Next Previous Up Contents
Next: KCorrections
Up: General Functions
Previous: Conversions
Functions for converting between different measures of cosmological
distance.
The following parameters are used:

z: redshift

H0: Hubble constant in km/sec/Mpc
(example value ~70)

omegaM: Density ratio of the universe
(example value 0.3)

omegaLambda: Normalised cosmological constant
(example value 0.7)
For a flat universe, omegaM
+omegaLambda
=1
The terms and formulae used here are taken from the
paper by D.W.Hogg, Distance measures in cosmology,
astroph/9905116 v4
(2000).

MpcToM( distMpc )
 Converts from MegaParsecs to metres.

mToMpc( distM )
 Converts from metres to MegaParsecs.

zToDist( z )
 Quick and dirty function for converting from redshift to distance.
Warning: this makes some reasonable
assumptions about the cosmology and returns the luminosity
distance. It is only intended for approximate use. If you care
about the details, use one of the more specific functions here.

zToAge( z )
 Quick and dirty function for converting from redshift to time.
Warning: this makes some reasonable
assumptions about the cosmology. It is only intended for approximate
use. If you care about the details use one of the more specific
functions here.

comovingDistanceL( z, H0, omegaM, omegaLambda )
 Lineofsight comoving distance.

comovingDistanceT( z, H0, omegaM, omegaLambda )
 Transverse comoving distance.

angularDiameterDistance( z, H0, omegaM, omegaLambda )
 Angular diameter distance.

luminosityDistance( z, H0, omegaM, omegaLambda )
 Luminosity distance.

lookbackTime( z, H0, omegaM, omegaLambda )
 Lookback time. This returns the difference between the age of
the universe at time of observation (now) and the age of the
universe at the time when photons of redshift
z
were emitted.

comovingVolume( z, H0, omegaM, omegaLambda )
 Comoving volume. This returns the allsky total comoving
volume out to a given redshift
z
.

SPEED_OF_LIGHT
 Speed of light in m/s.

METRE_PER_PARSEC
 Number of metres in a parsec.

SEC_PER_YEAR
 Number of seconds in a year.
Next Previous Up Contents
Next: KCorrections
Up: General Functions
Previous: Conversions
TOPCAT  Tool for OPerations on Catalogues And Tables
Starlink User Note253
TOPCAT web page:
http://www.starlink.ac.uk/topcat/
Author email:
m.b.taylor@bristol.ac.uk
Mailing list:
topcatuser@jiscmail.ac.uk