# 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)[source]

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

Attributes Documentation

w0

Dark energy equation of state

Methods Documentation

de_density_scale(self, z)[source]

Evaluates the redshift dependence of the dark energy density.

Parameters: z : array-like Input redshifts. 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(self, z)[source]

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

Parameters: z : array-like Input redshifts. 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(self, z)[source]

Function used to calculate $$\frac{1}{H_z}$$.

Parameters: z : array-like Input redshifts. 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(self, z)[source]

Returns dark energy equation of state at redshift z.

Parameters: z : array-like Input redshifts. 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 $$w(z) = w_0$$.