COSMOS: Hubble Space Telescope Observations

The Cosmic Evolution Survey (COSMOS) was initiated with an extensive allocation (590 orbits in Cycles 12-13) using the Hubble Space Telescope ( HST ) for high-resolution imaging. Here we review the characteristics of the HST imaging with the Advanced Camera for Surveys (ACS) and parallel observations with NICMOS and WFPC2. A square field (1.8 deg 2 ) has been imaged with single-orbit ACS I -band F814W exposures with 50% completeness for sources 0.5” in diameter at I AB = 26.0 mag. The ACS is a key part of the COSMOS survey, providing very high sensitivity and high-resolution (0.09” FWHM and 0.05” pixels) imaging and detecting a million objects. These images yield resolved morphologies for several hundred thousand galaxies. The small HST PSF also provides greatly enhanced sensitivity for weak-lensing investigations of the dark matter distribution.