Project Description
Overview
In December, 1995 the Hubble Space Telescope pointed at an
undistinguished high-galactic latitude patch of sky in the northern
hemisphere, and observed for 10 straight days. The result was the
deepest optical image of the sky yet obtained: The Hubble Deep
Field (HDF) (henceforth referred to as the Hubble Deep Field
North, or HDF-N). The images allow detection of sources as faint as V
= 30 in four bandpasses spanning the near-UV to the near-IR
(Williams et al. 1996). The data were released to the community
within one month of the observations and have been used in a wide
variety of projects and publications, ranging from studies of the
star-formation rate as a function of redshift, to studies of faint M
dwarfs in the Galactic halo.
A second Hubble Deep Field campaign was carried out between late
September and October of 1998. The raw, pipeline calibrated and
reprocessed data were released to the community on November 23,
1998. The rationale for undertaking a second deep field campaign
followed from the wealth of information that has come out of HDF-N,
and from the desire to provide a point of focus for similar studies of
the distant universe from southern-hemisphere facilities. The wide
public access to the HDF-N data stimulated extensive followup
observations across the electromagnetic spectrum, both from major
ground-based observatories and from other satellites. A similar level
of effort is anticipated for HDF-S. We are maintaining a `clearinghouse' for supporting and
follow-up observations of the HDF-S.
Test observations of the HDF-S field were
obtained in October, 1997. The primary purpose of the test was to
ensure that the guide stars to be used for the full campaign were
acceptable, but an initial reconnaissance of the field was also
carried out.
The HDF-S campaign differs from the HDF-N campaign in several
important areas:
- The field is located in the Southern Continuous Viewing
Zone. Choice of a field in the CVZ maximizes the observing efficiency
of HST. The J2000 coordinates of the HDF-S are given here).
- A moderate redshift quasar of z ~ 2.24, identified by Boyle,
Hewett, Weymann and colleagues, was placed in the STIS field for both
imaging and spectroscopy so that correlations between quasar
absorption redshifts and the redshifts of galaxies in the fields may
be determined. Information on the QSO can be found in papers by Sealey et
al. (1998) and by
Savaglio (1998).
- Simultaneous, parallel observations were made with the three HST
instruments STIS, WFPC2 and NICMOS of separate, neighboring fields.
The STIS and NICMOS observations are significant enhancements over
what was possible during the HDF-N campaign (although the HDF-N was
later observed with NICMOS by GTO and GO teams).
- The early planning of the HDF-S allowed several preparatory
studies to be carried out in advance, as collected on the HDF-S Clearinghouse web page.
The actual observations of the HDF-S were similar in spirit to the
original HDF. As was the case for HDF-N, approximately 150 consecutive
orbits were devoted to a single telescope pointing. Additional
flanking field observations were made surrounding the deep STIS, WFPC2
and NICMOS fields.
Layout Main Fields
The figure shows the position of the HDF-S overlayed on a deep ground-based image. The
image is a 3000s R-band exposure from the CTIO 4m telescope (courtesy
of Alistair Walker). North is up and East is left. The WFPC2 region is
to the West, the STIS region is to the East and NICMOS region is to
the South. The STIS field is centered on the quasar at z ~ 2.24.
Note that the figure is for illustrative purposes only. The overlaid
positions of the STIS and WFPC2 fields is accurate only to a few
arcsec. The overlaid positions of the NICMOS fields are accurate only
at the ~ 10 arcsec level. Use the calibrated J2000 coordinates of the
HDF-S) when higher accuracy overlays are required.
Click on the image to get a larger scale view of the field.
Layout Flanking Fields
As with the HDF-N, some time during the HDF-S campaign was devoted to
obtaining WFPC2 single-band images of a larger, contiguous area around
the primary imaging field (the "flanking fields"), to a typical depth
of I_AB ~ 25.5. The current plan is to observe a region about 7
arcmin in diameter, defined so as to include both the STIS and the
NICMOS primary target regions. The goals of the wide-area imaging are
to provide a large contiguous area for angular correlation studies,
especially interesting near the QSO; to yield better statistics for
less numerous, brighter galaxies; and to provide optical morphologies
for galaxies in the larger fields typical of ground-based multi-object
spectrographs.
The figure shows the tentative HDF-S flanking field arrangement as
laid out several months before the campaign, overlaid on an image
extracted from the Digitized Sky Survey. Note that the figure is for
illustrative purposes only. The arrangement used for the actual
campaign may have been slightly different, due to late changes in the
observing strategy. Consult the actual Observing logs or the header information
of the data files for more detailed information.
The red field is the main HDF-S WFPC2 field. The green fields are
flanking fields for the WFPC2 with the F814W filter. The blue fields
are the STIS CCD fields associated with the flanking fields, and the
yellow are flanking-fields for the NIC3 parallels with the F160W
filter. The main NIC3 field was observed for 9 orbits with the STIS
CCD (no filter). The right-most WFPC2 flanking field is the parallel
frame associated with that exposure.
Click on the image to get an overlay of the same flanking field
arrangement on the deeper
R-band ground-based CTIO image.
Observing strategy
Discussions about the observing strategy for the HDF-S focussed
primarily on the questions:
- What filters/gratings to use for each instrument ?
- What exposure time to use for each filter/grating ?
- How to choose the detailed instrumental setup and observing
parameters ?
- How to pack the observations into the individual orbits during
the campaign ? In CVZ observations, scattered earth light increases
the sky background in certain bandpasses on the day side of the
orbit. It was therefore essential to tailor the observations for all
the instruments to make optimal use of `bright' and `dark' time.
A detailed but outdated discussion of the observing strategy
for each of the individual instruments is available:
These discussions describe various general issues, as well as the
planned observing strategy as of July 1998. The strategy used for the
actual campaign was somewhat different, due to late changes in the
observing strategy. Consult the actual Observing logs or the header information
of the data files for more accurate and up-to-date information on the
observing strategy.
Send us your feedback or questions.
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page.
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This page was last updated on November 23, 1998.
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