This is my recent post copied from a thread in the IIS Imaging Forum, as I am starting a science thread about the structure and evolution of NGC 5128, which is
more affectionately known as Centaurus A. (what? emotion in a science thread?? )
(the imaging thread from which this is copied is
Centaurus A in UV by
sjastro)
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The three-dimensional morphology and evolution of the approximately disk-shaped "Extreme Population I" component of NGC 5128 (young stars + molecular hydrogen gas + dust) that manifests in our images as the dust lane, is a problem that has had a few different solutions in the professional literature. The most recent attempt was probably
Quillen et al., 2010, PASA, Vol.27, p.396 (in Proceedings of the Astronomical Soc. of Australia)
Here is the preprint of this paper......the preprint reference is arxiv: 0912.0632 (you have to pay for the final version!)
N5128__the disk__(arxiv 0912.0632)__Quillen +__2010_PASA__27__396.pdf
They have analysed a lot of the multi-wavelength imaging data about this galaxy and they fit a simplified model (or visualization) of the three-dimensional structure of the disk to these observations;
But they give their model in exclusively numerical terms, without a 3-D visualization of the structure that they have come up with. I may try to make a three-dimensional image of their model of the dusty disk galaxy that bisects NGC 5128, but I would have to find some tools to do so; typically, these 'tilted ring' models are usually made and displayed with the tools of radio astronomers.
The following near-infrared image from 2MASS (a composite of J and H and K bands) may be helpful, as it simplifies the structure of the dust lane by only showing the parts with the highest extinction:
Here is the inner disk of NGC 5128, in the central region of this galaxy, as imaged at 8 microns by the Spitzer Space Telescope: (8 microns picks up primarily dust emission, whereas 3 microns detects primarily stellar photospheres)
The disk is not planar, with a complex and warped/bendy structure.....this is a very complicated galaxy!
In the following image :
(1) The left panel shows a map of the two-dimensional distribution of the J-H colour (an infrared colour index) of this galaxy over the central parts of NGC 5128. The parts of the dust lane with the
heaviest dust extinction are displayed as the
lightest regions on this map. (This infrared colour map greatly resembles a negative of the dust lane. )
(2) The right panel shows a near-infrared (J band) image of the dust lane, displayed as a positive image from the 2MASS survey. (being infrared, it shows only the heaviest dust extinction). On this image are overlaid the
contours (isophotes) of the previously displayed 8 micron image from the Spitzer Telescope.
The above two images are from: 2006, ApJ,
645, 1092 (which is freely accessible on the internet)
( I am going to try to overlay this infrared disk with an image of the dust lane in the optical/UV regime, so you can get a better idea of where the infrared disk is located in this galaxy; I think there is a Herschel Space Observatory image that 'ties it all together' )
At present, the disk component that slices through the short axis of this galaxy is an unpopular subject for research; a search of the literature for recent papers about this galaxy using the
SAO/NASA Astrophysics Data System reveals that since 2007, as regards NGC5128, professionals have written only one or two papers about the disk component (dust lane) but
about 40 (!!!) papers about the orbital structures and kinematics and ages and metallicities of the objects in the spheroidal component, mainly studies of the very many globular clusters and planetary nebulae that belong to this galaxy ( these papers have the
still unrealised goal of characterizing the time-evolution of the spheroidal component.....the data archives contain massive data about galaxies, but nobody in the professional community has been smart enough to use it to produce a generally accepted theory of how galaxies evolve!! ).
Here is a section of a still useful (but somewhat out of date) comprehensive overview about NGC 5128, which came out in 1998 (F.P. Israel , Astronomy & Astrophysics Review, 1998, Vol.8, p.237)
N5128_the dusty disk.doc
(this is in MS Word 2000 .doc format)
The rest of this paper can be found at;
http://ned.ipac.caltech.edu/level5/M..._contents.html
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In the overall context of humankind's attempts to understand how galaxies evolve, this sort of observation and study of an individual case of galaxy merger and accretion can shed a light on how galaxies evolve and build up mass; NGC 5128 has previously undergone at least one
major merger (between two large galaxies) in addition to its recent "eating" of the smaller galaxy that produced the dust lane. There is also evidence that the big elliptical has swallowed a few other small galaxies!
In the 'hierarchical model' of galaxy formation, galaxy formation is
ongoing in today's universe, as smaller galaxies continue to merge with larger galaxies, while in another recently popular model of galaxy formation, galaxies continue to build up their masses (especially the outermost part of the disk component) by accretion of gas from the intergalactic medium;
we could be seeing both the "merger" model of galaxy evolution and the "gas accretion" model of galaxy evolution happening in NGC 5128, because the outermost portions of this galaxy (the 'ansae" at the two extreme ends of the long axis of this galaxy, as seen in Mr Sidonio's ultra-deep image) show evidence of
disky kinematics (orbits in the same plane, rather than in many different planes);
there seems to be
a disk forming in the very outer regions, which means that NGC5128 might even evolve into a spiral galaxy!
Here is a map showing the noticeably-elongated Disky distribution of (spectroscopically identified using OIII) planetary nebulae in the outer parts of NGC 5128, overlaid on a 2 by 2 degree DSS image. This image is taken from Peng, Ford, and Freeman (2004, ApJ,
602, 685 )
Is this a giant disk structure that is currently in the process of formation in the outer regions of NGC5128?
(it would require
infall of gaseous material for a 'traditional' gas+stars+spiral Disk Structure to form, but many giant elliptical galaxies
already have a kinematically cold disk-like component in their outermost regions)
The planetary nebulae have substantial orbital velocities, with line-of-sight velocities that can depart from that of NGC 5128 itself by over 100 km/s.(the rotational component is significant in comparison to the random velocity component)
The current "mild two-component S0 morphology" of NGC 5128 may be evolving towards a true Disk+bulge galaxy (becoming, eventually, a spiral galaxy or an S0 galaxy);
Peng & Ford & Freeman characterise the velocities in the outermost regions as "fast disk-like rotation along the major axis" of this galaxy, together with significant rotation along the minor axis as well. The strong rotation of the outer parts of this galaxy continues out to a radius of at least 50 kpc! ( 163,000 light years)
cheers
bad galaxy man