Quote:
Originally Posted by ChrisM
Thanks Robert. Using my every-day DSLR is a quick and simple way of getting some results, even though they're not in the same league as others who are using LRBG and fast astrographs. I have limited my exposures to 60 seconds for now since the scope is not guided.
Chris
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Not so long ago, your "modest" image of N4945 would have been regarded as amongst the best. Imaging technology, and also the skill levels of those using the newest imaging technology, have been developing very fast.
NGC 4945 is very hard to figure out;
it is even more edge-on in orientation than NGC 253, so nearly all of the internal structure that is seen in images of N4945 is foreshortened and "one thing is on top of the other, due to the effects of our angle of viewing"
N4945 does seem to be later in the Hubble Sequence than is NGC 253 ( NGC 253 has an apparent Hubble classification of SBc, but it is arguably an SBb galaxy, which can be seen in infrared observations that remove much of the dust and confusion).
The multiplicity of assigned Hubble types in the literature for NGC 4945 (e.g. Sc, Scd, Sd) is an indicator that there is little to go on, as far as actual identifiable structure, at least when this galaxy is imaged at visible wavelengths. However, the significant amount of observed semi-chaotic structure could be telling us that this galaxy is closer to type Sd than to type Sc. Consistent with an assigned Hubble Type of Scd is evidence for very vigorous star-formation in this galaxy, as shown by the "feathered" appearance of the ionized gas in this H-alpha image from Jorn Rossa's 2001 PhD thesis; the ionized gas looks like it is being blown out of the disk-plane by the effects of multiple (hot, young, very luminous) OB stars!
This enigmatic galaxy continues to be something of mystery. Perhaps most instructive is the near-infrared image of NGC 4945 from 2MASS:
A reasonable interpretation of this NIR image is that this galaxy has two main spiral arms. I also have an 870 micron (sub-millimetre) image of this galaxy (which is a very low-extinction regime), and this image is also consistent with the existence of two primary spiral arms in NGC 4945. Note also the small, but very intense, central region of this galaxy.
(From images made at visible wavelengths, it is
impossible to say anything definite about the central part of this galaxy, due to heavy foreground dust within this galaxy)