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PostPosted: Thu, 16-07-15, 13:12 GMT 
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Joined: Fri, 31-08-07, 7:01 GMT
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Hi all,

unlike spiral or elliptical galaxies, irregular galaxies are lacking an approximate symmetry axis. This fact renders their display much more challenging a priori. Thus a new kind of approach seems to be needed for a fast CPU/GPU-based visualization of all available catalog data about irregular galaxies.

About one year ago I was experimenting with the so-called Diffusion Limited Aggregation (DLA) algorithm, viewtopic.php?f=11&t=628, that may efficiently generate flexible irregular fractal structures of dots in nd = 2, 3, 4 dimensions, quite suitable for the present task. Not to forget...there exist numerous manifestations of DLA in Nature! Like for spiral galaxies, the initial DLA dot patterns are then associated with sprites using fast GLSL shader code. With various smaller modifications I have now subscribed to this approach.

To give you a flavor of the current status, I compiled below a small "gallery" of rendered irregular galaxies. For comparison of the results as to shape, color, orientation and position relative to bright stars, I have mostly added a small blue-framed image containing real photos and a grid with identical orientation as the visualized images that exhibit a much higher resolution, however. Note, all visualizations are entirely done by computer...i.e. no human interference taking place!

There is a handy tool in the CDS Strasbourg data center,, called Aladin. Aladin is an interactive sky atlas. It optionally displays the entered deepspace objects properly alligned wrto a grid, with North pointing up and East to the left. This way catalog entries like shape, orientation, color, position relative to bright stars etc may be judged immediately and accurately! The corresponding Aladin displays are shown in the mentioned blue-framed small "sub images". Since the available photos about irregular galaxies and irregular Dwarfs are often not very good, I have skipped these comparison images in some cases.

When looking at the "gallery" below, it is crucial to always use your maximum possible display size!

Always click first on the image. If the cursor shape shows a "+", click again twice onto the image, such that the cursor first becomes a "-" and then once more a "+". Finally hit the browser's fullscreen key shortcut. For Firefox this would be the F11 key! . For returning to the next image, hit again F11 and then the browser's backward arrow "<=".

The native size of most images is 1920x1200 pix

The pink regions are to indicate starforming HII regions. This feature is presently only qualitative, since precise data are still lacking.

Note: the overall colors are strongly correlated with the global B-V color index: small B-V ~ 0.2 ..0.35 corresponds mostly to bluish galaxies, while large B-V ~ 0.45..1.0 amounts to increasingly orange/brown galaxy colors! Many irregulars have smallish B-V.

We start with a neat close-up:
ddo64_23062015_2.jpg [ 171.87 KiB | Viewed 6329 times ]

ddo68_dla4.jpg [ 136.88 KiB | Viewed 6329 times ]

ddo78_dla4.jpg [ 66.06 KiB | Viewed 6329 times ]

Watch the position/orientation of ddo 82 relative to the 3 very bright stars.
Also larger B-V ~ orange/brown galaxies. The photo has a touch of dark orange, actually.
ddo82_dla4.jpg [ 185.06 KiB | Viewed 6329 times ]

Watch and compare the orange-blue colors of the bright double near the image center
dw1_mb3_doubleStar_dla3.jpg [ 229.57 KiB | Viewed 6329 times ]

eso_245-5_dla4.jpg [ 165.26 KiB | Viewed 6329 times ]

A very bright star in correct location!
ic5152_dla4.jpg [ 200.48 KiB | Viewed 6329 times ]

The Large Magellanic Cloud (LMC)!
lmc_dla3.jpg [ 129.07 KiB | Viewed 6329 times ]

ngc2326a_ngc2326_dla4.jpg [ 162.74 KiB | Viewed 6329 times ]

Finally, a spectacular view by an observer, located close to the rich globular NGC 104, onto the Small Magellanic Cloud (SMC)
ngc104_background_SMC.jpg [ 454.69 KiB | Viewed 6329 times ]



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