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9th of August 2018
LVHIS images of M 83
The Local Volume HI Survey (LVHIS) was conducted with the Australia Telescope Compact Array (ATCA) in the 21cm band. The "Local Volume" of the Universe contains about 1000 galaxies within 30 million light years of the Milky Way. LVHIS studied galaxies previously detected with the Parkes 64-m telescope in the HI Parkes All Sky Survey (HIPASS). LVHIS mapped the distribution of neutral hydrogen with 20 times greater accuracy than LVHIS, and was also able to derive their rotation speeds, which are important for measuring the dark matter content of galaxies.

M 83 (HIPASS J1337-29) is a grand-design spiral galaxy with an unusually large HI (neutral hydrogen) envelope. It lies at a distance of about 5 Mpc (16 million light years) and forms the centre of a subgroup of ~10 known galaxies. The left-hand image above shows contours of the radio emission overlaid on an optical image of the galaxy, and the right-hand image shows the velocity distribution of material in the galaxy. The optical image shows M 83 together with its dwarf companions NGC 5264, IC 4316 and UGCA 36. The HI distribution of M 83, as mapped with LVHIS, is remarkable, and extends well beyond the optical extent of the galaxy, showing outer disc streamers, irregular enhancements, an asymmetric tidal arm, diffuse emission, and a thoroughly twisted velocity field. It is quite likely that M 83 has accreted dwarf galaxies in the past. More information about LVHIS is given in in this blog post by Baerbel Koribalski.

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