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Old 21-07-2013, 10:55 PM
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Abell 3574 (IC 4329 Group) - CONTINUED (from Observationsforum)

In the hope of spurring some further discussion.....
Here are some of the posts about the prominent IC 4329 galaxy group (also called Abell 3574), which is in the Centaurus-Hydra-Antlia supergalactic complex that also includes the Centaurus Cluster of Galaxies and the Hydra Cluster of Galaxies and the Antlia Cluster of Galaxies and The IC 4296 group of galaxies.

These posts are transferred from the visual observations forum:
___________________________________ _____

It seems to me that you are plainly seeing the stellar-like Active Galactic Nucleus of this galaxy; the edge-on disk galaxy IC 4329A has a very very luminous Seyfert Nucleus; one of the most prominent of these objects which are accessible to the amateur telescope.

Here is a picture of IC4329 and IC 4329A:

Attachment 143466

(this is an I band (800nm) image, displayed at a log scale so as to show both the central parts and the outer parts of these galaxies)

Here is a closeup of IC 4329A:

Attachment 143468

The central feature in IC 4329(a big elliptical galaxy), is also very bright;
as you perceptively remarked in your observing notes.
This is not a star-like central feature; so one wonders if it might be distinct from the rest of its host galaxy..... in terms of its structure, the ages of its stars, its rotational properties, and the orbital structures of its constituent stars.

The Hubble Classification of IC 4329 is 'probably an elliptical galaxy', but the vast distended envelope visible in photographs looks a bit like it might have disky characteristics; so if IC 4329 were a two-component "disk+bulge" system, it would be classified as Hubble type S0.

Of late, I have been leaning towards assigning IC 4329 to the S0 morphological class, albeit a "very mild S0 morphology"
___________________________________ __________

N5292 is an interesting and luminous outlier of the cluster; in this Galex ultraviolet image, there is a very large ring structure in its central regions that might accord with what you have observed:

Attachment 143835

[ Could look like a large diffuse annulus or ring, visually]

This must be one of the least known members of the population of (relatively) bright galaxies!

Blue 13th magnitude might not seem too bright for a galaxy, but considering the large distance of this galaxy, NGC 5292 is a most impressively luminous spiral.(at least comparable to M100 and M99 and M61, which are the first ranked spirals in the Virgo Cluster)

Actually, NGC 5292 might be as bright as B= 12.5 (large discrepancy between various catalog magnitudes)
___________________________________ _______

Some thoughts Regarding the distance of Abell 3574

The distance of this cluster of galaxies is usually given as 58 Megaparsecs (= 189 million light years), but mostly this distance has been derived using not-very-accurate methods of distance determination;
such as the Tully-Fisher relation and Velocity Distances.

This distance estimate could very easily be wrong by as much as 15 -20 percent (if not a little more).

In fact, the galaxies of Abell 3574 (= the IC 4329 group of galaxies) seem of remarkably large angular sizes compared to the angular sizes of the galaxies of the Centaurus Cluster of Galaxies (N4696, N4709, etc., etc., etc.) despite the fact that the Centaurus Cluster (= Abell 3526) is supposed to be significantly closer than Abell 3574.

At face value, it seems to me that Centaurus Cluster could be further away than is usually thought and/or Abell 3574 could be closer than usually thought.

The degree of resolution of the galaxies in Abell 3574 would be remarkable if it is nearly 200 million light years away. These galaxies seem to be too large and too easy to observe to be this far away!
(as a comparison, the Virgo Cluster is 50 million light years away)

The recession velocity of this cluster is often given as about 4870 km/s in the CMB reference frame, a velocity which also yields a very large distance, for plausible values of the Hubble Constant. However, I note that Richter in 1984, A&AS, 58, 131 gives only 4253 km/s as a mean velocity of this cluster (corrected to the centroid of the Local Group).
So there can be a lot of error in estimating the true cosmological velocity of a cluster of galaxies. (not forgetting that there is a 1500 km/s peculiar velocity in the line-of-sight of one of the subclusters of the Centaurus Cluster!)

