wCDM

class astropy.cosmology.wCDM(H0, Om0, Ode0, w0=-1.0, Tcmb0=0, Neff=3.04, m_nu=<Quantity 0. eV>, Ob0=None, name=None)

Bases: astropy.cosmology.FLRW

FLRW cosmology with a constant dark energy equation of state and curvature.

This has one additional attribute beyond those of FLRW.

Parameters:

H0 : float or Quantity

Hubble constant at z = 0. If a float, must be in [km/sec/Mpc]

Om0 : float

Omega matter: density of non-relativistic matter in units of the critical density at z=0.

Ode0 : float

Omega dark energy: density of dark energy in units of the critical density at z=0.

w0 : float, optional

Dark energy equation of state at all redshifts. This is pressure/density for dark energy in units where c=1. A cosmological constant has w0=-1.0.

Tcmb0 : float or scalar Quantity, optional

Temperature of the CMB z=0. If a float, must be in [K]. Default: 0 [K]. Setting this to zero will turn off both photons and neutrinos (even massive ones).

Neff : float, optional

Effective number of Neutrino species. Default 3.04.

m_nu : Quantity, optional

Mass of each neutrino species. If this is a scalar Quantity, then all neutrino species are assumed to have that mass. Otherwise, the mass of each species. The actual number of neutrino species (and hence the number of elements of m_nu if it is not scalar) must be the floor of Neff. Typically this means you should provide three neutrino masses unless you are considering something like a sterile neutrino.

Ob0 : float or None, optional

Omega baryons: density of baryonic matter in units of the critical density at z=0. If this is set to None (the default), any computation that requires its value will raise an exception.

name : str, optional

Name for this cosmological object.

Examples

>>> from astropy.cosmology import wCDM
>>> cosmo = wCDM(H0=70, Om0=0.3, Ode0=0.7, w0=-0.9)

The comoving distance in Mpc at redshift z:

>>> z = 0.5
>>> dc = cosmo.comoving_distance(z)

Attributes Summary

w0	Dark energy equation of state

Methods Summary

de_density_scale(z)	Evaluates the redshift dependence of the dark energy density.
efunc(z)	Function used to calculate H(z), the Hubble parameter.
inv_efunc(z)	Function used to calculate \(\frac{1}{H_z}\).
w(z)	Returns dark energy equation of state at redshift z.

Attributes Documentation

w0

Dark energy equation of state

Methods Documentation

de_density_scale(z)

Evaluates the redshift dependence of the dark energy density.

Parameters:

z : array-like

Input redshifts.

Returns:

I : ndarray, or float if input scalar

The scaling of the energy density of dark energy with redshift.

Notes

The scaling factor, I, is defined by \(\rho(z) = \rho_0 I\), and in this case is given by \(I = \left(1 + z\right)^{3\left(1 + w_0\right)}\)

efunc(z)

Function used to calculate H(z), the Hubble parameter.

Parameters:

z : array-like

Input redshifts.

Returns:

E : ndarray, or float if input scalar

The redshift scaling of the Hubble constant.

Notes

The return value, E, is defined such that \(H(z) = H_0 E\).

inv_efunc(z)

Function used to calculate \(\frac{1}{H_z}\).

Parameters:

z : array-like

Input redshifts.

Returns:

E : ndarray, or float if input scalar

The inverse redshift scaling of the Hubble constant.

Notes

The return value, E, is defined such that \(H_z = H_0 / E\).

w(z)

Returns dark energy equation of state at redshift z.

Parameters:

z : array-like

Input redshifts.

Returns:

w : ndarray, or float if input scalar

The dark energy equation of state

Notes

The dark energy equation of state is defined as \(w(z) = P(z)/\rho(z)\), where \(P(z)\) is the pressure at redshift z and \(\rho(z)\) is the density at redshift z, both in units where c=1. Here this is \(w(z) = w_0\).