A Space & astronomy forum. SpaceBanter.com

Go Back   Home » SpaceBanter.com forum » Astronomy and Astrophysics » Astronomy Misc
Site Map Home Authors List Search Today's Posts Mark Forums Read Web Partners

Hunting for new galaxy clusters



 
 
Thread Tools Display Modes
  #1  
Old December 5th 07, 01:01 PM posted to uk.sci.astronomy, sci.astro.amateur, sci.astro
ukastronomy
external usenet poster
 
Posts: 1,184
Default Hunting for new galaxy clusters

Hunting for new galaxy clusters

Counting galaxies that are within a given radius of a point just
reveals how many lie in what amounts to a volume of sky in the shape
of a cylinder. Without some method of knowing the distance to each
galaxy it is impossible to sort out genuine clusters from line of
sight arrangements of no astronomical significance.

The problems that this creates is best considered via a worked
example.

Consider galaxies identified as lying close to 233.3831d +31.1464d.
Roughly speaking this corresponds to Abell 2092 listed with a radius
of 30 arc mins and part of the Corona Borealis supercluster.

The Catalogue of Principal Galaxies lists 18 within 10 arc minutes -
21 within 12 arc minutes and the next closest at 16.7 arc minutes.
Conclusion:- galaxy cluster radius 10 to 12 arc minutes.

Hyperleda lists 28 galaxies within 10 arc minutes - 35 within 12 arc
minutes and the next closest is at 14.55 arc minutes. Conclusion:-
galaxy cluster radius 10 to 12 arc minutes

NED lists 72 and 91 galaxies respectively but there is a less clear
cut boundary if you consider the whole group. The good news is that
there is red shift data available and this is very revealing. If you
just consider galaxies with a red shift in the narrow range between
0.060 and 0.072 then 41 lies within 10 arc minutes, 45 within 12 arc
minutes with only six more if you go out to 15 arc minutes. Increasing
the red shift range to 0.057 to 0.075 only increases these numbers to
42, 46 and 52 so the chosen group is well defined. Conclusion:- galaxy
cluster radius 10 to 12 arc minutes with all members with a red shift
of between 0.060 and 0.072.

Of course red shifts do not provide an entirely reliable indication of
distance because of distortions to the local velocity field due to in-
fall onto concentrations of mass but it is a lot more to go on than
Abell et al had!

I think that this shows that there is significant scope for new galaxy
clusters to be "extracted" from already listed examples but that the
criteria for any discovery claim need to be examined and discussed.

Martin Nicholson, Daventry, England.
http://www.martin-nicholson.info/1/1a.htm

Visit the Astronomical Hall of Shame at http://www.geocities.com/queen5658/
 




Thread Tools
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

vB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Forum Jump

Similar Threads
Thread Thread Starter Forum Replies Last Post
Galaxy Clusters ??? G=EMC^2 Glazier[_1_] Misc 0 May 13th 07 03:05 PM
ASTRO: while we are posting galaxy clusters Richard Crisp[_1_] Astro Pictures 1 April 17th 07 04:32 AM
MOND falsified by titanic collision of galaxy clusters Jack Sarfatti Astronomy Misc 6 November 15th 06 10:30 PM
early morning galaxy hunting [email protected] Amateur Astronomy 3 November 18th 05 03:55 PM
Galaxy Hunting Terry A. Haimann Amateur Astronomy 3 September 4th 03 03:47 AM


All times are GMT +1. The time now is 06:19 PM.


Powered by vBulletin® Version 3.6.4
Copyright ©2000 - 2024, Jelsoft Enterprises Ltd.
Copyright ©2004-2024 SpaceBanter.com.
The comments are property of their posters.