Daily Image
16-10-2006
To the outer edge, and beyond...
| Submitter: | Tom Oosterloo |
| Description: | With better and more sensitive telescopes, one can see further and further away. But one can, of course, also have a better look at nearby objects. NGC 891 is a famous, nearby galaxy (only 30 million light-years away from us). It is a spiral galaxy seen perfectly edge on. For this reason, it is an ideal object to study the vertical structure of spiral galaxies. It has been observed with every telescope, usually more than once. The contours in the three pictures show (left to right, all on the same linear scale) the neutral hydrogen in NGC 891 as it was detected with the WSRT in 1979 (Sancisi & Allen), in 1997 (Swaters, Sancisi & van der Hulst) and in 2005 (Oosterloo, Fraternali & Sancisi). The images illustrate the progress of technology: the 1997 image is about a factor 10 deeper than the 1979 image, while the 2005 is again a factor 10 deeper than the 1997 image (and thus a factor 100 deeper than the 1979 image...). The deeper images reveal more and more neutral hydrogen, but interestingly the galaxy grows only in one direction. This indicates that the hydrogen detected in the outermost regions is gas that is shot out from the galaxy into space by exploding stars. However, the kinematics of the gas in the 2005 data also shows that in the very outer regions, this gas must be interacting with the inter-galactic medium, i.e. the stuff that floats in-between galaxies. The 2005 image is one of the deepest images ever taken of the neutral hydrogen in an external galaxy and will remain so for a while. We will have to wait for SKA for deeper images..... |
| Copyright: | Astron |
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