and Cosmology

9. The Universe at High Redshift
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Fig. 9.11. The Hubble Ultra-Deep Field,
afieldof∼ 3. ′ 4 × 3. ′ 4 observed by the ACS
camera. The limiting magnitude up to which
sources are detected in this image is about
one magnitude fainter than in the HDF.
More than 10 000 galaxies are visible in the
image, many of them at redshifts z ≥ 5
relatively red filters that are available provides us with
an opportunity to identify drop-out candidates at redshift
z ∼ 6; several such candidates have already been
verified spectroscopically.
One of the immediate results from the HDF was the
finding that the morphology of faint galaxies is quite
different from those in the nearby Universe. Locally,
most luminous galaxies fit into the morphological Hubble
sequence of galaxies. This ceases to be the case
for high-redshift galaxies. In fact, galaxies at z ∼ 2are
much more compact than local luminous galaxies, they
show irregular light distributions and do not resemble
any of the Hubble sequence morphologies. By redshifts
z ∼ 1, the Hubble sequence seems to have been partly
established.
Further Deep-Field Projects with HST: GOODS,
GEMS, COSMOS. The great scientific harvest from
the deep HST images, particularly in combination
with data from other telescopes and the readiness to
make such data available to the scientific community
for multifrequency analyses, provided the motivation
for additional HST surveys. The GOODS (Great Observatories
Origins Deep Surveys) project is a joint
observational campaign of several observatories, centering
on two fields of ∼ 16 ′ × 10 ′ size each that have
been observed by the ACS camera at several epochs between
2003 and 2005. One of these two regions contains
the HDF-N, the other a field that became known as the
Chandra Deep Field South (CDF-S). The Chandra satellite
observed both GOODS fields with a total exposure
time of ∼ 1 × 10 6 sand∼ 2 × 10 6 s, respectively. Also,
the Spitzer observatory took long exposures of these two
fields. In addition, several ground-based observatories
are involved in this survey, for instance by contributing
an ultra-deep wide field image (∼ 30 ′ × 30 ′ ) centered
on the CDF-S. The data themselves and the data products
(like object catalogs, color information, etc.) are
all publicly available and have already led to a large
number of scientific results. Even larger surveys using