astrolibR (version 0.1)

cosmo_param: Derive full set of cosmological density parameters from a partial set

Description

Derive full set of cosmological density parameters from a partial set

Usage

cosmo_param(omega_m, omega_lambda, omega_k, q0)

Arguments

omega_m

normalized matter energy density, non-negative scalar

omega_lambda

normalized cosmological constant, scalar

omega_k

normalized curvature parameter, scalar (= 0 for a flat universe

q0

deceleration parameter, scalar (= -R*(R'')/(R')^2 = 0.5*omega_m - omega_lambda)

Value

omega_m

normalized matter energy density, non-negative scalar

omega_lambda

normalized cosmological constant, scalar

omega_k

normalized curvature parameter, scalar (= 0 for a flat universe

q0

deceleration parameter, scalar (= -R*(R'')/(R')^2 = 0.5*omega_m - omega_lambda)

Details

This procedure is called by lumdist and galage to allow the user a choice in defining any two of four cosmological density parameters.

Given any two of the four input parameters -- (1) the normalized matter density omega_m (2) the normalized cosmological constant, omega_lambda (3) the normalized curvature term, Omega_k and (4) the deceleration parameter q0 -- this program will derive the remaining two. Here "normalized" means divided by the closure density so that omega_m + omega_lambda + omega_k = 1. For a more precise definition see Carroll et al (1992).

If fewer than two parameters are defined, this procedure sets default values of omega_k=0 (flat space), omega_lambda = 0.7, omega_m = 0.3 and q0 = -0.55 If more than two parameters are defined upon input (overspecification), then the first two defined parameters in the ordered list omega_m, omega_lambda, omega_k, q0 are used to define the cosmology.

References

Carroll, S. M., Press, W. H. & Turner, E. L., The cosmological constant, Ann. Rev. Astro. Astrophys, 30, 499, 1992. http://www.annualreviews.org/doi/pdf/10.1146/annurev.aa.30.090192.002435

Examples

cosmo_param(0.3, NULL, 1.0, NULL)  # returns omega_lambda=0.7 and q0=-1.05