7\% level. For the other two clusters, this limit is at significantly lower masses, namely 2500 solar masses in M3 and 2000 solar masses in M92. In M92, it is possible to lower this limit even further by a combined analysis of the extracted stars and the unresolved stellar component. This component consists of the numerous stars in the cluster that appear unresolved in the integral field data. The final limit of 1300 solar masses is the lowest limit obtained so far for a massive globular cluster.},
  language  = {en}
}