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The HIPASS Bright Galaxy Survey
The HI Parkes All-Sky Survey (HIPASS) has provided the rst ever survey of extragalactic neutral
hydrogen (H i) over the sky. This survey was completed in March 2000 and the data released in May
2000 (see www.atnf.csiro.au/multibeam/release). An extension into the northern hemisphere to the
northern limit of the Parkes telescope is ongoing. Extensive eorts are now underway to mine the rich
HIPASS data set. The most important eort is in nding and cataloguing the galaxies, both previously
known galaxies and newly discovered galaxies. Considerable eort is being contributed by the teams
at the University of Melbourne, the Swinburne Centre for Astrophysics and Supercomputing, and the
ATNF. One of the rst products is the HIPASS Bright Galaxy Catalogue, which is a catalogue of the
1000 apparently brightest H i galaxies in the southern hemisphere.
The HIPASS Bright Galaxy Catalogue represents the rst unobscured view of the nearby galaxy dis-
tribution in the southern sky. Neutral hydrogen gas in galaxies can be detected easily where optical
and infrared surveys are limited by the dust and stars of our own Galaxy. Therefore HIPASS easily
lls in large areas of previously `blank' sky, revealing the overall extent of galaxy large-scale structure.
In Figure 1 we show the spatial distribution of the brightest HIPASS galaxies. Of these, 84 have
no counterparts cataloged in the NASA/IPAC Extragalactic Database. Most of the newly discovered
galaxies lie in or close to the optical `Zone-of-Avoidance' (see Figure 2), with 58 at Galactic latitudes
less than 10 degrees, 38 galaxies at less than 5 degrees (see also Henning et al. 2000, AJ, 119, 2686).
There are 21 new galaxies at latitudes greater than 15 degrees. For 17 galaxies, the HIPASS and
optical velocities disagree. ATCA and optical follow-ups of these and many other galaxies are under
way to conrm their identication.
The new galaxies found outside the Zone-of-Avoidance can be divided into two groups, those with
optical counterparts and those without, the latter being very rare. Figure 3 shows several examples
of the rst kind: mostly compact, late-type galaxies, some close to nearby stars. We detected HI
1225+01 (the Virgo cloud; Haynes & Giovanelli 1989) and a new tidal cloud, HIPASS J0731-69, well-
separated from its apparent host galaxy NGC 2442 (see the article by Stuart Ryder et al.). Also
remarkable was the detection of HIPASS J1712{64 (Kilborn et al. 2000, AJ 120, 1342) and later
HIPASS J1718{59 (Koribalski et al. 2001, in prep.) plus several others without any obvious optical
counterparts. Their striking location along the Supergalactic Plane leads to speculation that they may
be the dregs of the galaxy formation process. However, it is also quite possible that they represent a
new kind of high-velocity ejecta from the Magellanic system as has been predicted in some simulations.
Figure 4 shows the velocity distribution of the 1000 brightest HIPASS galaxies (orange) compared to
the 1000 brightest optical galaxies (selected from the Lyon/Meudon Extragalactic Database using blue
magnitude). As the overall H i distribution is dominated by galaxies with systemic velocities between
800 and 2000 km s 1 the most outstanding structures in Figure 1 are the Supergalactic Plane and
the Local Void. Several new galaxies with velocities above 1000 km s 1 have been found which better
dene the boundaries of the Local Void. Although we know from optical surveys that the galaxy large-
scale structure is far from homogeneous, it is important to study the sky uninhibited by obscuration.
Many known structures continue into and across the optical Zone-of-Avoidance and create a beautiful
network of galaxies, dominated by groups, strings and bubbles.
Barbel Koribalski (ATNF), Lister Staveley-Smith (ATNF), Virginia Kilborn (Melbourne University),
Stuart Ryder (AAO) and the HIPASS/ZOA teams.

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Figure 1: Aito projection of the 1000 brightest HIPASS galaxies. | The symbols and colors de-
note dierent velocity ranges: v sys < 1000 (blue stars), 1000 { 2000 (green triangles), 2000 { 3000 (red
circles), and > 3000 km s 1 (grey squares).
Figure 2: Latitude histogram of the 1000 brightest HIPASS galaxies; new galaxies are marked in red.
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Figure 3: Displayed are optical images (from the the Digitized Sky Survey) of ten new galaxies detected
in the HIPASS Bright Galaxies Survey (latitudes jbj > 15 degrees).
Figure 4: Histogram of the H i systemic velocities of the 1000 brightest HIPASS galaxies (orange). The
velocity range from {1300 to +8000 km s 1 was searched, except for the span from {350 to +350 km s 1
where only known galaxies with an H i peak ux >120 mJybeam 1 were added. For comparison we
added the velocity histogram of the 1000 brightest optical galaxies (black).
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