In general, the IC 4329 group is remarkably poorly known and studied compared to similar clusters in the Northern sky!!
___________________________________ ___________

The 'star' at the centre of IC 4329A appears to be a bona fide Active Galactic Nucleus located within its host galaxy. (Dr William Keel says so, and he is an AGN expert.)

I therefore assume that it has been spectroscopically identified as such (same redshift as its host galaxy, very very Strongly Broadened spectral lines, etc.)

"A Catalog of Quasars and Active Nuclei" by Veron-Cetty and Veron, classifies the nucleus of IC 4329A as being a Seyfert 1 nucleus.

IC 4329 itself seems to have some sort of very-bright central feature, but this feature is diffuse in appearance; the central profile (at small galactocentric radii) of increasing surface brightness vs. decreasing galactocentric radius..... is very steep in this galaxy.
___________________________________ ___________

Dana posted the following;
Based on what Patrick observed and Robert wrote, you have chanced on a very interesting galaxy pair that the professionals have analyzed only perfunctorily.
IC 4329A has such a bright core that as recently as 1979 it was identified as a quasar. (There is a nearby quasar, but adjacent to IC4329A and far more remote.)
Today, as Robert says, it’s known as a highly luminous Seyfert (Lx=6×10^43 erg s-1). Only one recent paper (2012) barely mentions IC 4329 itself in passing, and a 2009 Harris paper is devoted to the not particularly remarkable C-M properties of 4329’s globular system. All the rest of the 15 papers about this pair trail backwards from 1998 back to the 1970s.

I wonder if Patrick might have another look at both these galaxies’ cores again to see if IC 4329 has a softer stellar appearance compared with IC4329A. His original observation of July 1 said as much; I’m wondering if a second look would reveal any more.

As for its neighbour IC4329A, its hot AGN core and has two powerful magnetic fields parallel to the disc. This 1995 paper says: ‘The edge-on dust lane of IC 4329A shows significant levels of polarization oriented parallel to the lane, which suggests that there is a magnetic field in the plane of this galaxy which is uniform on kpc scalelengths. Although the Seyfert 1 nucleus is seen through the polarizing dust lane, it appears to have an additional, intrinsically polarized component with a position angle approximately parallel to the galactic plane. We suggest that the intrinsic nuclear polarization arises from dust scattering in an asymmetric geometry, possibly involving an inner torus, surrounding the central AGN. The relative orientations of the axes of the AGN and the disc of the host galaxy may have been influenced by a recent interaction between IC 4329A and its massive neighbour IC 4329.’

http://heasarc.gsfc.nasa.gov/images/...ies/ic4329.gif
Above is an image to show what they mean about the xray corona and intragroup shock-front bubble.
___________________________________ ___

Dana wrote:
I see that IC4329 is variously identified as a lenticular (S0) and an elliptical (SIMBAD merely IDs it s ‘Es D’. I’m not sure what ‘Es D’ means, either.) Robert has been writing quite a bit about S0 lenticulars lately and I think he’s right in two ways about this pair: (a) 4329 looks like a small-bulge, large-disc S0 and not an E, and (b) the pair are closer than their stated 59 Mpc

Bad Galaxy Man replied:
The "D" simply refers to an elliptical which has a very extended and extremely-faint envelope around it.
(but real "D" galaxies, however, have outermost halos so faint that they can be invisible in standard imaging. These halos have a tendency to merge eventually with the intracluster light (which is composed of stars that float in between the cluster galaxies)

The old definition of an S0 galaxy is simply that the apparent two-dimensional image of a galaxy (necessarily it is a galaxy with very-smooth light) has two components; the central component which has a fast falloff of surface brightness with increasing radius , and the outer component which has a shallow falloff of surface brightness with increasing radius.
Thus, this traditional definition of an S0 galaxy says nothing at all about what an actual galaxy is, in three dimensions.
In other words, we might assume that the central component is a spheroidal bulge and we might assume that the outer component is a rotationally-flattened & planar disk; but this does not have to be the case.

