zang {astrolibR} R Documentation

## 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)

### 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`

.

### Value

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

### Author(s)

Written J. Hill STX 1988

R adaptation by Arnab Chakraborty June 2013

`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)')
```

[Package astrolibR version 0.1 Index]