Atomic neutral hydrogen gas in and around
galaxies is detected via the 21-cm spectral line of hydrogen. The Magellanic System is a great
example where neutral hydrogen (HI) is found in both the Large Magellanic Cloud (LMC) and
the Small
Magellanic Cloud (SMC), a bridge between the two neighbouring galaxies
as well as an extended stream - the Magellanic Stream - tracing their
gravitational interactions with the Milky Way. The few bright dots in the
middle of the image are hydrogen emission from more distant galaxies in the
Sculptor Group. The data for this study (published in Nature by Mary
Putman et al.)
are from the HI Parkes All Sky
Survey (HIPASS), which was carried out over several years with the
21-cm multibeam receiver on the 64-m Parkes Telescope. The
13 horns of the innovative multibeam receiver
system allowed for a survey speed 13 times faster than previously possible.
In the near future, phased array
feeds will provide even larger field of views and consequently faster
survey speeds.
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