While dark matter is used to explain the galaxy rotation problem I am not aware of any dark matter models that show how dark matter is supposed to behave outside of galaxies? I have read one paper where it was proposed that the amount of visible matter within galaxies and outside galaxies were equivalent but I have not seen any papers that specifically relate to dark matter inside and outside of galaxies. Does anybody have any info or is this just something that is 'understood'? http://www.space.com/34926-dark-matter-not-so-clumpy.html
You might find this interesting : - from : https://www.forbes.com/sites/starts...axies-have-the-most-dark-matter/#47209b317671 - by Ethan Siegel : "Whether we're looking at the fluctuations in the cosmic microwave background, the lensing-to-X-ray ratios of colliding clusters, the way large-scale structure clumps together or the rotation properties of the largest spiral and elliptical galaxies, that same ratio -- of dark matter outmassing normal matter by a 5-to-1 ratio -- exists everywhere. Everywhere, that is, until you start looking at the tiniest galaxies in the Universe. All the way down to Milky Way-sized galaxies, which represents the vast majority of galaxies we've discovered in the Universe, that 5-to-1 ratio remains constant. But when you go to smaller galaxies, down to dwarf galaxies in clusters or ultra-low-mass galaxies visible only in our local group (due to their tiny light output), you find that the less mass there is overall, the greater the dark matter fraction is." - the ^above quoted^ from, and more at Link : https://www.forbes.com/sites/starts...axies-have-the-most-dark-matter/#47209b317671 These may also help to sate your curiosity : - from The Astrophysical Journal, Volume 746, Number 1 - "Matter Distribution Around Galaxies" by Shogo Masaki, Masataka Fukugita, and Naoki Yoshida - at Link : http://iopscience.iop.org/article/1...C7154BC4726BA8D1815.c1.iopscience.cld.iop.org - and this : "Large–Scale Structure Formation: from the first non-linear objects to massive galaxy clusters" by S. Planelles, D.R.G. Schleicher, and A.M. Bykov - at Link : https://arxiv.org/pdf/1404.3956.pdf maybe...
Would you believe this example ? First-ever image of dark matter? http://earthsky.org/space/waterloo-image-dark-matter-cosmic-web-2017
They're playing pretty loose with the definition of image. Buried pretty deep in the article: It is still inferred from gravitation of the masses that are seen, in that they don't interact how they are supposed to solely our theories of gravity. Or something like that ...
From that article, repeated verbatim from source at http://www.ras.org.uk/news-and-pres...e-of-a-dark-matter-web-that-connects-galaxies At a guess the first highlighted should read something like "They combined more than 23,000 separate lensing images of a galaxy pair", if it's to sensibly match with the second one.
Given the incorrect comment here: http://www.sciforums.com/threads/dark-matter-visualized.159235/#post-3449895 I will further elaborate on #5 above. Another possible interpretation of passage quoted there is that the 'two galaxies' with that gravitational lensing determined DM density contour are not real but a simulated 'typical example'. Either way, the article wording never makes it clear just what is being shown in the image. An enhancement - owing to many overlaid snapshots - of a particular actual galaxy pair with DM between. Or a synthetic representation of what gravitational lensing between many such pairs typically looks like. Probably the latter - given there were no astronomical coordinates or catalogue designation of 'the galaxy pair'.
