The COSMOS HST ACS Observations Webpage

Anton Koekemoer, STScI

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HST/ACS Cycle 12 and Cycle 13 Data


This page describes the COSMOS data obtained with HST ACS/WFC, which is a detector comprised of two CCDs, each 2048x4096 pixels, with a scale of approximately 0.05"/pixel. The Cycle 12 data consisted of a total of 270 orbits of which 261 were obtained in I-band (F814W) and 9 orbits in g-band (F475W). Each orbit consists of 4 exposures, each 500 seconds in length, dithered in a 4-point box pattern to move the gap between the CCDs and obtain uniform coverage of each field, as well as provide sub-pixel dithering.

Image processing

The V1.2 images for the full 270 orbits from Cycle 12 have been produced by combining them with the MultiDrizzle software (Koekemoer et al. 2002) using the latest improved geometric distortion corrections for the ACS camera, together with improved absolute astrometry for each pointing. The images have been registered onto the fundamental astrometric frame for COSMOS, which makes use of the CFHT Megacam i-band image. The CFHT image (courtesy of Olivier LeFevre, Herve Aussel, Henry McCracken, et al.) is tied to the USNO-B1.0 system, which in turn has been tied to the VLA 1.4 GHz image (courtesy Eva Schinnerer and Chris Carilli). These V1.2 ACS images therefore supercede the V1.0 and V1.1 images, and should provide an absolute accuracy of order 0.05-0.1" or better. All images have the same pixel scale = 1 ACS pixel = 0.05"/pixel with North up, and are 5600x5600 pixels (thus 120 Mb each).

Please use these mosaics for your science. If you do so, please reference my paper describing full details of all the HST/ACS observations and reductions:

Koekemoer, A. M. et al. 2007, ApJS 172, 196

Image availablity

Alll images have been publicly released and delivered to IRSA and MAST, where they can also be retrieved from: