## GNU Astronomy Utilities

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#### 11.3.30 Cosmology library (cosmology.h)

This library does the main cosmological calculations that are commonly necessary in extra-galactic astronomical studies. The main variable in this context is the redshift ($$z$$). The cosmological input parameters in the functions below are H0, o_lambda_0, o_matter_0, o_radiation_0 which respectively represent the current (at redshift 0) expansion rate (Hubble constant in units of km/sec/Mpc), cosmological constant ($$\Lambda$$), matter and radiation densities.

All these functions are declared in gnuastro/cosmology.h. For a more extended introduction/discussion of the cosmological parameters, please see CosmicCalculator.

Function:
double
gal_cosmology_age (double z, double H0, double o_lambda_0, double o_matter_0, double o_radiation_0)

Returns the age of the universe at redshift z in units of Giga years.

Function:
double
gal_cosmology_proper_distance (double z, double H0, double o_lambda_0, double o_matter_0, double o_radiation_0)

Returns the proper distance to an object at redshift z in units of Mega parsecs.

Function:
double
gal_cosmology_comoving_volume (double z, double H0, double o_lambda_0, double o_matter_0, double o_radiation_0)

Returns the comoving volume over 4pi stradian to z in units of Mega parsecs cube.

Function:
double
gal_cosmology_critical_density (double z, double H0, double o_lambda_0, double o_matter_0, double o_radiation_0)

Returns the critical density at redshift z in units of $$g/cm^3$$.

Function:
double
gal_cosmology_angular_distance (double z, double H0, double o_lambda_0, double o_matter_0, double o_radiation_0)

Return the angular diameter distance to an object at redshift z in units of Mega parsecs.

Function:
double
gal_cosmology_luminosity_distance (double z, double H0, double o_lambda_0, double o_matter_0, double o_radiation_0)

Return the luminosity diameter distance to an object at redshift z in units of Mega parsecs.

Function:
double
gal_cosmology_distance_modulus (double z, double H0, double o_lambda_0, double o_matter_0, double o_radiation_0)

Return the distance modulus at redshift z (with no units).

Function:
double
gal_cosmology_to_absolute_mag (double z, double H0, double o_lambda_0, double o_matter_0, double o_radiation_0)

Return the conversion from apparent to absolute magnitude for an object at redshift z. This value has to be added to the apparent magnitude to give the absolute magnitude of an object at redshift z.

Function:
double
gal_cosmology_velocity_from_z (double z)

Return the velocity (in km/s) corresponding to the given redshift (z).

Function:
double
gal_cosmology_z_from_velocity (double v)

Return the redshift corresponding to the given velocity (v in km/s).

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