<IMG SRC="/images/sci/nor/ngc891.jpg">
<H2>ISO detects signal from dark matter in a galaxy similar to the Milky Way</H2>

A true colour photograph of the edge-on Spiral galaxy NGC 891 (field of view is 6.7 x 6.7 arcminutes). The dark band running through the center of the disk is caused by the effect of large dust clouds in this galaxy. At 8 positions in this disk, even beyond the field of this photo, the ISO-SWS has detected the signal from molecular hydrogen gas (H2). 

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The graphical inset shows the signal of the H2 lines at 17.0 and 28.2 micrometer wavelength, detected at the outermost position of the survey, at a distance 12 kilo parsec (37000 light-years) from the center, a position where other observations of lines of molecules, like the CO molecule, are trailing into the noise. From the ratio of the signal strength of these lines a temperature of the gas of about 80K is derived.

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Credits:<BR>
ISO-SWS data from Valentijn and van der Werf / SRON <BR>
Optical photograph of NGC 891: Blair Savage, Chris Howk (U. Wisconsin)/N.A.Sharp
(NOAO)/AURA/NSF <BR>

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These observations were discussed in details in a ESA Science Web Note:

<P> &nbsp; &nbsp; &nbsp; "<A HREF="http://sci.esa.int/science-e/www/object/index.cfm?fobjectid=12820">[<EM>ISO detects signal from dark matter in a galaxy similar to the Milky Way</EM>]</A>"<BR>

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<B>High-resolution images of the Galaxy NGC891 are available at NOAO:</B>

<A HREF="http://www.noao.edu/image_gallery/html/im0002.html">http://www.noao.edu/image_gallery/html/im0002.html</A>
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