w0wzCDM¶

class astropy.cosmology.w0wzCDM(H0, Om0, Ode0, w0=-1.0, wz=0.0, Tcmb0=2.7250000000000001, Neff=3.04, m_nu=<Quantity 0.0 eV>, name=None)[source] [edit on github]¶

Bases: astropy.cosmology.FLRW

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

The equation for the dark energy equation of state uses the simple form: $w(z) = w_0 + w_z z$ .

This form is not recommended for z > 1.

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

Dark energy equation of state at z=0. This is pressure/density for dark energy in units where c=1. A cosmological constant has w0=-1.0.

wz : float

Derivative of the dark energy equation of state with respect to z.

Tcmb0 : float or Quantity

Temperature of the CMB z=0. If a float, must be in [K]. Default: 2.725.

Neff : float

Effective number of Neutrino species. Default 3.04.

m_nu : float or ndarray or Quantity

Mass of each neutrino species, in eV. If this is a float or scalar Quantity, then all neutrino species are assumed to have that mass. If a ndarray or array Quantity, then these are the values of 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. Usually this means you must provide three neutrino masses unless you are considering something like a sterile neutrino.

name : str

Optional name for this cosmological object.

Examples

>>> from astropy.cosmology import w0wzCDM
>>> cosmo = w0wzCDM(H0=70, Om0=0.3, Ode0=0.7, w0=-0.9, wz=0.2)

The comoving distance in Mpc at redshift z:

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

Attributes Summary

`w0`	Dark energy equation of state at z=0
`wz`	Derivative of the dark energy equation of state w.r.t.

Methods Summary

`de_density_scale`(z)	Evaluates the redshift dependence of the dark energy density.
`w`(z)	Returns dark energy equation of state at redshift `z`.

Attributes Documentation

w0¶: Dark energy equation of state at z=0

wz¶: Derivative of the dark energy equation of state w.r.t. z

Methods Documentation

de_density_scale(z)[source] [edit on github]¶

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

$I = \left(1 + z\right)^{3 \left(1 + w_0 - w_z\right)} \exp \left(-3 w_z z\right)$

w(z)[source] [edit on github]¶

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 given by $w(z) = w_0 + w_z z$ .

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w0wzCDM¶

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