w0wzCDM¶

class
astropy.cosmology.
w0wzCDM
(H0, Om0, Ode0, w0=1.0, wz=0.0, Tcmb0=0, Neff=3.04, m_nu=<Quantity 0. eV>, Ob0=None, name=None)[source]¶ 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
 H0float or
Quantity
Hubble constant at z = 0. If a float, must be in [km/sec/Mpc]
 Om0float
Omega matter: density of nonrelativistic matter in units of the critical density at z=0.
 Ode0float
Omega dark energy: density of dark energy in units of the critical density at z=0.
 w0float, optional
Dark energy equation of state at z=0. This is pressure/density for dark energy in units where c=1.
 wzfloat, optional
Derivative of the dark energy equation of state with respect to z. A cosmological constant has w0=1.0 and wz=0.0.
 Tcmb0float 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).
 Nefffloat, 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.
 Ob0float 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.
 namestr, optional
Name for this cosmological object.
 H0float or
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
Dark energy equation of state at z=0
Derivative of the dark energy equation of state w.r.t.
Methods Summary
de_density_scale
(self, z)Evaluates the redshift dependence of the dark energy density.
w
(self, 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
(self, z)[source]¶ Evaluates the redshift dependence of the dark energy density.
 Parameters
 zarray_like
Input redshifts.
 Returns
 Indarray, 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
(self, z)[source]¶ Returns dark energy equation of state at redshift
z
. Parameters
 zarray_like
Input redshifts.
 Returns
 wndarray, 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 \(w(z) = w_0 + w_z z\).