cosdist: Cosmological distance calculator

In asgr/simpack: Functions for calculating orbits and interacting with the Gadget N-body code

Description

This function allows comoving, angular size and luminosity distances to be calculated for a given redshift, it can also return look back time. It makes use of curvature properly using the relation OmegaM+OmegaL+OmegaK=1, but by default it assumes a flat Universe where only OmegaM needs to be specified.

Usage

cosdist(z = 0, H0 = 100, OmegaM = 0.3, OmegaL = 1 - OmegaM, age = FALSE)

Arguments

z	Redshift (can be a vector)
H0	Hubble constant (default is H0=100 (km/s)/Mpc)
OmegaM	Omega matter (default is 0.3)
OmegaL	Omega Lambda (default is for a flat Universe with OmegaL=1-OmegaM)
age	Flag to tell program to return age or not- this slows calculation, so is by default turned off

Details

Function is based on D. W. Hogg et all 1999 (arXiv 9905116)

Value

Function returns a data.frame (even if only 1 redshift if requested) with the following columns:

z	Requested redshift
CoDist	Line-of-sight (i.e. radial) comoving distance in units of Mpc
LumDist	Luminosity distance in units of Mpc
AngDist	Angular size distance in units of Mpc
CoDistTran	Transverse comoving distance in units of Mpc
DistMod	The distance modulus used where AbsMag = ApMag - DistMod, and DistMod = 5log10(LumDist)+25
AngArcSec	Physical projected size of an arcsec at z in units of kpc/arcsec
CoVolGpc3	Comoving volume of Universe within z in units of Gpc^3

If age=TRUE is set then three extra pieces of age information are calculated for each z as extra columns:

HubTime	Approximate Hubble age of the Universe in units of years
UniAgeNow	Age of the Universe now in units of years
UniAgeAtz	Age of the Universe at the specified redshift (z) in units of years
TravelTime	Light travel time from the specified redshift (AKA look back time) in units of years

Author(s)

Aaron Robotham

References

Based on the equations in Hogg D.W., 1999, arXiv, 9905116 and Wright E.L., 2006, PASP, 118, 1711

See Also

snapwrite,snapread,genhalo,addhead,virialfuncs

Examples

print(cosdist(0.3,70))

redshifts=seq(0,3,by=0.01)

plot(redshifts,cosdist(redshifts,70)[,'CoDist'],type='l',col='darkgreen',xlab='Redshift / z',ylab='Distance / Mpc')
lines(redshifts,cosdist(redshifts,70)[,'LumDist'],col='red')
lines(redshifts,cosdist(redshifts,70)[,'AngDist'],col='blue')
legend('topleft',legend=c('Comoving Distance','Luminosity Distance','Angular Size Distance'),col=c('darkgreen','red','blue'),lty=1)

plot(redshifts,cosdist(redshifts,70,age=TRUE)[,'TravelTime'],type='l',xlab='Redshift / z',ylab='Light travel time / Yrs')

asgr/simpack documentation built on May 12, 2019, 4:40 a.m.