Daily Image
07-04-2009
More HALOGAS survey - UGC 2082
| Submitter: | Gyula Jozsa |
| Description: | The central scientific aim of the WSRT HALOGAS survey (see daily image 6-Apr-09) is to investigate the origin of low-density neutral hydrogen in the outskirts of galaxies. The question to answer is how much of that diffuse gas is still related to the bright disk and how much might be attributed to a different component, the so-called gaseous halo, that may have a different origin and that may tell us something how galaxies form and grow (see also daily image 05-06-2007). The left image shows an overlay of the neutral gas distribution of the small spiral galaxy UGC 2082, a galaxy of the HALOGAS sample, on top of an optical (Digital Sky Survey) image. The bright part of the gas disk is coloured in magenta, the dimmer part in blue. The ellipses indicate the expected appearance of a flat disk. One can see that while the bright part is well confined to the inner ellipse (it is probably a flat disk), the outer part is not. There is an apparent excess of gas perpendicular to the disk. So, is this the gaseous halo? Not necessarily, since by analysing the spectroscopic data we found that the outer disk is warped. Taking the larger ellipse as reference, this is evident in the picture: the outer disk is not symmetric. The movie to the right shows our current model of the gas disk in UGC 2082, artificially made opaque. When the model has the orientation of UGC 2082, we show an image where the model disk is made translucent for comparison with the image to the left. Carefully distinguishing between warps and gaseous halos is one of the delicate tasks that lie ahead in analysing the exciting data sets from the HALOGAS survey. |
| Copyright: | Astron; We made use of the Digital Sky Survey |
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