Extragalactic molecular clouds and chemistry of diffuse interstellar clouds

Zusammenfassung Since the discovery of a cold molecular component of the interstellar medium in the 1970s, it has been realized that most of the dark clouds are actually molecular clouds, consisting mainly of molecular hydrogen and some amount of dust and other molecules. Nowadays, molecular clouds are recognized as places of star-formation in the Milky Way and other galaxies. Therefore, studies of the structure, physical conditions, and chemical compositions of these objects are of paramount importance, since they allow us to understand the process of star formation. This thesis presents the study of giant molecular clouds in the giant elliptical radio galaxy NGC5128 (Centaurus A) and an analysis of the chemical composition of diffuse interstellar clouds. Using dust as tracer of molecular hydrogen, and detecting the clouds by a multi-scale wavelet based method we derive basic parameters of the molecular clouds in NGC5128. We show that the slope of the mass spectrum of molecular clouds is significantly steeper than that of Galactic clouds. Our near-infrared study of the nucleus region of the giant elliptical galaxy NGC1316 (Fornax A) reveals a ”peanut-shape” structure in the nucleus, which was hidden behind dense dust lanes. We estimate the sizes of the structure and, applying optical and nearinfrared kinematical data, propose several possible explanations of the complex nuclear morphology. The chemical analysis of diffuse interstellar clouds leads us to a discovery of a new class of objects – Ca-Fe interstellar clouds. They turn out to be rare (just a few examples among ∼ 300 lines of sight) objects with the Ca i 4227 Åas well as Fe i 3720 Åand 3860 Ålines stronger than those of K i (near 7699 Å) and Na i (near 3302 Å), occupying volumes different from the well-known interstellar H i clouds where the K i and ultraviolet Na i lines are dominant features. We establish that the CaFe clouds can be found only along sightlines toward hot, luminous (and thus distant) objects with high rates of mass loss. We also suggest a new consistent system of the oscillator strength of several unsaturated methylidyne bands. Based on optical spectra of a sample of stars we estimate methylidyne column densities. Finally, we study spatial correlations of some diffuse interstellar bands (DIB) and simple molecules. We find that radial velocities of CH, CH features, and two narrow DIBs at 6196 and 4964 Åsuggest that the 6196 DIB carrier is spatially correlated with CH, while the 4964 DIB carrier prefers environments where the CH molecule is abundant. Using a statistically meaningful sample of reddened OB stars and analyzing correlations between CH and CH column densities and DIB strengths we clearly confirm this suggestion.