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Watching a galaxy forming

Submitter: Raffaella Morganti
Description: Deep images always bring surprises. Some time ago (see Daily Image 28-6-2006) we showed the discovery made with the WSRT of a huge disk of neutral hydrogen (more than 600,000 lightyear in diameter) around the radio galaxy B2 0648+27. This disk was interpreted as a signature that this galaxy has formed through the merging of two big gas-rich spiral galaxies and that it is now evolving toward a "relaxed and boring" elliptical galaxy.

The picture shows how this galaxy looks when observed in optical with a deep exposure (taken with the MDM - Kitt Peak telescope). Superimposed are the contours of the HI emission (detected with the WSRT).

The new deep optical image reveals that the galaxy is indeed not yet so "boring" and provides further evidence for the merger origin of B2 0648+27. The galaxy shows a distorted optical morphology, a broad tidal arm and a low surface-brightness stellar tail that curls around more than half the galaxy, following the large-scale HI ring-like structure. The gas and stars in this ring are most likely material tidally expelled during the merger and that now is slowly falling back onto the galaxy.

In B2 0648+27, we observe a time-delay between the merger event and the ignition of the radio source: the radio source starts quite late after the merger.

These results are presented in a paper by Emonts, Morganti, van Gorkom, Oosterloo, Brogt and Tadhunter published in Astronomy & Astrophysics http://xxx.lanl.gov/abs/0807.1541)
Copyright: ASTRON
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