wCDM¶

class astropy.cosmology.wCDM(H0, Om0, Ode0, w0=-1.0, Tcmb0=2.725, Neff=3.04, m_nu=<Quantity 0.0 eV>, name=None)[source] [edit on github]¶

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

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 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 : Quantity

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. 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 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)[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 $I = \left(1 + z\right)^{3\left(1 + w_0\right)}$

efunc(z)[source] [edit on github]¶

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 consant.

Notes

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

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

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)[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 $w(z) = w_0$ .

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