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Viewing densities of galaxy positions - Printable Version

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Viewing densities of galaxy positions - selden - 05-30-2017

This is only marginal to OA since they won't be visiting other galaxies any time soon, but...

Here's my attempt to reproduce the SDSS image Orange Pie, using Celestia to view the results. The range in Z values is somewhat larger than the SDSS image, although the outermost whole green circle corresponds to the outer limit of theirs. Coloration is strictly by density, going from red for the least dense through yellow to white at the most dense.

I used http://skyserver.sdss.org/Casjobs to select galaxies in the appropriate RA and Dec ranges from the most recent SDSS data release, DR13, although I think they've only improved the processing of the data provided in DR7, not added anything new. The lower fan in the picture is "Stripe 82", the one which is used by the "Galaxy Zoo" project.

A Celestia "Addon" can be made available in a few days which includes this and some additional "fans" if anyone is interested.

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Here's a picture showing the entire dataset for the same regions.

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RE: Viewing densities of galaxy positions - selden - 05-31-2017

Sorry for the large image. The original is 1920x1080.

I've downloaded positions for about 1,700,000 galaxies as seen by SDSS in the northern hemisphere. I'm going to try making an addon that will let you select various layers and densities, but here are some views of them all.  It takes about 15 seconds of watching a white screen while Celestia loads its 82.5 MB binary CMOD on my laptop computer (1.6 GHz Core i7 with an SSD) but when that's finished, Celestia draws it at 60fps, with no lag at all.

In case it isn't immediately obvious, the upper right shows them while looking down from equatorial North, similar to my previous post. In the upper left, you're looking horizontally across the "front" face of the dataset, while the lower half of the screen shows how they're distributed on the sky in a wide-angle view as seen from the solar system.  One major problem is revealed in the upper-left image: using radial velocities as a measure of distance is rather difficult because there are extremely high variations in velocities within the larger, high density, galaxy clusters. This results in long, white (i.e. large velocity variations and high density) streaks pointing toward us. "Surely" there must be algorithms to help reduce this problem. Surely?

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