lumdist: Calculate luminosity distance (in Mpc) of an object given its...
In astrolibR: Astronomy Users Library

Description Usage Arguments Details Value Author(s) References Examples

Calculate luminosity distance (in Mpc) of an object given its redshift

1	lumdist(z, h0=70, k, lambda0, omega_m, q0)

`z`	redshift, positive scalar or vector
`h0`	Hubble expansion parameter, in km/s/Mpc (default = 70.0)
`k`	curvature constant normalized to the closure density (default = 0.0 corresponding to a flat universe)
`omega_m`	matter density normalized to the closure density (default = 0.3)
`lambda0`	cosmological constant normalized to the closure density (default = 0.7)
`q0`	deceleration parameter, scalar (default = 0.55)

The luminosity distance in the Friedmann-Robertson-Walker model is taken from Carroll et al. (1992, p.511). It uses a closed form (Mattig equation) to compute the distance when the cosmological constant is zero, and otherwise computes the partial integral using the R function integrate. The integration can fail to converge at high redshift for closed universes with non-zero lambda.

No more than two of the four parameters (k, omega_M, lambda0, q0) should be specified. None of them need be specified if the default values are adopted.

lumdist

The result of the function is the luminosity distance (in Mpc) for each input value of z

Written W. Landsman Raytheon ITSS 2000

R adaptation by Arnab Chakraborty June 2013

Carroll, S. M., Press, W. H. and Turner, E. L., 1992, The cosmological constant, Ann. Rev. Astron. Astrophys., 30, 499-542

# Plot the distance of a galaxy in Mpc as a function of redshift out 
#  to z = 5.0, assuming the default cosmology (Omega_m=0.3, Lambda = 0.7,
#  H0 = 70 km/s/Mpc)

z <- seq(0,5,length=51)
plot(z, lumdist(z), type='l', lwd=2, xlab='z', ylab='Distance (Mpc)') 

# Now overplot the relation for zero cosmological constant and 
# Omega_m=0.3

lines(z,lumdist(z, lambda=0, omega_m=0.3), lty=2, lwd=2)