Hubble Deep Field South
Encyclopedia
Hubble Space Telescope
The Hubble Space Telescope is a space telescope that was carried into orbit by a Space Shuttle in 1990 and remains in operation. A 2.4 meter aperture telescope in low Earth orbit, Hubble's four main instruments observe in the near ultraviolet, visible, and near infrared...
's Wide Field and Planetary Camera 2
Wide Field and Planetary Camera 2
The Wide Field and Planetary Camera 2 is a baby grand piano sized camera built by the Jet Propulsion Laboratory and formerly installed on the Hubble Space Telescope. It was installed by servicing mission 1 in 1993, replacing the telescope's original Wide Field and Planetary Camera...
over 10 days in September and October 1998. It followed the great success of the original Hubble Deep Field
Hubble Deep Field
The Hubble Deep Field is an image of a small region in the constellation Ursa Major, constructed from a series of observations by the Hubble Space Telescope. It covers an area 2.5 arcminutes across, two parts in a million of the whole sky, which is equivalent in angular size to a 65 mm tennis...
in facilitating the study of extremely distant galaxies
Galaxy
A galaxy is a massive, gravitationally bound system that consists of stars and stellar remnants, an interstellar medium of gas and dust, and an important but poorly understood component tentatively dubbed dark matter. The word galaxy is derived from the Greek galaxias , literally "milky", a...
in early stages of their evolution
Galaxy formation and evolution
The study of galaxy formation and evolution is concerned with the processes that formed a heterogeneous universe from a homogeneous beginning, the formation of the first galaxies, the way galaxies change over time, and the processes that have generated the variety of structures observed in nearby...
. While the WFPC2 took very deep optical images, nearby fields were simultaneously imaged by the Space Telescope Imaging Spectrograph
Space Telescope Imaging Spectrograph
The Space Telescope Imaging Spectrograph is a spectrograph, also with a camera mode, installed on the Hubble Space Telescope. It operated continuously from 1997 until a power supply failure in 2004. After repairs, it began operating again in 2009...
(STIS) and the Near Infrared Camera and Multi-Object Spectrometer
Near Infrared Camera and Multi-Object Spectrometer
The Near Infrared Camera and Multi-Object Spectrometer is a scientific instrument for infrared astronomy, installed on the Hubble Space Telescope , operating from 1997 to 1999, and from 2002 to 2008...
(NICMOS).
Planning
The rationale behind making another Deep Field image was to provide observatories in the southern hemisphereSouthern Hemisphere
The Southern Hemisphere is the part of Earth that lies south of the equator. The word hemisphere literally means 'half ball' or "half sphere"...
with a similarly deep optical image of the distant universe as had been provided to those in the northern hemisphere
Northern Hemisphere
The Northern Hemisphere is the half of a planet that is north of its equator—the word hemisphere literally means “half sphere”. It is also that half of the celestial sphere north of the celestial equator...
.
The field chosen was in the constellation
Constellation
In modern astronomy, a constellation is an internationally defined area of the celestial sphere. These areas are grouped around asterisms, patterns formed by prominent stars within apparent proximity to one another on Earth's night sky....
of Tucana
Tucana
Tucana is a constellation in the southern sky, created in the late sixteenth century. Its name is Latin for the toucan, a South American bird.-History:...
at a right ascension
Right ascension
Right ascension is the astronomical term for one of the two coordinates of a point on the celestial sphere when using the equatorial coordinate system. The other coordinate is the declination.-Explanation:...
of and declination
Declination
In astronomy, declination is one of the two coordinates of the equatorial coordinate system, the other being either right ascension or hour angle. Declination in astronomy is comparable to geographic latitude, but projected onto the celestial sphere. Declination is measured in degrees north and...
of . As with the original Hubble Deep Field
Hubble Deep Field
The Hubble Deep Field is an image of a small region in the constellation Ursa Major, constructed from a series of observations by the Hubble Space Telescope. It covers an area 2.5 arcminutes across, two parts in a million of the whole sky, which is equivalent in angular size to a 65 mm tennis...
(referred to hereafter as the 'HDF-N'), the target area was selected to be far from the plane of the Milky Way
Milky Way
The Milky Way is the galaxy that contains the Solar System. This name derives from its appearance as a dim un-resolved "milky" glowing band arching across the night sky...
