Properties of Quasistellar Objects and their progenitors in the radio and mm wavelength regimes in the context of ULIRG-to-QSO evolution

Abstract

The thesis at hand presents the results of a study of galaxies with active galactic nuclei (AGN) carried out in the radio and mm wavelength regimes at low and high angular resolutions. The studied objects cover a broad range of mechanisms responsible for powering the engines of the respective galaxies: ULIRGs (UltraLuminous Infrared Galaxies), a product of mergers between galaxies that are supposedly powered by starbursts, AGN or a mixture of the two, and QSOs (quasi-stellar objects) which are powered by AGN. Since ULIRGs and QSOs show similar properties (especially the infrared luminosities), it was proposed that they form the early and late phase of an evolutionary sequence where supposedly ULIRGs are the dust enshrouded progenitors of QSOs. As a prototypical ULIRG, Arp 220 represents an early-to-intermediate phase object in the scheme of the ULIRG-to-QSO evolution. For this object observations at multiple mm wavelengths and angular resolutions with the IRAM Plateau de Bure Interferometer (PdBI) are presented and analyzed. Arp 220 as a whole is studied in CO emission of the more extended structure. Furthermore, Arp 220-East is analyzed in more detail in the CO gas. Indications for emission ~10 towards the south, as well as to the north and to the west of the two nuclei, were found in the low resolution CO(1-0) maps. The work on this source was complemented by performing an N-body simulation of the merger of the two precursor galaxies of Arp 220. From the modeling the mass ratio of the disks of the progenitor galaxies was determined to be 1:2. The best t of the model parameters to the available data resulted in an age for the merger of 6x10^8 years. The 27 studied sources from the sample of nearby low-luminosity QSOs however, are representatives of the nal stage in the afore mentioned evolutionary scheme. In this part of the thesis, the properties of these nearby QSO host galaxies are studied in the mm and cm wavelength regimes: Several of the sources have been probed for HI. 45% of the sample sources were detected in HI with gas masses between 1.1x10^9 and 3.8x10^10 M_sun. The comparison to the atomic gas content of our Galaxy showed a factor of ~2 higher than the median gas mass for the sample sources. Indications for interactions in some QSO hosts were found in the HI spectra as well as in the DSS (Digitized Sky Survey) images. Their morphological appearance of the QSOs is a topic also addressed in this thesis, as well as the far-infrared (FIR) properties of the sample objects. A study of the water vapor megamaser transition at 22 GHz continues this work. No detection was found. Additionally, the knowledge about water megamasers is reviewed and the dierences between the two classes of active galactic nuclei, Seyfert galaxies and QSOs, are discussed in terms of the unied scheme for water megamaser emission. In the course of the almost 3 years of work leading to this thesis, I performed the reduction of all data shown (except the data reduction of the PdBI CO data for Arp 220) myself, and conducted and set up the biggest part of all observations for the sample of nearby low-luminosity QSO host galaxies. All analyses and simulations presented in this work were performed by me.