Editing Hubble Ultra-Deep Field (section)

==Planning==
In the years since the original [[Hubble Deep Field]], the [[Hubble Deep Field South]] and the [[GOODS]] sample were analyzed, providing increased statistics at the high [[redshift]]s probed by the HDF. When the [[Advanced Camera for Surveys]] (ACS) detector was installed on the HST, it was realized that an ultra-deep field could observe galaxy formation out to even higher redshifts than had currently been observed, as well as providing more information about galaxy formation at intermediate redshifts (z~2).<ref name="Beckwith2006" /> A workshop on how to best carry out surveys with the ACS was held at [[Space Telescope Science Institute|STScI]] in late 2002. At the workshop Massimo Stiavelli advocated an Ultra Deep Field as a way to study the objects responsible for the [[reionization]] of the Universe.<ref name="Stiavelli">{{cite journal |author1=M. Stiavelli |author2=S.M. Fall |author3=N. Panagia |title=Observable Properties of Cosmological Reionization Sources |journal=Astrophysical Journal |year=2004 |bibcode=2004ApJ...600..508S |doi=10.1086/380110 |arxiv=astro-ph/0309835 |volume=600 |issue=2 |pages=508–519|s2cid=1176087 }}</ref> Following the workshop, the STScI Director Steven Beckwith decided to devote 400 orbits of Director's Discretionary time to the UDF and appointed Stiavelli as the lead of the Home Team implementing the observations.

Unlike the Deep Fields, the HUDF does not lie in Hubble's Continuous Viewing Zone (CVZ). The earlier observations, using the [[Wide Field and Planetary Camera 2|Wide Field and Planetary Camera 2 (WFPC2)]] camera, were able to take advantage of the increased observing time on these zones by using wavelengths with higher noise to observe at times when [[earthshine]] contaminated the observations; however, ACS does not observe at these wavelengths, so the advantage was reduced.<ref name="Beckwith2006" />

As with the earlier fields, this one was required to contain very little emission from our galaxy, with little [[Zodiacal dust]]. The field was also required to be in a range of [[declinations]] such that it could be observed both by southern hemisphere instruments, such as the [[Atacama Large Millimeter Array]], and northern hemisphere ones, such as those located on [[Hawaii]]. It was ultimately decided to observe a section of the [[Chandra Deep Field South]], due to existing deep X-ray observations from [[Chandra X-ray Observatory]] and two interesting objects already observed in the GOODS sample at the same location: a redshift 5.8 galaxy and a supernova. The coordinates of the field are [[right ascension]] {{RA|3|32|39.0}}, [[declination]] {{DEC|-27|47|29.1}} ([[J2000]]). The field is 200 arcseconds to a side, with a total area of 11 square arcminutes,<ref name="Beckwith2006" /> and lies in the constellation of Fornax.<ref name="press_release" />