wpwaCDM¶

class astropy.cosmology.core.wpwaCDM(H0, Om0, Ode0, wp=-1.0, wa=0.0, zp=0, Tcmb0=2.725, Neff=3.04, name='wpwaCDM') [edit on github][source]¶

Bases: astropy.cosmology.core.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)): $w(a) = w_p + w_a (a_p - a) = w_p + w_a( 1/(1+zp) - 1/(1+z) )$ .

Examples

>>> from astro.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:

>>> 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

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

Attributes Documentation

wa[source]¶: Negative derivative of dark energy equation of state w.r.t. a

wp[source]¶: Dark energy equation of state at the pivot redshift zp

zp[source]¶: The pivot redshift, where w(z) = wp

Methods Documentation

w(z) [edit on github][source]¶

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 $w(z) = w_p + w_a (a_p - a)$ where $a = 1/1+z$ and $a_p = 1 / 1 + z_p$ .