In the new systems of physical galaxy classification, we focus more on what is actually going on within the three-dimensional 'real' space of each galaxy;
so an S0 Galaxy is today redefined as a galaxy having a bulge component plus a disk component, plus it must also have a Star Formation Rate and a Cold Gas Content intermediate between what we find in elliptical galaxies and what we find in Sa galaxies.
In any galaxy with two apparent components, the radial falloff of surface brightness and the shapes of the isophotes of both the apparent "bulge component" and the apparent "disk component" are amenable to numerical measurement; so by making these measurements we can better assess whether or not a galaxy with two apparent components really does have a genuine disk component and a genuine bulge component.
(Disks and bulges are today very strictly defined in terms of shape, surface brightness falloff, stellar orbits, etc.)

IC 4329 is an "apparent" S0, as are good numbers of galaxies often classified as ellipticals. But whether or not the outer component is a real disk is something that cannot be decided from mere inspection of a two-dimensional image.

Isophotes (= the elliptical lines of equal surface brightness) within an elliptical galaxy can change their shapes in a complex way, with progressively changing (increasing or decreasing) galactocentric radius;
sometimes the isophotal ellipses get a bit pointy, which is often a sign of a low-surface-brightness disk component, while at other times the isophotal ellipses look markedly "blocky" (somewhat rectilinear) which is more likely to be the sign of a slowly-rotating component with little angular momentum and with stellar orbits in many different orientations.
___________________________________ ____________

Last edited by madbadgalaxyman; 23-07-2013 at 08:30 PM.
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Old 23-07-2013, 05:31 AM
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Weltevreden SA (Dana)
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IC 4329 & -29A data

07/21/2013:

Robert raises a host of very interesting points with this new thread. His post will have us ransacking the databases for weeks. I also thank Patrick again for making the original observations in enough detail that we all await the end of the bright moon cycle to chase after these goodies ourselves.

Robert is certainly right that we don’t have enough data to say anything very certain about the IC 4329 distance—especially his point about the Tully-Fischer’s uncertainties in instances where a galaxy’s disc rotation curve can’t reliably be determined. Robert, could I ask how much is certain about the disc rotation rates of S0s in general and whether line-of-sight (LOS) position angle affects rotational power-law distributions the way it does ellipticals? I notice that we don’t have any recent bolometric or spectral energy distributions for either of the pair. We also don’t have enough absolute motion data—we know the pair is receding from us at redshift z=0.01689, but that is line-of-sight or 3-D reference frame? The data sets are too imprecise to determine what angular velocity components exist, and along which axes. Said another way, we can’t parse Doppler reddening from recessional reddening. For that matter, we don’t have intergalactic medium reddening, either.

There are a couple of other worthy lines of analysis than can help us determine whether Robert’s basic point—eyepiece angular size and brightness evidence as we observe it gives one to believe this pair is closer than its literature data say. I think all of us could take a visual look at these two and compare their apparent sizes with other Cen/Norma galaxies of the same visual magnitudes. I’d love to know what Patrick’s second look will tell us after reading all this stuff. IC 4329 is vm 11.54 and 3.2 x 1.6 arcmin; and IC 4329A’s is vm 13.1 and size 1.3 x 0.4 arcmin. Sad for me, by the end of this bright moon cycle these galaxies will be getting rather low in the sky. They won’t give me much to work with due to my aperture limit of 200mm. Patrick, could you have another look at the estimated size of the 4329 core region? Does your 30 arcsec estimate still hold?

IC 4329A’s AGN core radiates at such high UV and xray luminosity that its absolute bolometrics must be devlish to measure. The AGN is certainly hot—this 2009 A-J paper states that the AGN has an active 130-million solar-mass black hole which is the source of the AGN’s high energy yield in the 10-30 KeV xray band. The 10-30 KeV strength/distance ratio point to a Hubble redshift of z = 0.01605, which correlates to a comoving radius of 71 Kpc.

Robert’s querying the real distance of the Ab3574 cluster raises the issue of how quickly data becomes dated as new and better measuring equipment comes on line. Much of the Ab3574 data dates from the late-1990s back to the 1970s—15 to 40 years ago.

