Cophasing LINC-NIRVANA and molecular gas in low-luminosity QSO host and cluster galaxies

Bertram, Thomas (2007). Cophasing LINC-NIRVANA and molecular gas in low-luminosity QSO host and cluster galaxies. PhD thesis, Universität zu Köln. Open Access

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Abstract

This thesis consists of two parts. The first part reports on the development of a fringe tracking system for LINC-NIRVANA, the near-infrared homothetic imaging camera for the Large Binocular Telescope (LBT). LINC-NIRVANA allows for a coherent combination of the light entering the two primary mirrors. The fringe pattern in the focal plane is required to be stable in time to preserve the high spatial frequency information in long exposure images. Atmospheric differential piston causes the position of the fringes to change with time. A fringe tracker is a servo system that measures and corrects for atmospheric differential piston in real-time. In the first part, numerical simulations of atmospheric turbulence are used to investigate the problem of angular anisoplanatism of differential piston. The fringe tracking concept and the top-level requirements are introduced, followed by a presentation of the mechanical design of the system. This design includes a solution for a device that is capable of positioning a detector with high precision within a cryogenic environment. A fitting algorithm determines the amount of differential piston in the point-spread function of a reference target. The performance of this algorithm under different signal-to-noise conditions is investigated. First polychromatic fringes obtained with a testbed interferometer conclude the first part. Measurements of millimeter CO transitions in extragalactic targets are the basis for the two observational studies in the second part of this thesis. The molecular gas content in low-luminosity QSO host galaxies is investigated and discussed together with far-infrared data. Unlike in most published studies, a far-infrared selection criterion was not applied. It is shown that the majority of low-luminosity QSO host galaxies is rich in molecular gas. These objects show different CO emission properties, depending on their central activity. The second study deals with a potential dependency of the molecular gas content in cluster galaxies on their distance to the center of the cluster. A deficiency of molecular gas in galaxies that are located in the vicinity of the center is indicated in a sample of Abell 262 galaxies. A model is presented that predicts a drop of gas and dust and explains it with the stripping of cirrus-like clouds.

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Thesis (PhD thesis)

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