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Institut für Astronomie und Astrophysik

Abteilung Astronomie

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LUMDIST Source code in lumdist.pro

LUMDIST

Name
    LUMDIST
Purpose
    Calculate luminosity distance (in Mpc) of an object given its redshift
Explanation
    The luminosity distance in the Friedmann-Robertson-Walker model is
    taken from  Caroll, Press, and Turner (1992, ARAA, 30, 499), p. 511
    Uses a closed form (Mattig equation) to compute the distance when the
    cosmological constant is zero.   Otherwise integrates the function using
    QSIMP.
Calling Sequence
    result = lumdist(z, [H0 = , k = , Omega_M =, Lambda0 = , q0 = ,/SILENT])
Input Parameters
    z = redshift, positive scalar or vector
Keyword Parameters
    /SILENT - If set, the program will not display adopted cosmological
        parameters at the terminal.
    H0: Hubble parameter  in km/s/Mpc, default is 70
        No more than two of the following four parameters should be
        specified.   None of them need be specified -- the adopted defaults
        are given.
    k - curvature constant, normalized to the closure density.   Default is
        0, indicating a flat universe
    Omega_m -  Matter density, normalized to the closure density, default
        is 0.3.   Must be non-negative
    Lambda0 - Cosmological constant, normalized to the closure density,
        default is 0.7
    q0 - Deceleration parameter, numeric scalar = -R*(R'')/(R')^2, default
        is -0.5
Output Parameters
    The result of the function is the luminosity distance (in Mpc) for each
    input value of z.
Example
    (1) 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)
        IDL> z = findgen(50)/10.
        IDL> plot,z,lumdist(z),xtit='z',ytit='Distance (Mpc)'
        Now overplot the relation for zero cosmological constant and
        Omega_m=0.3
        IDL> oplot,z,lumdist(z,lambda=0,omega=0.3),linestyle=1
Comments
    (1) Integrates using the IDL Astronomy Version procedure QSIMP.    (The
    intrinsic IDL QSIMP function is not called because of its ridiculous
    restriction that only scalar arguments can be passed to the integrating
    function.)
    (2) Can fail to converge at high redshift for closed universes with
    non-zero lambda.   This can presumably be fixed by replacing QSIMP with
    an integrator that can handle a singularity
Procedures Used
    COSMO_PARAM, QSIMP
Revision History
    Written   W. Landsman        Raytheon ITSS       April 2000
    Avoid integer overflow for more than 32767 redshifts  July 2001

Last modified by pro2html on 2001 August 07 at 09:31 UTC

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Jörn Wilms (wilms@astro.uni-tuebingen.de)
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