madbadgalaxyman
21-07-2013, 11:55 PM
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:
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:
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:
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 (http://adsabs.harvard.edu/abs/1995MNRAS.276..460W) 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/objects/galaxies/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.
___________________________________ ____________
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:
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:
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:
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 (http://adsabs.harvard.edu/abs/1995MNRAS.276..460W) 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/objects/galaxies/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.
___________________________________ ____________