wpwaCDM¶

class
astropy.cosmology.
wpwaCDM
(H0, Om0, Ode0, wp=1.0, wa=0.0, zp=0, Tcmb0=0, Neff=3.04, m_nu=<Quantity 0. eV>, Ob0=None, name=None)[source] [edit on github]¶ Bases:
astropy.cosmology.FLRW
FLRW cosmology with a CPL dark energy equation of state, a pivot redshift, and curvature.
The equation for the dark energy equation of state uses the CPL form as described in Chevallier & Polarski Int. J. Mod. Phys. D10, 213 (2001) and Linder PRL 90, 91301 (2003), but modified to have a pivot redshift as in the findings of the Dark Energy Task Force (Albrecht et al. arXiv:0901.0721 (2009)): \(w(a) = w_p + w_a (a_p  a) = w_p + w_a( 1/(1+zp)  1/(1+z) )\).
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 nonrelativistic 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.
 wp : float, optional
Dark energy equation of state at the pivot redshift zp. This is pressure/density for dark energy in units where c=1.
 wa : float, optional
Negative derivative of the dark energy equation of state with respect to the scale factor. A cosmological constant has wp=1.0 and wa=0.0.
 zp : float, optional
Pivot redshift – the redshift where w(z) = wp
 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 wpwaCDM >>> cosmo = wpwaCDM(H0=70, Om0=0.3, Ode0=0.7, wp=0.9, wa=0.2, zp=0.4)
The comoving distance in Mpc at redshift z:
>>> z = 0.5 >>> dc = cosmo.comoving_distance(z)
Attributes Summary
wa
Negative derivative of dark energy equation of state w.r.t. wp
Dark energy equation of state at the pivot redshift zp zp
The pivot redshift, where w(z) = wp 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

wa
¶ Negative derivative of dark energy equation of state w.r.t. a

wp
¶ Dark energy equation of state at the pivot redshift zp

zp
¶ The pivot redshift, where w(z) = wp
Methods Documentation

de_density_scale
(z)[source] [edit on github]¶ Evaluates the redshift dependence of the dark energy density.
Parameters:  z : arraylike
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
\[ \begin{align}\begin{aligned}a_p = \frac{1}{1 + z_p}\\I = \left(1 + z\right)^{3 \left(1 + w_p + a_p w_a\right)} \exp \left(3 w_a \frac{z}{1+z}\right)\end{aligned}\end{align} \]

w
(z)[source] [edit on github]¶ Returns dark energy equation of state at redshift
z
.Parameters:  z : arraylike
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 \(w(z) = w_p + w_a (a_p  a)\) where \(a = 1/1+z\) and \(a_p = 1 / 1 + z_p\).
 H0 : float or