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The
HI Parkes All Sky Survey (HIPASS) survey was conducted with
20cm multi-beam receiver on the Parkes 64m telescope, Murriyang,
in the late 1990s and early 2000s.
HIPASS J1131–31 was discovered in that survey as a source
of HI emission at low redshift, but in such close proximity to a bright
star that optical follow-up observations were not possible at the time.
However, the star turned out to be a fast-moving one, and with time
it has moved far enough away from the line-of-sight to the galaxy
that the galaxy can now be studied.
Hubble Space Telescope images resolve
the dwarf irregular galaxy into stars, leading to a distance estimate of
7 Mpc (23 million light years). Spectral optical observations with the Southern African
Large Telescope reveal HIPASS J1131–31 to be one of the most extremely
metal-poor galaxies known.
Karachentsev et al. have dubbed it the Peekaboo galaxy because of the way it has been
hiding and because of its potential importance.
The red giant branch of the system is tenuous compared with the prominence of
the features of young populations in the color-magnitude diagram,
inviting speculation that star formation in the galaxy only began in
the last few Gyr.
The image above is an optical HST image of the dwarf galaxy HIPASS J1131–31, with
dimensions of 70 arcseconds × 45 arcseconds. The 10.4 magnitude foreground star
is located ∼15 arcsec to the North. The spikes of the HST's diffraction pattern,
caused by light diffracting around the struts supporting the secondary mirror,
are evident in the image.
The results will be published in the
Monthly Notices of the Royal Astronomical Society.
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