Class Distances

java.lang.Object
uk.ac.starlink.ttools.func.Distances

public class Distances extends Object
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, astro-ph/9905116 v4 (2000).

Since:
26 Jan 2007
Author:
Mark Taylor
  • Field Summary

    Fields
    Modifier and Type
    Field
    Description
    static final double
    Number of metres in a parsec.
    static final double
    Number of seconds in a year.
    static final double
    Speed of light in m/s.
  • Method Summary

    Modifier and Type
    Method
    Description
    static double
    angularDiameterDistance(double z, double H0, double omegaM, double omegaLambda)
    Angular diameter distance.
    static double
    comovingDistanceL(double z, double H0, double omegaM, double omegaLambda)
    Line-of-sight comoving distance.
    static double
    comovingDistanceT(double z, double H0, double omegaM, double omegaLambda)
    Transverse comoving distance.
    static double
    comovingVolume(double z, double H0, double omegaM, double omegaLambda)
    Comoving volume.
    static double
    lookbackTime(double z, double H0, double omegaM, double omegaLambda)
    Lookback time.
    static double
    luminosityDistance(double z, double H0, double omegaM, double omegaLambda)
    Luminosity distance.
    static double
    MpcToM(double distMpc)
    Converts from MegaParsecs to metres.
    static double
    mToMpc(double distM)
    Converts from metres to MegaParsecs.
    static double
    zToAge(double z)
    Quick and dirty function for converting from redshift to time.
    static double
    zToDist(double z)
    Quick and dirty function for converting from redshift to distance.

    Methods inherited from class java.lang.Object

    clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait
  • Field Details

    • SPEED_OF_LIGHT

      public static final double SPEED_OF_LIGHT
      Speed of light in m/s.
      See Also:
    • METRE_PER_PARSEC

      public static final double METRE_PER_PARSEC
      Number of metres in a parsec.
      See Also:
    • SEC_PER_YEAR

      public static final double SEC_PER_YEAR
      Number of seconds in a year.
      See Also:
  • Method Details

    • MpcToM

      public static double MpcToM(double distMpc)
      Converts from MegaParsecs to metres.
      Parameters:
      distMpc - distance in Mpc
      Returns:
      distance in m
    • mToMpc

      public static double mToMpc(double distM)
      Converts from metres to MegaParsecs.
      Parameters:
      distM - distance in m
      Returns:
      distance in Mpc
    • zToDist

      public static double zToDist(double 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.

      Parameters:
      z - redshift
      Returns:
      some distance measure in Mpc
    • zToAge

      public static double zToAge(double 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.

      Parameters:
      z - redshift
      Returns:
      'age' of photons from redshift z in Gyr
    • comovingDistanceL

      public static double comovingDistanceL(double z, double H0, double omegaM, double omegaLambda)
      Line-of-sight comoving distance.
      Parameters:
      z - redshift
      H0 - Hubble constant in km/sec/Mpc
      omegaM - density ratio of the universe
      omegaLambda - normalised cosmological constant
      Returns:
      line-of-sight comoving distance in Mpc
    • comovingDistanceT

      public static double comovingDistanceT(double z, double H0, double omegaM, double omegaLambda)
      Transverse comoving distance.
      Parameters:
      z - redshift
      H0 - Hubble constant in km/sec/Mpc
      omegaM - density ratio of the universe
      omegaLambda - normalised cosmological constant
      Returns:
      transverse comoving distance in Mpc
    • angularDiameterDistance

      public static double angularDiameterDistance(double z, double H0, double omegaM, double omegaLambda)
      Angular diameter distance.
      Parameters:
      z - redshift
      H0 - Hubble constant in km/sec/Mpc
      omegaM - density ratio of the universe
      omegaLambda - normalised cosmological constant
      Returns:
      angular diameter distance in Mpc
    • luminosityDistance

      public static double luminosityDistance(double z, double H0, double omegaM, double omegaLambda)
      Luminosity distance.
      Parameters:
      z - redshift
      H0 - Hubble constant in km/sec/Mpc
      omegaM - density ratio of the universe
      omegaLambda - normalised cosmological constant
      Returns:
      luminosity distance in Mpc
    • lookbackTime

      public static double lookbackTime(double z, double H0, double omegaM, double 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.
      Parameters:
      z - redshift
      H0 - Hubble constant in km/sec/Mpc
      omegaM - density ratio of the universe
      omegaLambda - normalised cosmological constant
      Returns:
      lookback time in Gyr
    • comovingVolume

      public static double comovingVolume(double z, double H0, double omegaM, double omegaLambda)
      Comoving volume. This returns the all-sky total comoving volume out to a given redshift z.
      Parameters:
      z - redshift
      H0 - Hubble constant in km/sec/Mpc
      omegaM - density ratio of the universe
      omegaLambda - normalised cosmological constant
      Returns:
      comoving volume in Gpc3