The
HI Parkes All Sky Survey (
HIPASS) was an astronomical survey for
neutral atomic hydrogen (HI)The hydrogen line, 21 centimeter line or HI line refers to the electromagnetic radiation spectral line that is created by a change in the energy state of neutral hydrogen atoms. This electromagnetic radiation is at the precise frequency of 1420.40575177 MHz, which is equivalent to the vacuum...
. Data was taken between 1997 and 2002 using the
Parkes ObservatoryThe Parkes Observatory is a radio telescope observatory, 20 kilometres north of the town of Parkes, New South Wales, Australia. It was one of several radio antennas used to receive live, televised images of the Apollo 11 moon landing on 20 July 1969....
. HIPASS covered 71% of the sky and identified 5317 sources emitting HI's signature wavelength. Discoveries include the Leading Arm of the
Magellanic StreamThe Magellanic Stream is a high-velocity cloud of gas connecting the Large and the Small Magellanic Clouds. It came into existence by a near-collision of both galaxies some 2.5 billion years ago.-Discovery and early observations:...
and gas clouds devoid of
starA 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.
Survey
HIPASS observations had a
redshiftIn physics , redshift happens when light seen coming from an object is proportionally increased in wavelength, or shifted to the red end of the spectrum...
range of -1,280 to 12,700 km s-1. HIPASS was the first blind HI survey to cover the entire
southern skyIn astronomy and navigation, the celestial sphere is an imaginary sphere of arbitrarily large radius, concentric with the Earth and rotating upon the same axis. All objects in the sky can be thought of as projected upon the celestial sphere. Projected upward from Earth's equator and poles are the...
.
Southern Sky observations
Observations of the southern sky started in February 1997, and were completed in March 2000, consisting of 23020 eight-degree scans of each of 9 minutes duration. HICAT, the catalogue of HIPASS, contains 4315 HI sources. HIPASS scanned the entire southern sky five times.
Northern Sky observations
Northern HIPASS extended the survey into the
northern skyIn astronomy and navigation, the celestial sphere is an imaginary sphere of arbitrarily large radius, concentric with the Earth and rotating upon the same axis. All objects in the sky can be thought of as projected upon the celestial sphere. Projected upward from Earth's equator and poles are the...
. The entire
Virgo ClusterThe Virgo Cluster is a cluster of galaxies whose center is 53.8 ± 0.3 Mly away in the constellation Virgo. Comprising approximately 1300 member galaxies, the cluster forms the heart of the larger Local Supercluster, of which the Local Group is an outlying member...
region was observed in Northern HIPASS. NHICAT, the catalogue of the northern extension of HIPASS contains 1002 HI sources.
Multibeam Receiver
Observations for HIPASS were taken using the Parkes 21 cm Multibeam Receiver. The instrument consists of a
Focal Plane ArrayFocal Plane Arrays are arrays of receivers placed at the focus of a radio-telescope. Traditional radio-telescopes have only one receiver at the focus of the telescope, but radio-telescopes are now starting to be equipped with focal plane arrays, which are of three different types: multi-beam feed...
of 13 individual receivers arranged in a hexagonal pattern. Built in a collaboration between numerous institutions, it was funded by the
Australian Research CouncilThe Australian Research Council is the Australian Government’s main agency for allocating research funding to academics and researchers in Australian universities. Its mission is to advance Australia’s capacity to undertake research that brings economic, social and cultural benefit to the...
(ARC) and the
Australia Telescope National FacilityThe 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....
(ATNF) to undertake the HIPASS and ZOA surveys.
Leading arm of Magellanic Stream
HIPASS discovered the Leading Arm of the Magellanic Stream. This is an extension of the Magellanic Stream beyond the
Magellanic cloudsThe two Magellanic Clouds are irregular dwarf galaxies visible in the southern hemisphere, which are members of our Local Group and are orbiting our Milky Way galaxy...
. The existence of the Leading Arm is predicted by models of a
tidal interactionA galactic tide is a tidal force experienced by objects subject to the gravitational field of a galaxy such as the Milky Way. Particular areas of interest concerning galactic tides include galactic collisions, the disruption of dwarf or satellite galaxies, and the Milky Way's tidal effect on the...
between the Magellanic Clouds and the Milky Way.
HIPASS J0731-69
HIPASS J0731-69 is a cloud of gas devoid of any stars. It is associated with the asymmetric spiral galaxy
NGC 2442NGC 2442 / 2443 is an intermediate spiral galaxy about 50 million light-years away in the constellation Volans. It was discovered by Sir John Herschel. Associated with this galaxy is HIPASS J0731-69, a cloud of gas devoid of any stars...
. It is likely that HIPASS J0731-69 was torn loose from NGC 2442 by a companion.
HIPASS J1712-64
HIPASS J1712-64 is an isolated extragalactic cloud of neutral hydrogen with no associated stars. The cloud is a binary system and is not dense enough to form stars. HIPASS J1712-64 was probably ejected during an interaction between the Magellanic clouds and the Milky way.
New galaxies in the Centaurus A/M83 Group
Ten new galaxies were identified in the Centaurus A/M83 Group, bringing the total (at the time) to 31 galaxies.