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Based on a consensus recommendation of a Scientific Advisory Committee to the STScI Director Steven Beckwith, supported by planning documents from a local Working Group, the parameters below have been adopted for the HST/ACS Ultra Deep Field.

Pointing

The UDF will consist of a single ultra-deep field (412 orbits in total) within the CDF-S GOODS area. The pointing will be RA(J2000)=3 32 39.0 and Decl.(J2000)=-27 47 29.1 These coordinates have been changed slightly in May 2003 due to guide star availability and implementation issues. We have attempted to include in the field both a spectroscopically confirmed z=5.8 galaxy and a spectroscopically confirmed type Ia SN at z=1.3. The pointing avoids the gaps with the lowest effective exposure on the Chandra ACIS image of CDFS.

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A complementary Treasury Program, with Rodger Thompson as PI, has also imaged the UDF with NICMOS as a 3x3 mosaic. This field is shown as red within the primary UDF field. In turn these NICMOS data have parallels and particularly noteworthy are the large fields covered by the ACS parallels, to the right and below, which are themselves among the deepest ACS public images available. Please read further for a more detailed description of the fields overlay diagram.

Filters/Expected Depth

The survey will use four filters: F435W (56 orbits), F606W (56 orbits), F775W (150 orbits), and F850LP (150 orbits). Based on the ACS planning document, the limiting AB magnitudes below are expected for extended source which gives S/N of 10 in aperture =0.2 sq arcsec (For WFC this is 9x9 pix). Average zodiac and Earthshine are assumed. The F435W (B) and F606W (V) exposures will be ~1 magnitude deeper than the equivalent HDF filters. The F775W (I) exposure will be ~1.5 magnitude deeper than the equivalent HDF exposure. The depth in F775W and F850LP is optimized for searching very red objects at the detection limit of the F850LP image.

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ACS Phase II and Status

The phase II is accessible on the web as DD proposal 9978

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