Friends,

the other day there was a fairly extended dispute at the shatters.net forum between the user Cham and myself, concerning Celestia's official database of 10937 galaxies that I have prepared and thoroughly tested over a number of years (deepsky.dsc).

Discussion with Cham

Cham's reproach was about the existence of conspicuous straight line "strings" of galaxies in his 3d display of (RA,DEC, Distance). The strings would correspond to roughly fixed angular directions (RA, Dec about constant) and extend significantly in distance.

For quite a while, Cham advertized these striking patterns as strong artefacts in my database.

However...

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In my view, these "strings" of galaxies were (mostly) NOT artefacts, but rather signatures of the onset of the famous large scale filiaments that are so conspicuous in the Sloan DSS data at higher values of the redshift z.
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Since our discussion turned out to be quite constructive (despite sometimes "heavy" disagreement, initially ) , I thought this thread at CelestialMatters would be a great place to continue with increasing emphasis on Cosmological issues!

As a major argument in favour of my view, I presented part of the famous conformal Princeton plot of the Universe, from here
Princeton Plot
based on the great original paper
Princeton original paper

Let me recall the lower part of this amazing display of ALL known data in RA vs. log(distance). It reaches up in distance where the large scale filiaments from Sloan SDSS, become very conspicuous. You notice the various galactic clusters like the Coma cluster etc.



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The crucial features I want you to focus on are these obvious straight vertical lines of galaxies (blue dots) for CONSTANT RA rising up in distance until they merge continuously into the more complex filiamentary structure of the SDSS data!!! This shows without doubt that these vertical streaks in distance for constant RA are there and that they are physical with high probability.
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Here is once more a 3d plot by Cham of Celestia's galaxies, with the highly elongated Virgo I cluster emphasized in red. A ray in this plot corresponds of course just to CONSTANT RA like on the "conformal plot".



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Now let me turn to some interesting new stuff:
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I used Celestia's official database and printed out ALL galaxies versus (RA[hours], distance [ly]). Then I plotted them in the same way as the Princeton plot above (, using Maple 12 and semi-logarithmic axes). Here is the result:


(Click for a bigger image!)


Along the horizontal axis I again plotted RA [hours] and vertically the decadic logarithm of the distances [ly]. Each blue dot you see is a Celestia galaxy. In this way of displaying, one can again clearly see the vertical strings of galaxies besides some conspicuous horizontal structures. Note the structures around 12 h (Virgo cluster!)
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There is a very nice qualitative agreement of these vertical streaks at fixed RA values with the original Princeton plot.
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An important next step is to add in the data from the finalized Sloan DSS that may be downloaded from here: http://cas.sdss.org/astro/en/tools/search/SQS.asp

Cham already produced some beautiful conical plots, e.g.

(Click for bigger images)



nicely merging in with Celestia's database (as he noted ). It would be even more instructive to add the Sloan data into my above plot of (RA vs. log10(distance)). This way the continuation of the vertical streaks into the Sloan filiaments could be best demonstrated. This will certainly come soon.

Fridger

Keep it going there Good Doctor...
Trying to force these concepts into my impaired neurons, but is very interesting to watch as it develops here.

Friends,

It's now time for some further exciting cosmological discussion!

But first let me apologize in the following

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Prolog
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Yesterday night, I have displayed in this post a number of exciting comparison plots between the Celestia galaxy database (deepsky.dsc) that I have prepared and tested over years, AND the finalized Soan DSS (DR6) galaxy data for z<1 and 0<RA<24h.

Unfortunately after a lot of work, a really STUPID conversion error of parsec to light years had crept into my Perl script for the conversion of the Sloan data! That respective conversion factor pc2ly = 3.26167 had accidentally appeared TWICE in my Perl script , hence all my galaxy distances for the Sloan DSS data were too large by that factor 3.26167!

Fortunately, Guckytos aka Christian was far more attentive than me tonight, and wrote:



I immediately replied this and started to work !



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It only took a few minutes, until I had spotted that stupid error of mine. But I had to redo all the plots of yesterday. In order not to generate a plot inflation here, I have decided to EDIT my post of yesterday, rather than add the same long story again with corrected Sloan distances!
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So here we go...


As promised , I meanwhile read out ALL 335 096 finalized Sloan DSS galaxies (DR6) for z<1 from their server.

Here are some respective hints, if you want to do this yourself:
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The SDSS URL is : Sloan Digital Sky Survey (SDSS)

From here I suggest, you go straight to the direct SQL interface, SQL query interface

which is fastest and MOST general, as to placing special options. Learning a bit of the SQL database language is really easy, given the many examples and a nice tutorial on the Sloan site.

Here is my small SQL scripting code that I pasted into the SQL console to read out all these great Sloan data:



What does that mean?

