ACS Observations of Galaxies in 'Protoclusters'
Roderik Overzier
I will present results from our on-going HST/ACS imaging survey of
galaxy overdensities associated with distant, luminous radio galaxies out to
z=5. The targeted radio galaxies are all surrounded by an overdensity of Lya
galaxies discovered from groundbased narrow-band imaging. Multi-filter ACS
images are used to find additional galaxies associated with these
'protoclusters' using the Lyman break technique, resulting in the discovery of
a clear excess of LBGs towards a target at z=4.1. Our medium deep,
high-resolution ACS observations may contribute to the current understanding of
cluster formation and evolution.