Dear Galaxy friends,
(1)
Paddy had an interesting comment in the recent Visual Observations forum; he too thinks that the visual obviousness of the galaxies in this cluster of galaxies is such that they are too big and bright to be 190 million light years away:
Quote:
Originally Posted by Paddy
What you say about the distance makes sense to me Robert, as the galaxies do seem too easily observed for nearly 200 million light years.
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The prevailing distance estimate for Abell 3574 is
nearly four times the Virgo Cluster Distance. However, this is an average of several Tully-Fisher distance estimates for individual disk galaxies within the cluster; and each T-F estimate has a nominal error budget of 20 percent (to one standard deviation).
But actually looking at the galaxies, one finds it hard to believe that the distance of this cluster could be greater than two to three times Virgo Cluster!!
Indeed, this does seem to be a case where several "heavyweight" astrophysicists have determined the distance to this cluster of galaxies (indeed there were two very recent re-determinations of the cluster distance using the Tully-Fisher method)
yet the results of all this "heavy number crunching" are greatly at odds with the (admittedly subjective) evidence of our own eyes!!!
Alan Sandage, who died not long ago, was a very Great extragalactic astronomer who "really knew" galaxies, in an almost face-to-face sense. He definitely was able to make reasonable estimates of the relative distances of various clusters of galaxies and groups of galaxies, using only simple parameters such as the angular size of a galaxy, the surface brightness of a galaxy, and its degree of resolution. A good example of this was when he was able to accurately pick those galaxies which are in the foreground or background of the Virgo Cluster of Galaxies, using these simple "eyeball" techniques. (Sandage also correctly estimated that NGC55 and NGC300 are much nearer than NGC 247 and NGC 253, thus correctly estimating the true structure of the Sculptor Group, well before more precise measurement techniques were applied)
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Pretty Pictures of IC 4329
Here are some images of IC 4329, from the Carnegie-Irvine Galaxy Survey. I applied an unsharp mask, and two or three of the shells in the envelope are now visible.
It is easy to understand, from contemplating these images, why this galaxy has often been classified as an S0 galaxy rather than an elliptical galaxy.
Indeed, the initial precepts of the Hubble galaxy classification system mainly classified only the structure of the
image of a galaxy rather than the
actual structure of the three-dimensional galaxy itself, and there do
seem to be two very-smooth components in the image of this galaxy, which is typical of a galaxy of the Hubble type S0.
However, as per my previous post, I think the structure of this galaxy is too complex and unusual to allow its easy placement somewhere into the standard Hubble Sequence of
E - S0 - S0/a - Sa - Sb - Sc - Sd - Sdm - Sm - Irr