's galactic disk, which contains a large amount of obscuring matter, and to contain as few galactic star
Star
A star is a massive, luminous sphere of plasma held together by gravity. At the end of its lifetime, a star can also contain a proportion of degenerate matter. The nearest star to Earth is the Sun, which is the source of most of the energy on Earth...
s as possible. However the field is closer to the galactic plane than the HDF-N, meaning that it contains more galactic stars. It also has a nearby bright star, as well as a moderately strong radio source close by, but in both cases it was decided that these wouldn't compromise follow-up observations.
As with the HDF-N, the field lies in Hubble's Continuous Viewing Zone (CVZ), this time in the south, allowing twice the normal observing time per orbit. At specific times of year, the HST can observe this zone continuously, without it being eclipsed by the Earth
Earth
Earth is the third planet from the Sun, and the densest and fifth-largest of the eight planets in the Solar System. It is also the largest of the Solar System's four terrestrial planets...
. Viewing this field, however, has some issues due to passages through the South Atlantic Anomaly
South Atlantic Anomaly
The South Atlantic Anomaly is an area where the Earth's inner Van Allen radiation belt comes closest to the Earth's surface. This leads to an increased flux of energetic particles in this region and exposes orbiting satellites to higher than usual levels of radiation...
and also with scattered earthshine during daylight hours; the latter can be avoided by using instruments with larger sources of noise, for example from the CCD reading process, at those times. The survey again used Director's Discretionary Time.
The field was imaged briefly on October 30–31, 1997 to make sure that the guide stars in the field were acceptable; these guide stars would be required to keep the HST accurately pointing on the region during the observations proper.
Observations
The observing strategy for the HDF-S was similar to that of the HDF-N, with the same optical filters used for the WFPC2 images (isolating wavelengths at 300, 450, 606 and 814 nanometres), and similar total exposure times. The observations were made over 10 days in September and October 1998, a total of 150 orbits. While the WFPC2 took very deep optical images, the fields were simultaneously imaged by the Space Telescope Imaging SpectrographSpace Telescope Imaging Spectrograph
The Space Telescope Imaging Spectrograph is a spectrograph, also with a camera mode, installed on the Hubble Space Telescope. It operated continuously from 1997 until a power supply failure in 2004. After repairs, it began operating again in 2009...
(STIS) and the Near Infrared Camera and Multi-Object Spectrometer
Near Infrared Camera and Multi-Object Spectrometer
The Near Infrared Camera and Multi-Object Spectrometer is a scientific instrument for infrared astronomy, installed on the Hubble Space Telescope , operating from 1997 to 1999, and from 2002 to 2008...
(NICMOS). A number of flanking fields were also observed for shorter periods of time.
The WFPC2 image is 5.3 square arcminutes, whilst the NICMOS and STIS images are only 0.7 square arcminutes.
| Camera | Filter | Wavelength | Total exposure time | Exposures |
|---|---|---|---|---|
| WFPC2 | F300W | 300 nm (U-band) | 140,400 s | 106 |
| WFPC2 | F450W | 450 nm (B-band) | 103,500 s | 67 |
| WFPC2 | F606W | 606 nm (V-band) | 99,300 s | 53 |
| WFPC2 | F814W | 814 nm (I-band) | 113,900 s | 57 |
| NICMOS NIC3 | F110W | 110 nm (J-band) | 162,600 s | 142 |
| NICMOS NIC3 | F160W | 160 nm (H-band) | 171,200 s | 150 |
| NICMOS NIC3 | F222M | 222 mm (K-band) | 105,000 s | 102 |
| STIS | 50CCD | 350–950 nm | 155,600 s | 67 |
| STIS | F28X50LP | 550–960 nm | 49,800 s | 64 |
| STIS | MIRFUV | 150–170 nm | 52,100 s | 25 |
| STIS | MIRNUV | 160–320 nm | 22,600 s | 12 |
| Spectroscopy | G430M | 302.2–356.6 nm | 57,100 s | 61 |
| Spectroscopy | G140L | 115–173 nm | 18,500 s | 8 |
| Spectroscopy | E230M | 227.8–312 nm | 151,100 s | 69 |
| Spectroscopy | G230L | 157–318 nm | 18,400 s | 12 |
As with the HDF-N, the images were processed using a technique known as 'drizzling', in which the telescope pointing was changed by a very small amount between exposures, and the resulting images combined using sophisticated techniques to achieve a higher angular resolution
Angular resolution
Angular resolution, or spatial resolution, describes the ability of any image-forming device such as an optical or radio telescope, a microscope, a camera, or an eye, to distinguish small details of an object...
