Hi Mike,
Thanks for pointing out your high-contrast version of your image.
As mentioned in my previous post, NGC 5084 has a
very unusual appearance. This galaxy is a really excellent subject for your ultra-deep imaging/exploration project, as the peculiar-looking outer disk is of extremely low surface brightness. In fact, if this galaxy were seen face-on, I have a feeling that the faint outer structures would be undetectable.
There exist a few individual galaxies, within the population of bright galaxies to apparent Blue magnitude 13.5, where there is
at least the impression of
two (or more) different planar structures existing instead of a single "fundamental plane" in which the spiral structure sits. But the interpretation of more than one disk seems quite secure for NGC 5084.
(compare, for instance, the "tilted or bent" Equatorial Dust Lanes seen in NGC 5078 and NGC 3628)
It is pretty easy, in theory, and also in practice (in the real universe), for gravitational interactions with another galaxy to warp or bend the Planar Disk Structure of a Spiral galaxy or S0 galaxy away from its principal plane;
in fact, in some cases, this sort of interaction can virtually "make spaghetti" out of the disk [this is, I think, what has happened in NGC 4438, which was probably originally an ordinary-looking edge-on S0 galaxy....in fact its bulge component (its spheroid) is
still normal, despite the
strong distortion of its outer regions. ]
However, in NGC 5084, we seem to be looking at (at least) two moderately-well-behaved disk structures, seen edge on, at two or more position angles.
If I had to gamble on what is going on here, I would put my money on the idea that the outer extremely-faint disk, which is not very settled in its appearance, is:
- still being formed (that is, it is coalescing under the influence of gravity)
OR
- being re-formed after being disrupted.
There are a small number of galaxies in which the outermost disk has been nearly-proven be currently in the process of
ongoing formation (this idea applies, probably, to M31 and our own Galaxy!). And this is a phenomenon that has been expected for a long time on theoretical grounds.
I might mention the NGC 5084 case to the brilliant Dr Kenneth C. Freeman of ANU, as he is an authority on the behavior of the planar components within spiral and S0 galaxies.
Best Regards,
Robert
"Just for fun and profit", here is the g+r+i band composite image from SDSS:
Attachment 137167
It would be interesting if the outer faint disk turns out to be "in the process of being formed" rather than a result of gravitational interaction with other galaxies!