uk.ac.starlink.ttools.func
Class Distances

java.lang.Object
  extended by 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:

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
static double METRE_PER_PARSEC
          Number of metres in a parsec.
static double SEC_PER_YEAR
          Number of seconds in a year.
static double SPEED_OF_LIGHT
          Speed of light in m/s.
 
Method Summary
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 Detail

SPEED_OF_LIGHT

public static final double SPEED_OF_LIGHT
Speed of light in m/s.

See Also:
Constant Field Values

METRE_PER_PARSEC

public static final double METRE_PER_PARSEC
Number of metres in a parsec.

See Also:
Constant Field Values

SEC_PER_YEAR

public static final double SEC_PER_YEAR
Number of seconds in a year.

See Also:
Constant Field Values
Method Detail

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


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