A script to mark ALL Fridger's galaxies

[t00fri]

Here's a simple graph showing the differences between the matter dominated scenario (no cosmological constant) and the one with a CC :

distance.jpg

Martin,


I checked your above distance calculation/plot with my exact Perl routine:

For z=2, I find

• 16.59144 Gly for the exact formula which seems about OK with your plot
• 11.29172 Gly for the Lambda=0 case,
• 26.71650 Gly for the naive Hubble law result.

So you can see that for Z = O(1), the flat, matter dominated formula gives a much better agreement with the exact result than the naive Hubble law formula.

For z=0.183 I find

• 2.35033 Gly for the exact formula
• 2.15317 Gly for the Lambda=0 case,
• 2.44456 Gly for the naive Hubble law result.

So at the highest z value of my database, z= 0.183, the differences are small, indeed.

Fridger

[Cham]

Moreover, in your graph, you might also want to include the naive Hubble law distance d_Hubble = c*z/H0. Then you can appreciate how much better the first correction formula actually is...

The naive Hubble law is obvious, since it's linear and tangent to the curves above (at z = 0).

[t00fri]

Moreover, in your graph, you might also want to include the naive Hubble law distance d_Hubble = c*z/H0. Then you can appreciate how much better the first correction formula actually is...

The naive Hubble law is obvious, since it's linear and tangent to the curves above (at z = 0).

Of course it's obvious , yet it takes an evaluation of the multiplicative constant involved to see quantitatively, how long the naive Hubble law can be approximately used!

So, for example, you can see from my above numerical comparison that for small z=0.183, the naive Hubble distance is slightly closer to the exact value than the "improved" one! Would you have known this beforehand? . For larger z it's again obvious that the naive Hubble distance will become the largest, since it diverges linearly for large z...

Fridger