Galactic structure, near and far

We investigate galactic structure in closeby galaxies inside the local group as well as in distant galaxies. In the first chapter, we present a homogeneously selected sample of high resolution R-band images of the central regions of 67 early-type galaxies obtained with the Wide Field and Planetary Camera 2 (WFPC2) aboard the Hubble Space Telescope (HST). We find complex morphologies of the central regions of early-type galaxies which have become apparent from previous studies with HST, in particular various forms of dust, embedded stellar disks, and disk-like structures misaligned with the main galaxy. We analyze the luminosity profiles of the galaxies in our sample, and classify galaxies according to their central cusp slope. To a large extent we confirm the results from previous HST surveys in that early-type galaxies reveal a clear dichotomy: the bright ellipticals (M _B $\lesssim$ −20.5) are generally boxy and have luminosity profiles that break from steep outer power-laws to shallow inner cusps (referred to as “core” galaxies). The fainter ellipticals, on the other hand, typically have disky isophotes and luminosity profiles that lack a clear break and have a steep central cusp (referred to as “power-law” galaxies).; In the second part of this dissertation we go from the central cores of the galaxies to its outer parts, the halos. The flat rotation curves of late-type galaxies indicate that galaxies possess besides the visible matter an unknown yet gravitationally dominating component called “dark matter” (DM), located in halos which reaches far beyond the visible matter. In recent years, microlensing surveys towards the LMC have found an event rate which can be interpreted as being caused by a lens population of astrophysical dark matter located in the Galactic halo (e.g., Alcock et al., 2000b). Other possible, alternative explanations for the observed microlensing event rate include lensing by a previously undetected thick disk component of the Milky way, self-lensing of the LMC, or an intervening dwarf galaxy or tidal tails. The different candidate populations can be broadly categorized into any lensing caused by a uniform foreground lensing population (screen-lensing ), and lensing for which the lensing population is spatially close to the source population (self-lensing). The goal of the SuperMacho project, a next generation microlensing survey towards the LMC, is to determine which or what mixture of these two categories causes the observed microlensing rates by utilizing their spatial differences in lensing rates. We introduce the difference image analysis pipeline which is essential to handle the enormous amount of data, and perform completeness tests by adding fake stars. (Abstract shortened by UMI.)...