In SQL there are these 3 crucial keywords: SELECT, FROM and WHERE


SELECT specifies the variables you want to include on return, in our case ra, dec (in decimal degrees) and the redshift z.

FROM specifies the dataset objects that we want to query: SpecObj s contains all spectroscopic data, notably the redshift is denoted s.z as one of these. PhotoObj p refers to photographic imaging. From these data we take p.ra and p.dec.

WHERE contains all the constraints we want to apply in our data query. These constraints are all connected with a logical AND operator, meaning that we want ALL listed constraints to be fulfilled simultaneously.

So you see, I required the redshift s.z to lie between 0,0001 and 1.0 (which is about where the quasar regime starts) . Moreover, I requested a VERY good quality flag (zConf >0.95) as to the determination of z. That is advised on the Sloan site. Finally, I request only galaxies, which is best done spectroscopically, by requiring s.specClass=2.

Next there is the request of an UV magnitude u between 0 and 20, which is more or less a default option.

Finally, in the above SQL script, I requested RA to lie between 0 and 180 degrees. Actually, to avoid internal overflows and loong response times, it is most advisable to read out the data within successive RA windows of 45 degrees, covering the total range between 0 and 360 degrees. In Dec I applied NO constraints whatsoever.

Finally you select the output as a CSV output format, which means bare text. You can also choose HTML output of course for smaller data sets. Since I work on the result with Perl, text format is much better, though.

It's easy, isn't it?

The result of this little script left me with a sample of 335098 SDSS galaxies with 0<z<1 and 0 <= RA <= 360 degrees. Note that this is the finalized DR6 data! So it's worth collecting

Next I wrote a little Perl script that reads in these raw data, converts the RA values to decimal hours and calculates the comoving distance with my exact Perl subroutine, using from WMAP 2008, 5 years running.

• Omega_Lambda = 0.73, Omega_matter = 0.23, corresponding to a flat Universe.
• Omega_radiation as evaluated in terms of 3 neutrinos.
• for the Hubble constant I now took the (averaged) 5 years legacy value of H0 = 71.0 [km/sec/Mpc].
• It's exactly the same routine that is also part of my deepsky.pl Perl script in the official Celestia sources.

EDIT:
Note in the new run of today, I decided to upgrade all cosmological parameters (from WMAP 2007, 3 years running) to their latest WMAP 2008, 5 years running values. This is now consistently different since yesterday. Also the deepsky.dsc data for Celestia have been rerun with the latest Hubble constant H0=71.0.

My used parameters also agree exactly with those of this "official" cosmology online calculator (Ned Wright):

Ned Wright's Cosmology Calculator
where I have now cross checked my conversion of the redshift to distances for the Sloan data.

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Since these results may be of considerable interest to some of you, I prepared an zip archive for download:

335 098 finalized SDSS Galaxies (DR6) , with z<1, for Download (RA, DEC, Distance)

EDIT: : of course this archive is now also corrected and interested people should download it once more (SORRY!):


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The archive includes also my little Perl script and the direct raw output from Sloan. So you can play yourself as much as you like!

Next I wrote some Maple code to display and analyze these new and most interesting data in connection with Celestia's 10000+ galaxies!


Here are some most interesting plots (all corrected!):

First of all a summary "conformal Princeton" plot (RA vs log10(distance [ly]) for the 335098 Sloan DSS galaxies (red dots), just like I did it above for the Celestia data (blue dots).



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You clearly see these vertical strings of galaxies notably in the center, corresponding to the Virgo I cluster region.
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Next the 335098 Sloan galaxies (red dots) and my 10000+ Celestia galaxies (blue dots) plotted together in one "unifying" plot:

(Click for a larger Plot)




Next we look into more detail:

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Look at the amazing consistency of the red and blue galaxy dots around the conspicuous vertical steaks in the Virgo I cluster regime of RA!!
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(Click for a larger Plot)



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The next plot zooms into the proper transition region between my blue Celestia galaxies and the red Sloan galaxies. You see clearly the RICH vertical streak patters in the Sloan data as well as in the Celestia data and the mutual consistency of these patterns! NO doubt anymore: these streaks are PHYSICAL manifestations of the filiamnetary large scale structure!
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The last two plots focus on the other regions in RA, where the horizontal filiaments dominate!
both in the Sloan and the Celestia data:






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Altogether, the agreement in the filiamentary fine structure between the Celestia and Sloan galaxies is spectacular now (after correction of my STUPID normalization error).

We are now ready to do lots of interesting studies with combining these data and including a host of further properties from the Sloan database, like Hubble morphological types, magnitudes, colors etc. This will allow to prepare most interesting statistical distributions in these variables!
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Enjoy,
Fridger

Cham, how do you convert such database in cmod?

