Diffuse neutral hydrogen in the local universe

Promotie: dhr. A. Popping, 16.15 uur, Academiegebouw, Broerstraat 5, Groningen
Proefschrift: Diffuse neutral hydrogen in the local universe
Promotor(s): prof.dr. J.M. van der Hulst
Faculteit: Wiskunde en Natuurwetenschappen
Contact: Attila Popping, tel. 00 33 495 04 4100, e-mail: attila.popping@oamp.fr, popping@astro.rug.nl

Diffuse neutral hydrogen in the local universe

In the last years the realization has emerged, that galaxies do not dominate the mass budget of the Universe. Galaxies are the regions with the highest densities, in an underlying extended Cosmic Web. Imaging this structure is essential to better understand the evolution of galaxies and the Universe. Not only are galaxies formed here, this it is also the place where interaction happens between galaxies and the surrounding Intergalactic medium, which determines the life cycle of a galaxy. Numerical simulations predict that the Cosmic Web exists of extended and diffuse gas filaments, which are extremely hard to detect with current telescopes.

In this thesis we investigate diffuse gas regions in the Intergalactic medium, by using the 21-cm emission line of neutral hydrogen. In first instance we employ an advanced numerical simulation, from which the distribution of neutral hydrogen can be reconstructed. The statistical properties are compared with the statistics of earlier observations.

Observations from the Westerbork and Parkes radio telescopes are used to directly detect neutral hydrogen. The different data-sets cover the same region in the sky and are very sensitive to diffuse gas clumps. In the observations we find 16 new detections of neutral hydrogen at a very low brightness, that cannot be connected to a known galaxy. These new detections are potentially components of the Cosmic Web. With the observations we can increase our knowledge about the Intergalactic medium.