CosmoMC and bias parameter

Use of Cobaya. camb, CLASS, cosmomc, compilers, etc.
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Samuel Leach
Posts: 16
Joined: October 15 2004
Affiliation: SISSA, Trieste

CosmoMC and bias parameter

Post by Samuel Leach » February 15 2005


I have a question concerning the twodf.f90 module of CosmoMC and the bias parameter.

I want to extract the value of the bias that is used in the analytic marginalisation over the matter power spectrum amplitude for a particular cosmological model. Can this be obtained directly from the analytic marginalisation formulas? I noticed that the following lines of code are commented out:

! CMB%norm(3) = sqrt(sum(th*Ninvd)/(sum1* 0.92**2) - 4./45*(CMB%omc+CMB%omb)**1.2) - &
! (CMB%omc+CMB%omb)**0.6/3
! write (*,*) CMB%norm(3)

and it gives me roughly what I'm looking for, but I don't recognise the formula here.

Thanks for your help

-Sam Leach

Sarah Bridle
Posts: 144
Joined: September 24 2004
Affiliation: University College London (UCL)

CosmoMC and bias parameter

Post by Sarah Bridle » February 16 2005

It should be possible to type in a formula that gives you the best fit bias parameter for a given model (to do it the long way you could just loop over different bias parameters and look for the peak, or can stare at the chisq equation for a bit and differentiate wrt b).

The difficulty comes in relating this number to the bias at the redshift of the survey, taking into account redshift space distortions, growth factor etc. e.g. see Lahav et al astro-ph/0112162 . Hope that helps.

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