Graph with Saul and Perlmutter's results

[Niles]

Hi guys

Please take a look at this familiar graph: http://www.iop.org/EJ/article/1538-3881/116/3/1009/980111.fg7.html

I've read about how the data got conceived and all, but I can't see why that graph indicates that $$\Omega_m=0.3$$ and $$\Omega_\Lambda=0.7$$?

 

[mathman]

This is the point where the major axis of the inner solid ellipse crosses the line representing total omega = 1.

 

[Wallace]

Is the confusion due to the fact that the ellipse is actually centered on something crazy, like (0.9,1.5) rather than the (0.3,0.7) you expected? As mathman pointed out, the key point is that (0.3,0.7) is where the ellipse crosses total omega=1.

The reason that this is important however is because of the rest of the data. The SN alone leave you with the large ellipse, but have a look at http://snap.lbl.gov/images/omlam.jpg" figure. It shows the way three important data sets, SN, the CMB and galaxy cluster constrain the parameters. As can be see, the CMB basically tells you that omega=1, but doesn't say what the breakup of that is, the SN tell you that the break up is (0.3,0.7) if omega=1 and the clusters tell you independently that omega matter =0.3.

It is the fact that these and other data sets agree independantly, i.e. the contours all cross at a point, that we call this the concordance model. This figure is from the SuperNovae Acceleration Probe (SNAP) website. This is a planned space mission to study dark energy. Note the tiny region they hope to constrain the parameters to!