astrolibR (version 0.1)

zang: Determine the angular size of an object as a function of redshift

Description

Determine the angular size of an object as a function of redshift

Usage

zang(dl, z, h0, k, lambda0, omega_m, q0)

Arguments

dl

linear size of the object, in kpc, scalar or vector

z

redshift, 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)

lambda0

cosmological constant normalized to the closure density (default = 0.7)

omega_m

matter density normalized to the closure density (default = 0.3)

q0

deceleration parameter, scalar corresponding to

-R*(R'')/(R')^2

(default = -0.55)

Value

angsiz

angular size of the object at the given redshift, in arc seconds, scalar or vector

Details

This function 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 by the user. Note that

Omega_m + lambda0 + k = 1

and

q0 = 0.5*omega_m - lambda0

.

See Also

lumdist

Examples

# 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.
# Result: 6.58 arc seconds
      
zang(50, 1.5, lambda = 0, omega_m = 0.3)

# 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

# zseq = seq(0.01,0.5,length=50)
# plot(zseq, zang(50.0,zseq),xlab='z',ylab='Angular Size (arcsec)')