idlastro / Astronomical Utilities: ZANG

[Source code]

NAME
ZANG
PURPOSE
Determine the angular size of an object as a function of redshift
EXPLANATION
Requires an input size in kpc and returns an angular size in arc seconds
Default cosmology has a Hubble constant of 70 km/s/Mpc, Omega (matter)
=0.3 and a normalized cosmological constant Lambda = 0.7; however these
values can be changed with appropriate keywords.
CALLING SEQUENCE
angsiz = zang( dl, [ z, H0 =, Omega_m =, Lambda0 = , q0 = , k =, 
                        /SILENT] )
INPUTS
dl - linear size of the object *in kpc*, non-negative scalar or vector
z - redshift of object, postive  scalar or vector
    Either dl and z must have the same number of elements, or at least
    one of them must be a vector.
OPTIONAL INPUT KEYWORDS
H0 -  Hubble constant 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, default values 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 -0.55
Note that Omega_m + lambda0 + k = 1 and q0 = 0.5*omega_m - lambda0
OUTPUT
angsiz - Angular size of the object at the given redshift in 
        arc seconds 
EXAMPLE
(1) What would be the angular size of galaxy of diameter 50 kpc at a redshift
    of 1.5 in an open universe with Lambda = 0 and Omega (matter) = 0.3.
    Assume the default Hubble constant value of 70 km/s/Mpc.
    IDL> print,zang(50,1.5, Lambda = 0,omega_m = 0.3)
           ====> 6.58 arc seconds
(2) Now plot the angular size of a 50 kpc diameter galaxy as a function of 
    redshift for the default cosmology (Lambda = 0.7, Omega_m=0.3) up to 
    z = 0.5
    IDL> z = findgen(50)/10. + 0.1    ;Angular size undefined at z = 0
    IDL> plot,z,zang(50,z),xtit='z',ytit='Angular Size (")'
NOTES
This procedure underwent a major revision in April 2000 to allow for a 
cosmological constant, ***including a change of the calling sequence***
Be sure to supply the input linear size dl in units of kpc.
PROCEDURES CALLED
LUMDIST() -- Calculates the luminosity distance
REVISION HISTORY
Written    J. Hill   STX           July, 1988
Converted to IDL V5.0   W. Landsman   September 1997
Major rewrite to call LUMDIST function  W. Landsman   April 2000