w0wzCDM¶
-
class
astropy.cosmology.
w0wzCDM
(*args, **kwargs)[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
- H0
python:float
orQuantity
[‘frequency’] Hubble constant at z = 0. If a float, must be in [km/sec/Mpc]
- Om0
python:float
Omega matter: density of non-relativistic matter in units of the critical density at z=0.
- Ode0
python:float
Omega dark energy: density of dark energy in units of the critical density at z=0.
- w0
python:float
, optional Dark energy equation of state at z=0. This is pressure/density for dark energy in units where c=1.
- wz
python:float
, optional Derivative of the dark energy equation of state with respect to z. A cosmological constant has w0=-1.0 and wz=0.0.
- Tcmb0
python:float
or scalarQuantity
[‘temperature’], 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
python:float
, optional Effective number of Neutrino species. Default 3.04.
- m_nuquantity-like [‘energy’, ‘mass’] or numpy:array_like, optional
Mass of each neutrino species in [eV] (mass-energy equivalency enabled). 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
python:float
orpython: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
python:str
orpython:None
, optional Name for this cosmological object.
- H0
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
Evaluates the redshift dependence of the dark energy density.
w
(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
(z)[source]¶ Evaluates the redshift dependence of the dark energy density.
- Parameters
- znumpy:array_like
Input redshifts.
- Returns
- I
ndarray
orpython:float
The scaling of the energy density of dark energy with redshift. Returns float if input scalar.
- I
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
(z)[source]¶ Returns dark energy equation of state at redshift
z
.- Parameters
- znumpy:array_like
Input redshifts.
- Returns
- w
ndarray
orpython:float
The dark energy equation of state Returns float if input scalar.
- w
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 \(w(z) = w_0 + w_z z\).