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.