# FlatwCDM¶

class astropy.cosmology.FlatwCDM(H0, Om0, 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 no spatial curvature.

This has one additional attribute beyond those of FLRW.

Parameters
H0float or Quantity

Hubble constant at z = 0. If a float, must be in [km/sec/Mpc]

Om0float

Omega matter: density of non-relativistic matter in units of the critical density at z=0.

w0float, 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.

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_nuQuantity, 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.

Examples

>>> from astropy.cosmology import FlatwCDM
>>> cosmo = FlatwCDM(H0=70, Om0=0.3, w0=-0.9)


The comoving distance in Mpc at redshift z:

>>> z = 0.5
>>> dc = cosmo.comoving_distance(z)


Methods Summary

 efunc(self, z) Function used to calculate H(z), the Hubble parameter. inv_efunc(self, z) Function used to calculate $$\frac{1}{H_z}$$.

Methods Documentation

efunc(self, z)[source]

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

Parameters
zarray-like

Input redshifts.

Returns
Endarray, 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
zarray-like

Input redshifts.

Returns
Endarray, or float if input scalar

The inverse redshift scaling of the Hubble constant.

Notes

The return value, E, is defined such that $$H_z = H_0 / E$$.