Abstract

The galaxies strongly-lensed by foreground galaxy clusters provide outstanding laboratories to study the physical mechanisms that drive galaxy formation and evolution. Gravitational lensing by massive galaxy clusters is a powerful tool, allowing one: 1) to boost the brightnesses and sizes of the sources, and 2) to measure the distribution of total mass of dark plus visible matter in the lenses. Sources with certain favorable geometries of observer, lens, and source produce giant arcs and multiply-imaged galaxies. We will present spatially-resolved spectroscopy of some of these giant arcs and show how their star forming activities can be followed along the long axis of the galaxy and traced back onto their exact locations in the source plane. In one case, a galaxy source is sufficiently bright to enable high signal-to-noise absorption spectroscopy of the intervening intergalactic medium. The cluster galaxies, meanwhile, comprise old, red elliptical galaxies which are thought to have formed rapidly in an intense burst of star formation around the time of the peak epoch of star formation (z=2-4). We will present new data from Planck and Herschel on the search for the progenitors of massive galaxy clusters. The future will bring the discovery of the highest redshift galaxies using the combination of the James Webb Space Telescope and the right choice of ‘optics.’