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The Spindle Unwound

Submitter: Tom Oosterloo
Description: NGC 2685 is a galaxy with many names, e.g., The Helix galaxy, The Pancake or The Spindle Galaxy. The reason it has many names is that it is a very unusual galaxy. From the optical picture (left) it is clear that it is not a galaxy that falls in the standard categories of spiral or elliptical. Several suggestions have been made about the nature of this galaxy, but a recent detailed study, based on WSRT observations of the neutral hydrogen in NGC 2685, now seems to have given the final answer.

It was long thought that the galaxy harbours two kinematical systems, an inner disk and a separate outer disk that are at right angles to each other (see inset). Such an arrangement would explain the twisted velocity field of the galaxy (see colourful inset). The deep WSRT data (blue image on the right), however, show that although indeed the inner and outer gas disk are perpendicular to each other, they are connected by a faint, gas bridge. This means that NGC 2685 has a single, albeit very warped, disk and not two separate entities. This may seem a subtle difference, but it completely changes the ideas about how NGC 2685 must have formed. As a result, it may turn out that NGC 2685 may tell us something about the properties of dark matter.

More details can be found in a paper that soon will appear in Astronomy & Astrophysics: Jozsa, Oosterloo, Morganti, Klein and Erben: Kinematic modeling of disk galaxies III. The warped "Spindle" NGC 2685 http://arxiv.org/abs/0810.3025
Copyright: Astron
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