The NGC899/IC 223 pair
I would like to mention a pair of very interesting galaxies that are near in the sky to NGC 908.
NGC 899 and IC 223 are pair of galaxies separated from each other by 4.9 arcminutes, and
both of them have some strange aspects to their structures.
This (probably) physical pair of
unusual galaxies is just over 30 arcminutes from NGC 908, and the redshifts (recession velocities) of
all three galaxies are so similar that they are very likely to belong to the same physical grouping of objects.
NGC 899 is the larger of the two galaxies, at some two arcminutes across and Blue magnitude 13, though it should be said that catalog magnitudes and dimensions of peculiar objects are more likely to be inaccurate.
Here is a Blue + Red wavelengths composite of two DSS images of this pair, taken from the Aladin virtual telescope:
The upper of these two galaxies is IC 223 and the lower is NGC 899. On this image, they both look a little odd, and there is a trace of interesting knotty material outside the main optical body of NGC 899.
If we now look at the version of DSS at
http://server1.wikisky.org (which is very contrasty), the image of NGC 899 begins to look very interesting indeed:
In this image, there is
probably a definite detection of a good number of small knots outside the main body of NGC 899.
One could call this an irregular galaxy, but really it does not resemble any normal irregular galaxy!
Now when I used the GalexView virtual telescope (on the internet) to bring up the GALEX satellite (Far Ultraviolet plus Near Ultraviolet) image of these two interesting galaxies, I got one hell of a surprise......
IC 223 (the smaller of the two galaxies) seems to have a strange FUV emitting region (FUV displays as blue) well outside of its main body.
And NGC 899 looks
extremely strange in ultraviolet light; it has far-ultraviolet emitting knots arrayed in a
very odd pattern that looks like it might conceivably be unusual arms that surround a disky main body. These knots are, on the balance of probabilities, likely to be giant knots of very luminous OB stars, but other explanations cannot be excluded.
Here is the GALEX ultraviolet (color coded composite of FUV + NUV) image of these two galaxies:
It could be a hard job to pick up the knotty material surrounding NGC 899 in amateur images....it is faint in optical images!
(the Far-ultraviolet regime is
extremely sensitive to even modest amounts of blue/ultraviolet emitting material!)
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The unusual Outer Arm of NGC 908
The "upward bending" (or downward bending!) of a spiral arm in NGC 908, as mentioned in PeterM's interesting link, is an interesting phenomenon in some spiral galaxies.
It is more obvious in blue-sensitive images of this galaxy, as the dust distribution in this arm is also peculiar:
(this is a B-band (blue) image of NGC 908 taken from a survey known as OSUBSGS)
A similar phenomenon is seen in a good number of spiral galaxies, but it is easy to miss it if you aren't alert to the possibility that an arm could
bend away from the principal plane of a galaxy.
( Apparently, even our own Milky Way Galaxy has an outer spiral arm that is not exactly in the same plane as the rest of our Galaxy.)
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P.S.
As mentioned in my previous post in this thread, NGC 908 is likely to be very comparable to the giant Virgo Cluster Spirals M61 and M100. One more piece of evidence for this assertion is that the measured maximum Circular Rotational Velocity of NGC 908 is similar to that of M61 and M100.....which is a strong indication that these three galaxies are of very comparable mass.
[[ R.B. Tully's "Nearby Galaxies Catalog" gives rotational velocities (which is a mass estimator) for nearly the entire population of spiral galaxies within 3000 km/s ]]