Friends,

As I explained in my PROLOG before the corrected long post of mine from yesterday, there was a STUPID conversion error that crept into the Sloan DSS distance conversion. I had to redo all the plots and decided to rather edit my above long post, than to add the same stuff once more...

So please start again reading my previous post! It's definitely worth it I think
Sorry for any inconveniences. Also please download the data archive with the extracted Sloan DSS DR6 data once more, if you are interested.

Fridger

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Well now, maybe I ain't as Brain-Dead as I thought I was...
Simply did not understand what the previous plots were displaying, but can see now with relative ease.
Thanks Guckytos! Us Brain-Dead types have to stick together here.

Also takes some real guts to advise the Good Doctor that he may have committed an error.
Thanks for the interesting explanation Herr Doctor... Your honesty is always appreciated at this end.
Great Stuff.

Bob,

...appreciated! . This stuff is FASCINATING!

Ever contemplated, how these delicate filiaments of galaxies might have arisen? Since the red and the blue dots agree so well now, we have learned by this comparative study, the we got already quite a few large scale filiaments in our Celestia data base!!

This familiar VIDEO (1024x768 divx5) reminds us spectacularly what the discussion is all about:

( VIDEO:) Flying through the Filiamentary (Millenium) Universe


Cheers,
Fridger

Just for other Brain-Dead users here...

I am finding all of this extremely interesting, and I am getting an education in the terminology and some of the
relevant issues involved with the current theories behind the development and formation of our universe.

Just in case none of this makes any sense to the less neuron-endowed reading through this topic, I managed to find
a few friendlier web sites for use in explaining some of the more complex theories and arguments going on within the
field of cosmology in general.

If you don't mind the post here Good Doctor, others may wish to view a brief explanation of these simply
fascinating theories of the universe on The Expanding Universe page.

Bob,

unfortunately, I was unable to load that link.

In general, I think it is good if non-experts suggest well-written articles for non-experts. I can hardly propose such articles, although I know VERY many reviews/papers/books about Cosmology. I can however judge the contents of anything about that matter VERY well. So my only wish would be that the writer really knows what he/she is talking about! One of my favorite scientists, world famous for some of his popular talks/books on Cosmology, is Edward ("Rocky") Kolb, the head of the Univ. Chicago astrophysics group. I have heard quite a number of such talks by him after conference dinners and the like

Fridger

Bob,

now I managed to load that site in your link. Well, I just noted that the writers are basically junior highschool kids.
They certainly don't have an in depth knowledge YET . But if you think you can understand what they write, why not. There are certainly other alternatives that are written by much more competent authors and still well understandable for the public. If I find a better choice (from my perspective!), I will let you know, of course.

Cheers,
Fridger

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To what extent has the "Finger of God" radial dispersion effect been compensated for in the galaxies' distances?

http://web.ipac.caltech.edu/staff/jarre ... /fgod.html

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Selden

Selden,

normally I don't deal with "Fingers of God" mystics but rather prefer to discuss the generic and very familiar problem of peculiar velocity components of galaxies. This is indeed a serious problem, notably for some galaxies of the local group that are part of big clusters..

Here is some parts of a shatters.net forum post of mine, where I particularly emphasized that problem to Cham in the context of his "quick" analyisis and his reproaches as to my deepsky.dsc data. You find the full post in his List of galactic clusters and voids thread at shatters on Aug 30th:



For my NGC/IC distances (Celestia) I used as much as 10 different methods, some of which are independent of peculiar velocities.

In the present analysis of as many 335 098 Sloan DR6 galaxies, there is no way to account for the peculiar velocity components. The redshift z is determined spectroscopically as you sure know. From there one can EXACTLY calculate the RADIAL co-moving distance.

But certainly at LOW z in particular, one has little choice of comparing "apples with peers" to some extent.

Fridger

Well, they certainly know more about the subject matter than I did and/or do.

Please Good Doctor, if you find anything which may of interest to the Brain-Dead out here in the real world,
I would very much appreciate any links. As you know, I am always learning from you guys. That's all part
of the fun here. I'll shut up now, and get out of the way of this thread. Sorry to have interrupted, but I really
enjoy learning about these things.

Thanks again, Bob

Well, this might be, but we cannot be sure how RELIABLE things are one can read there. WEBsites tend to be believed


Yes Bob, I promise to look around for something really sound AND pedagogical.

Fridger

Here is a nice overview talk from Oct 2007 about the current Sloan DSS and various access tools to their data servers. It is originally in PowerPoint format. I converted it to a PDF, so everyone can look at it.

Sloan_DSS DR6 Overview (Talk Oct 2007)

Let me know whether this is a useful level/presentation!

Fridger