than would otherwise be possible. Translational changes were fine during the imaging parts of the observation; however, the telescope had to be rotated by small amounts instead of repointed during the spectroscopic work, such that the centre of the STIS instrument was kept on the central quasar. The HDF-S final image had a pixel
Pixel
In digital imaging, a pixel, or pel, is a single point in a raster image, or the smallest addressable screen element in a display device; it is the smallest unit of picture that can be represented or controlled....
scale of 0.0398 arcseconds.
Contents of the HDF-S
The cosmological principleCosmological Principle
In modern physical cosmology, the cosmological principle is the working assumption that observers on Earth do not occupy an unusual or privileged location within the universe as a whole, judged as observers of the physical phenomena produced by uniform and universal laws of physics...
states that at the largest scales, the universe is homogenous and isotropic, meaning that it should look the same in any direction. The HDF-S would thus be expected to strongly resemble the HDF-N, and this was indeed the case, with large numbers of galaxies visible displaying a similar range of colours and morphologies to those seen in the HDF-N, and very similar numbers of galaxies in each of the fields.
One difference with the HDF-N was that the HDF-S included a known quasar
Quasar
A quasi-stellar radio source is a very energetic and distant active galactic nucleus. Quasars are extremely luminous and were first identified as being high redshift sources of electromagnetic energy, including radio waves and visible light, that were point-like, similar to stars, rather than...
with a redshift
Redshift
In physics , redshift happens when light seen coming from an object is proportionally increased in wavelength, or shifted to the red end of the spectrum...
value of 2.24, J2233-606, discovered during the search for the target field. The quasar provides a probe of the gas along the line of sight where the foreground objects are also observed, allowing an investigation into the association of galaxies with absorption features. Including a quasar in the field of view was originally considered for the HDF-N, but was decided against due to concerns about increased numbers of galaxies associated with the quasar might skew the galaxy number counts, and because there was not a favourably located quasar. For the Southern field, however, such a skewed count wasn't a concern due to the known counts from the HDF-N.
Scientific results
As with the HDF-N, the HDF-S provided rich pickings for cosmologistsPhysical cosmology
Physical cosmology, as a branch of astronomy, is the study of the largest-scale structures and dynamics of the universe and is concerned with fundamental questions about its formation and evolution. For most of human history, it was a branch of metaphysics and religion...
. Many studies of the HDF-S confirmed results found from the HDF-N, such as star formation
Star formation
Star formation is the process by which dense parts of molecular clouds collapse into a ball of plasma to form a star. As a branch of astronomy star formation includes the study of the interstellar medium and giant molecular clouds as precursors to the star formation process and the study of young...
rates over the lifetime of the universe. The HDF-S was also extensively used in studies of how galaxies evolve over time, both due to internal processes and encounters with other galaxies.
Followup observations
Following Hubble's observations of the HDF-S field, the field was also surveyed in the UV/optical/infrared frequency range by the Anglo-Australian ObservatoryAnglo-Australian Observatory
The Australian Astronomical Observatory , formerly the Anglo-Australian Observatory, is an optical/near-infrared astronomy observatory with its headquarters in suburban Sydney, Australia...
, the Cerro Tololo Interamerican Observatory and the European Southern Observatory
European Southern Observatory
The European Southern Observatory is an intergovernmental research organisation for astronomy, supported by fifteen countries...
. At mid-infrared it was observed by the Infrared Space Observatory
Infrared Space Observatory
The Infrared Space Observatory was a space telescope for infrared light designed and operated by the European Space Agency , in cooperation with ISAS and NASA...
, and radio observations were made by the Australia Telescope National Facility
Australia Telescope National Facility
The Commonwealth Scientific and Industrial Research Organisation 's radio astronomy observatories are collectively known as the Australia Telescope National Facility , with the facility supporting Australia's research in radio astronomy....
.