There are a couple of workarounds to this dilemma. One is the absolute magnitudes and metallicity functions of globulars associated with either of the pair. The GC metallicities of IC 4329 have been studied as recently as Harris et al 2009. In general, GCs fall into three age bins: two-thirds are >10*Gyr, one-third are between 5 and 10*Gyr, and a small fraction have an age <5*Gyr. Most GCs are bimodal—they consist of two generations—a primordial very low metallicity one (metal-poor), and a second population roughly 200 Myr younger. The 1st generation is called a ‘red’ GC because it is slightly older and hydrogen-rich/metals-poor. The 2nd generation is higher in iron and the alpha elements because its stars were formed out of the SN 2b core-collapse and SN 1a white dwarf supernova of the first generation. The 2nd gen is called a ‘blue’ GC because its stars tend to be lower-mass and less evolved on the main sequence; this would mean a high abundance of stars under 0.8 solar masses. A globular regeneration cycle typically takes 200 Myr. There is usually no 3rd or later generation because the supernova cycle and hot AGB stellar winds of the 2nd generation eject nearly all remaining starforming gas. (The GC NGC 2808 has a third & bluer main sequence, which has GC folks happily scratching their heads and plotting scope-time strategies.)

Earth-bound and orbital spectroscopy have really taken off since around 2006. Grating resolutions have gone from 25,000 to 46,000 in that time, and signal-to-noise ratios are now 120-to-1 instead of the 40-to-1 of a decade ago. We have ROSAT and GALEX these days. With a cluster as remote as Ab3574, astronomers need ever photon they can get because metallicity bimodality depends on the accuracy of colour bimodality. Colour bimodality data depend in turn on the magnitude differences between the red giant branch and the red clump (the red end of the horizontal branch), and the magnitude difference between the blue horizontal branch and the main sequence turnoff point. A GC bimodality difference of Δ(B – I)≈0.3 would correspond to age differences of 4.5 Gyr and 7.5 Gyr for metallicities of [Fe/H] = –2.25 and –1.5, respectively. If we know the above red/blue magnitude data, we know the GC absolute magnitudes from which to calculate their distances.

A typical GC has a half-light radius of 3 pc (a bit under 10 light years). A GC at IC 4329’s estimated distance of 58 Mpc would subtend an angle of 0.02 arc sec, which is smaller than the earth-based scopes’ pixel resolution even on nights of superior seeing at 0.5 arcsec or better. The Hubble Wide-Field/Planetary Camera resolves to 0.01 arcsec, but all that means is a 2-pixel dot instead of a one-pixel dot. In our best equipment IC 4329’s GCs still appear star-like. All we can do is measure their blue-to-red ratios. Hence we have poor spectral distribution numbers for the IC 4329 pair. Here’s the problem in graph form, based on 2006 data from the Gemini-South GMOS camera (Cockcroft, Harris et al, Astronomical Journal 138 (2009) 758):

The dotted boxes in Image 1 below [Figure 2 in the linked Cockcroft-Harris article above] show us the sampling limits of IC 4329’s globulars. The sample consisted of 3558 de-contaminated and then measured objects. Instrument error sharply limits the data set to the small sample within the dotted boxes. The vertical scale is the important one in this graph: it basically puts an error limit on data reliability at one-tenth of a magnitude.

In Image 2 attached [Figure 4 in the Cockcroft-Harris article] is where the IC 4329 globulars lie on a normalised line radiating from the core to the instrumental limits of observation. The dotted vertical lines demark the inner zone of reliable data, de-noised for proximity to the galaxy core, and the outer zone where field objects contaminate accuracy:

Even constrained like this, some C-M diagram data can be extracted from this data. Image 3 below [Figure 3 in the article] shows three CMDs of galaxies with similar brightness and distance properties, one of them IC 4329. The objects in the dotted boxes are the 3 galaxies’ globular clusters binned by colour and brightness.

And finally (drum-roll, please), Image 4 below [Figure 6 in the article] is the resulting CM diagram, plotted as bins of the g (green-visual 551 nm) minus i (infrared 806 nm) colour bands. The vertical measure is luminosity and the horizontal measure is colour band.

