Quote:
Originally Posted by Shiraz
Hi Robert - thanks for the info. FWIW, attached a "sort of" isophote representation from the current image that might be of interest - it sure is a big galaxy.
Ray
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Thanks very much for that, Ray,
The details in your image confirm some of the subtle internal structures I have been noting in other images of NGC 6876
This is my second most favourite elliptical galaxy (after PGC 48896) on account of the fact that it has very significant internal structure that is easily evident.
For instance, the outermost isophotes of NGC 6876, in your image, and in many other images of this galaxy, are a long way from being regular ellipses.
In the literature, we do find some speculations that the noticeably unusual overall morphology of this galaxy could be due to a merger between galaxies. However,
the extremely-extended outer envelope of NGC 6876 has had very very little study, so far, in the professional literature.
Oddly enough, "6876" might be
the least known bright elliptical galaxy in the sky, despite its obvious strong abnormalities! (This undoubtedly has to do with its far southern declination, which puts it outside of the "mental map" of the majority of professional astronomers)
Normally, with the isophotes of the vast majority of elliptical galaxies, the deviations in isophotal shape from a perfect ellipse are very subtle;
so the strong deviations from regularity in the outer parts of this galaxy represent a very significant abnormality.
It is remarkable how little the outermost regions of elliptical galaxies are understood by professional astronomers;
for example, even the 'familiar' M86 ,which looks to be a relatively normal elliptical in its inner parts, has a
highly peculiar outer envelope which is neither that of an S0 galaxy or that of an elliptical with a significant excess outer light.
(in other words, M86 cannot be assigned to a single unique Hubble type!!).
The outer parts of elliptical galaxies show large variations in their morphologies. So it is perhaps not unexpected that spectroscopic and kinematic studies have shown that the stellar orbits within elliptical galaxies and also the orbits of their globular clusters , also vary a lot between various elliptical galaxies.
For example, this recent study shows that the distributions, the rotation, the orbits, and the ages, of the systems of globular clusters that trace the outermost regions of elliptical galaxies, vary a lot from galaxy to galaxy:
http://researchbank.swinburne.edu.au...ular&y=21&x=11
So there is a lot of diversity in the population of elliptical galaxies, it is just not so obvious as in those "pretty" spirals!
Cheers, Robert