[madbadgalaxyman (Robert)]

Very Good research, Dana!

Could you clarify or restate your question about the Tully-Fisher relation?

I have plenty of good imaging material on hand for IC 4329, so stand by for more "pretty pictures" of this galaxy in this forum.

Incidentally, the bending/twisting/warping of the disks of edge-on galaxies is something I understand very well; so I should be able to make an informed comment about the nature of the warp you have reported in IC 4329A.

In the 1990s, I used to visually observe the Centaurus Cluster and IC 4329 cluster and also the Antlia Cluster and the Hydra Cluster, so my comment about relative distances of these galaxy clusters was just a "practical" comment in response to the obvious differences in the relative sizes of the galaxies, when comparing galaxies in the various clusters of galaxies.
Also, it deserves emphasis that the "Cen 45" component of the Centaurus Cluster has a confirmed 1500 km/s peculiar (individual)(non-cosmological) motion in the line of sight; so its velocity distance is way out from its actual physical distance.

In my experience, the GCLF (globular cluster luminosity function) method of distance determination, works somewhat more accurately than the TF method.....the peak of the Luminosity Function of the populations of globular clusters belonging to many and various galaxies, is nearly always the same absolute magnitude. We should write to William Harris about this; I am sure that he has already calculated a GCLF distance for IC 4329. (I have a nasty feeling that Harris is now semi-retired.....this is not good, because he is a man who "really knows globulars" almost "face-to-face", from a lifetime of studying them). We can also do a distance calculation ourselves for this galaxy, if we know the LF of the IC 4329 system of globular star clusters.

My own current project is to analyze the isophotes, colours and surface brightness distribution, of IC 4329.

So here is a quick writeup of where my own research is leading.....

Over the years, I have pondered the unusual shape of the outer "envelope" of this galaxy, from time to time, and my earlier thoughts that there is something unusual about this galaxy are probably correct:

In fact, in terms of the distribution of surface brightness over the face of this galaxy and the shapes of its isophotes (the elliptical lines of equal surface brightness), a lot of things are "not quite normal" about this galaxy. IC 4329 is probably not an S0 galaxy because the peculiar outer envelope is not disky in appearance, neither is it really an elliptical galaxy because of its unusual morphology.

This is why a lot of qualified professional galaxy classifiers give it the "sitting on the fence" Hubble Type of E-S0, which is just a heterogeneous collection of galaxies which are less compact in appearance than Ellipticals but more compact in appearance than S0 galaxies.

IC 4329 is yet another example of an allegedly "Elliptical" or "S0" galaxy which could well be "off the standard Hubble Sequence!
(( e.g. NGC 1316 and NGC 5266 and NGC 5128 are all so-called "elliptical galaxies" which cannot be assigned to a single unique hubble type! Repeated merger or accretion may produce a galaxy which is not an S0 and not an elliptical, instead producing a galaxy which is a "something else"....in other words, a novel morphological class which is not on the orthodox sequence of Hubble types)

Given that there are fairly prominent shells visible in high quality images of IC 4329, and that its outer envelope looks very unusual [[ there is an extended "S0-like" distribution of light which is not really shaped like a disk; in fact, its shape is distinctly blocky (somewhat rectilinear), which is more indicative of low rotation and stellar orbits in various orientations! ]], I thought I might look for possible anomalous broadband colours in the Hyperleda database.....

The apparent B-V colour of this galaxy is 0.9, which is very very blue for an elliptical galaxy of high luminosity!!(you can do an SQL search in Hyperleda to isolate galaxies with various properties of colour, size, luminosity, type, etc. )

At face value, this blue color, plus the unusual optical morphology, are consistent with the idea that this galaxy has most likely undergone mergers with smaller galaxies, leading to a substantial proportion of its total light coming from younger stellar populations.
(comparison: in NGC 5128 there is evidence that the overall galaxy was produced by a major merger between two large galaxies, and there is also evidence for the more recent cannibalization of several smaller galaxies)

cheers,
galaxyman