WSRT Virgo HI filament survey

To learn more about the large-scale structures and accretion processes, the extended environment of galaxies have to be observed. Numerical simulations predict a cosmic web of extended structures and gaseous filaments.

To observe the direct vicinity of galaxies, column densities have to be achieved that probe the regime of Lyman limit systems. Typically, HI observations are limited to a brightness sensitivity of N_HI_~10^19^cm^-2^, but this has to be improved by ~2 orders of magnitude. With the Westerbork Synthesis Radio Telescope (WSRT), we mapped the galaxy filament connecting the Virgo Cluster with the Local Group.