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22nd of January 2021
Choir groups from SINGG
by Dzudzar et al.
First there was HIPASS -- the HI Parkes All-Sky Survey -- which was carried out between 1997 and 2002 and detected over 5000 galaxies. A follow-up was SINGG -- the Survey of Ionization in Neutral Gas Galaxies -- which involved optical imaging of 468 HIPASS detections. Inspection of the SINGG images revealed 15 fields that had four or more emission line galaxies within the 15 arcminute HIPASS beam, and these SINGG groups were naturally named "Choirs"! Based on the total group neutral hydrogen content, it was found that Choir groups are in an early stage of a group assembly: they have an average star formation efficiency, and they are not significantly HI-deficient.

Dzudzar et al. have used the ATCA together with previously published data to study the HI content of 13 Choir groups. The image above shows the stellar mass versus distance, together with their histograms, for the Choir galaxies. The coloured stars show Choir galaxies detected in HI, while the open circles show Choir galaxies without detected HI. The circles within the grey diamonds are potentially HI-deficient galaxies. The green histograms show Choir galaxies with HI, the grey histograms show potentially HI-deficient galaxies and the white histograms show all Choir galaxies. The vertical dashed lines connect Choir galaxies within the same group, based on the adopted group distance, with their names are shown in the upper histogram. More details are give in the paper by Dzudzar et al., published in Monthly Notices of the Royal Astronomical Society.

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