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Old 04-10-2011, 02:58 PM
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madbadgalaxyman (Robert)
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Join Date: Mar 2011
Location: Brisbane
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Very Good observation, Paddy, to disentangle the NGC 7174 plus NGC 7176 pair.

N7174 is a highly distorted object of "disky" morphology, with plenty of disturbed-looking dust, and it forms an overlap pair with the elliptical galaxy NGC 7176.

It looks like NGC 7174 is somehow stretched out, rather than being just a normal undisturbed galaxy:

Click image for larger version

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(The above image is from the Atlas of Structures in Early Type Galaxies.)

Of the four galaxies in this compact group of galaxies, which is known as Hickson Compact Group 90 (= HICK 90)(= HCG 90), it seems to me that NGC 7172 is the most likely to show some kind of internal structure in visual observations, as it has an "equatorial" dust lane which is quite broad and which is noticeably distorted and/or non-planar;

Click image for larger version

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The above image of NGC 7172 is a composite of two DSS images which I downloaded from the "Aladin previewer" (my favourite version of the Digitized Sky Survey).

I have in front of me a paper copy of Paul Hickson's "Atlas of Compact Groups of Galaxies", including images of all 100 compact groups; this Atlas is a nice tool for frontier-level visual observers, because the included images of the groups are not too detailed, so they do bear some relation to what can be seen visually.

cheers, Robert

P.S. NGC 7172 has a Seyfert nucleus, so you might be seeing some of the light from the Active Galactic Nucleus at the very centre of this galaxy..... but it is extremely hard to disentangle the contribution of the central active nucleus from that of the surrounding material (e.g. bulge light, central star formation, etc.)

Last edited by madbadgalaxyman; 04-10-2011 at 03:12 PM. Reason: more info
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