Cosmology computations

Code author: Wilfried Mercier - IRAP <wilfried.mercier@irap.omp.eu>

A set of functions to easily compute standard calculations in extragalactic physics using cosmology.

Note

This relies heavily on a custom, Python 3 adapted version of cosmolopy.

galaxy.cosmology.COSMOLOGY = {'h': 0.72, 'omega_M_0': 0.3, 'omega_k_0': 0.0, 'omega_lambda_0': 0.7}

Default cosmology

galaxy.cosmology.angular_diameter_size(z: Union[int, float], theta: Union[int, float], scaleFactor: Union[int, float] = 1.0, cosmology: Optional[Dict] = None) → float[source]

Code author: Wilfried Mercier - IRAP <wilfried.mercier@irap.omp.eu>

Compute the size of an object with extent theta at redshift z from the angular diameter distance.

Parameters

  • z (int or float) – redshift of the object

  • theta (int or float) – angle subtended by the object. Unit should be in radians. If not, provide a scaling factor with scaleFactor.

  • cosmology (dict) –

    (Optional) parameters for the desired cosmology. See cosmolopy for more information.

  • scaleFactor (int or float) –

    (Optional) if theta is not in radian, please provide a correct scale factor following the formula

    \[\theta [{\rm{rad}}] = \theta [{\rm{your~unit}}] \times scaleFactor [{\rm{rad/your~unit}}].\]

Returns

physical size in kpc

Return type

float

galaxy.cosmology.comoving_los(z1: Union[int, float], z2: Union[int, float], cosmology: Optional[Dict] = None) → float[source]

Code author: Wilfried Mercier - IRAP <wilfried.mercier@irap.omp.eu>

Compute the line of sight comoving distance between objects.

Parameters

  • z1 (int or float) – redshift of the 1st object

  • z2 (int or float) – redshift of the 2nd object

  • cosmology (dict) –

    (Optional) parameters for the desired cosmology. See cosmolopy for more information.

Returns

comoving distance in Mpc

Return type

float

galaxy.cosmology.comoving_separation(z: Union[int, float], theta: Union[int, float], cosmology: Optional[Dict] = None) → float[source]

Code author: Wilfried Mercier - IRAP <wilfried.mercier@irap.omp.eu>

Compute the tranverse distance (at fixed redshift) between objects separated by an angle theta on the sky in comoving units.

Parameters

  • z (int or float) – redshift of the object

  • theta (int or float) – angle subtended by the object. Unit should be in radians. If not, provide a scaling factor with scaleFactor.

  • cosmology (dict) –

    (Optional) parameters for the desired cosmology. See cosmolopy for more information.

Returns

comoving separation in Mpc

Return type

float

galaxy.cosmology.dz_from_dage(z: Union[int, float], dage: Union[int, float], cosmology: Optional[Dict] = None) → Tuple[float, float][source]

Code author: Wilfried Mercier - IRAP <wilfried.mercier@irap.omp.eu>

Compute the redshift upper and lower bounds around a given redshift such that they are dage Gyr apart from the reference redshift.

Parameters

  • z (int or float) – reference redshift

  • dage (int or float) – age interval in Gyr

  • cosmology (dict) –

    (Optional) parameters for the desired cosmology. See cosmolopy for more information.

Returns

upper and lower redshift bounds

Return type

float, float

galaxy.cosmology.separation(z: Union[int, float], ra1: float, dec1: float, ra2: float, dec2: float, units: Union[str, List[str]] = ['deg', 'deg', 'deg', 'deg']) → float[source]

Code author: Wilfried Mercier - IRAP <wilfried.mercier@irap.omp.eu>

Compute the comoving separation between two objects at the same redshift given their position.

Parameters

  • z (int or float) – redshift of the two objects

  • ra1 (float) – right ascension of the first object

  • dec1 (float) – declination of the first object

  • ra2 (float) – right ascension of the second object

  • dec2 (float) – declination of the second object

  • units (list[float] or list[astropy unit] or str) – units of the different coordinates in this order: ra1, dec1, ra2, dec2

Returns

comoving separation in Mpc

Return type

float

Raises

ValueError – if units is neither an iterable of length 4 or a str