Thursday, November 15, 2007

Ultra High Energy Cosmic Rays

Ultra High Energy Cosmic Rays: origin and propagation
We discuss the basic difficulties in understanding the origin of the highest energy particles in the Universe - the ultrahigh energy cosmic rays (UHECR). It is difficult to imagine the sources they are accelerated in. Because of the strong attenuation of UHECR on their propagation from the sources to us these sources should be at cosmologically short distance from us but are currently not identified. We also give information of the most recent experimental results including the ones reported at this conference and compare them to models of the UHECR origin.

The highest energy cosmic ray ever detected had the energy of a 290km/h tennis ball! From a single particle. Gasp.

Faint Irregular Galaxies

Gas rich galaxies from the FIGGS survey
The FIGGS (Faint Irregular Galaxy GMRT Survey) is aimed at creating a multi-wavelength observational data base for a volume limited sample of the faintest gas rich galaxies.

Some of these objects have very extreme dynamical mass to light ratios. Over 100 in some cases.
These very large dynamical mass to blue luminosity ratios naturally lead one to ask whether extremely gas rich dwarf galaxies have abnormally small baryon fractions, i.e. have they just been inefficient at forming stars, or did they end up with less than the typical baryon fraction?