In this plot, the upper set of large squares are the measured blue (lower metallicity) population and the bottom squares are the red globular population. (The lines are means lines for various interpretive calculations for the globulars not important to us here.)

All of this sheds light on the interpretation of IC 4329 as a S0 galaxy with a spiral-like GC distribution. In general, spiral GCs are more alpha-enhanced in the halo (more SN 2b contribution) and iron-group enhanced (more 1a contribution) towards the core. This points to a spiral ancestry for the S0 IC 4329, but it doesn’t help us determine how far away IC 4329 is, or its combined vector motions within the Hubble Flow.

IC 4329’s globulars have a mean recessional velocity of 4808 ± 21 km/sec in the CMB reference frame. That would locate Abell 3574 as a member of the Hydra-Centaurus Supercluster. But we knew this already, so all we’ve done here is go to considerably lengths to eliminate IC 4329’s GCs as concluding anything either way with regard to Robert’s point. (It was fun, though.)

A second line of reasoning is related to the black hole in the core of IC 4329’s recently interacted neighbour IC 4329a. The two galaxies had a grazing brush with each other, the xray remnant of which is a hot spot in a bridge between the two:

Note that in Robert’s image of IC 4329A, there appears to be slight deformation of the outermost part of the visible disc, bending at the tip CCW in the direction towards 4329 itself; there is a somewhat less noticeable deformation of the upper left part of the disc as well. (The whole thing looks like a skinnier version of the Integral Sign Galaxy.) An ancient galactic graze would not boost our knowledge of the galaxies’ present distance, but it adds to our evidence whether IC 4329 is an S0 or E. A shallow graze would add no net globular accretion to either galaxy (though a few might change hands), since the mass-metallicity relationship of ellipticals is sharply weighted to the blue due to gas impoverishment during and after an elliptical’s formation. The Milky Way’s MMR is red-rich and blue-poor; it still has plenty of gas for new, metals-enhanced star formation. One argument in favor of NGC 104, the Sombrero, being an S0 with a disc is that it has a blue MMR (Rhode & Zepf 2004). OTOH, M49 has no blue MMR and astronomers have no explanation (Strader et al. 2006). Go figure.

I wonder if a higher-rez image would reveal IC 4329A to be a warped remnant of the long-ago interaction. The comparative modesty of the warp with respect to the mass of IC 4329 points to a barely grazing or non-touching disc-disc interaction. The elevated-luminance bridge evident in the ROSAT image traces the path hot gas and railing stellar streams would take. Add that info to IC 4329’s blue-weighted GC population and I wonder whether we have in the IC 4329 pair an example of interaction disturbance turning a spiral turning into an S0.

The upshot of all this is that we need better, more modern data. It would be helpful to know (a) Na/O anticorrelation, CN correlation, [Mg-Ti/Fe] ratios from SN 1a contributions; and (b) Cr/Ni/Ba abundance and r-process neutron-capture abundances from Type 2b supernovae.

Unless Robert knows someone with access to Hubble or ESO proposal-vetting committees, we’ll probably be waiting awhile.

Wish I had a bigger scope. Two meters would be nice. Couldn’t afford the upkeep. Pity.

Thanks again to Robert and Patrick.

=Dana
Attached Thumbnails
Click for full-size image (1 IC 4329's instrumental error, Harris 2009.gif)
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Click for full-size image (2 IC 4329 C-M diagram, Harris 2009.gif)
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Click for full-size image (3 IC 4329 globular radii from galaxy core.gif)
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Click for full-size image (4 IC 4329 red and blue populations.jpg)
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Old 23-07-2013, 08:41 AM
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madbadgalaxyman (Robert)
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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

Last edited by madbadgalaxyman; 23-07-2013 at 09:08 AM.
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Old 24-07-2013, 10:08 PM
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IC4329 group- do numbers lie? Also pix of IC 4329 .

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 View Post
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.
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)

(2) 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.

Click image for larger version

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Click image for larger version

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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

Last edited by madbadgalaxyman; 26-07-2013 at 08:49 PM.
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