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Discovery of a giant gas tail in the galaxy group HCG 44

Submitter: Paolo Serra
Description: Galaxy groups are very busy places. Within a group galaxies interact with one another via tidal forces and, as a result, dramatic changes in their shape can take place. Furthermore, these interactions can strip galaxies of part of the gas they contain and so remove material which could have been used to form new stars. Indeed, astronomers believe that star-forming spiral galaxies can be turned into inactive lenticulars inside groups. Galaxy groups may therefore be the key to understand why the balance between the number of spirals and the number of lenticulars changes during the life of the Universe.

A team lead by ASTRON's Paolo Serra has recently discovered a group of galaxies which shows just how spectacular galaxy evolution within groups can be. Today's image shows the group HCG 44 with a combination of CFHT/MegaCam and GALEX images. The bluest galaxy in the group and its closest neighbour are NGC 3187 and NGC 3190. They both show clear signs of tidal interaction. The real surprise however came only after a very sensitive observation of the group with the Westerbork telescope obtained as part of the ATLAS3D project. This revealed the presence of a giant tail of neutral hydrogen gas (shown in orange in the image) which is 300 kiloparsec long and is as massive as 500 million solar masses.

In an article submitted for publication on MNRAS Serra and collaborators suggest that the tail may be made of gas stripped from NGC 3187 by the tidal field of the group. They estimate that the galaxy may have lost 1/3 of its original gas mass in less than a billion years. This discovery demonstrates how elusive evidence of gas stripping in groups is and that very sensitive observations over a large field are crucial if we want to gather a complete census of this kind of events in the nearby Universe.
Copyright: ASTRON and ATLAS3D team
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