Observational Cosmology
(T. Dahlén, C. Fransson, M. Näslund, M. Wold)

The emphasis of the group on observational cosmology has up to now mainly been on the study of clusters of galaxies at high and low redshifts, as well as their relation to active galactic nuclei (AGN). New directions also include modeling of early supernova activity, as well the use of supernovae as cosmological probes. In the latter field the group is collaborating with especially the cosmology group at the Dept. of Physics at Stockholm University.

In preparation for New Generation Space Telescope (NGST), we have used different assumptions for the combination of dust extinction and star formation up to redshifts $z \mathrel{\copy\simgreatbox}5$, as well as detailed modelling of supernova properties, to estimate the number of supernovae that should be observable with this telescope. Realistic light curves and spectral shapes that evolve with time for the different types supernovae are used. It is found that NGST should be able to detect several tens of core-collapse events in a single detection if the observational limit in the range $1-5~\mu$m is 1 nJy and the field is 16 square arcmin. The observable number of Type Ia supernovae is also estimated.