[madbadgalaxyman (Robert)]

Jason, This is my last post that is relevant to the appearance of your IC 5332 image.
Arguably, this discussion also belongs in the Science Forum. In fact, I will copy the posts on the dichotomy of spiral structure into the Science Forum so that the “science heavies” can consider them.

{{ Before I talk about science, I note that Gemini South Telescope recently released an image of this galaxy:
http://ausgo.aao.gov.au/contest2013/index.html
}}
"Gaseous young components of disks [a disk is the planar component of a spiral galaxy] (my italics) may be partially or even fully decoupled from the older disk population. As discussed by Block et al. (1994), the near-infrared spiral structure of galaxies often is quite regular and lacks multiple arms, indicating that higher-m modes of density waves are suppressed in the older stellar disk even if they are present in the younger component. The pitch angles (opening angles) of prominent near-infrared spiral structures may also differ from those of the optical spiral arms. "

- from D.M. Elmegreen et al., (1999), AJ, 118, 2618

The symmetrical two-armed structure in IC 5332 is remarkably obvious, though of low contrast.
In comparison, in many other galaxies which have (like IC 5332) a semi-chaotic structure of multiple knotty arms, a low-extinction near-infrared image is often necessary to "dig out" this spiral structure of the old stars, from the overlying dust and OB stars and HII regions and other young material.

A good explanation of the “duality” of the spiral patterns that can exist within a single galaxy, can be found in an article called “Shrouds of the Night – Galaxies and Rene Magritte” within the Conference Proceedings called “Galaxies and Their Masks : A Conference in honour of K.C. Freeman”
See google books, which enables access to part of this article:

http://books.google.com.au/books/abo...8C&redir_esc=y

(to find this article, search within the book for the title of this article, e.g. use the search terms “Shrouds of The Night”)
I quote here a few sections from this article by Freeman and Block and Puerari:
“Optically thick dusty domains in galaxy disks can completely camouflage or disguise underlying stellar structures. Cosmic dust grains act as masks or shrouds. (…….) Indeed the morphology of a spiral galaxy can completely change once the gaseous Population I disks of galaxies – the shrouds - are dust penetrated (…..)
From a dynamical viewpoint, the disk of a galaxy can be separated into two distinct components: the young gas-dominated Population I disk and the older star-dominated Population II disk "

In other words, two distinct components co-exist within the disk of a single spiral galaxy:

• According to authors Kenneth C. Freeman and David L. Block and Ivanio Puerari , the gas-dominated young disk of HII & Interstellar Dust & Cold Atomic Hydrogen & Molecular Hydrogen and OB stars is active and responsive and fast-evolving, because it is characterized by small random motions (it is dynamically “cool”) and it is prone to the Jeans instability (gravitational contraction into dense gas clouds, and thereby into new stars).
• In contrast with this young disk, these authors explain that there is also a distinct disk of “Population II” (= old) stars (which is the mass-dominant component a spiral galaxy), and that this old disk (and the spiral structure of old stars) may behave very differently from the young disk. This disk is dynamically warmer, and it has larger epicycles, and it evolves much more slowly than the young disk. The old stellar distribution in galaxies is sometimes touchingly referred to as the “stellar backbone of a galaxy”.
• The morphologies of these two components of a spiral galaxy may be completely different from each other.

In earlier articles by some of these workers, for instance (http://articles.adsabs.harvard.edu//...00137.000.html) and (http://labs.adsabs.harvard.edu/adsab...A...342..627B/) , it was shown that the multiple armed and knotty spiral pattern of a galaxy as viewed at blue and optical wavelengths , may be completely different from the much more regular spiral pattern that is observed in the distribution of its old stars ; In fact, a single spiral galaxy may have two very different Hubble types; an NIR Hubble type and an visible wavelengths Hubble type.
This contrasting “old stellar spiral” is often only revealed when an infrared image is made of a galaxy, so as to remove the overlying heavy dust distribution (which exists in some galaxies) and so as to make an image at a wavelength where more light is detected from the old stars within a galaxy.

(near-infrared light comes predominantly from red giant and red supergiant stars)
(The “old” spiral pattern in IC 5332 is mainly visible in the central part of this galaxy, probably because there is less confusion here with the dust and OB stars and HII regions that characterize the contrasting “young” spiral pattern)