redshift_hubble¶
-
astropy.cosmology.units.
redshift_hubble
(cosmology=None, **atzkw)[source]¶ Convert quantities between redshift and Hubble parameter and little-h.
Care should be taken to not misinterpret a relativistic, gravitational, etc redshift as a cosmological one.
- Parameters
- cosmology
Cosmology
,str
, orNone
, optional A cosmology realization or built-in cosmology’s name (e.g. ‘Planck18’). If None, will use the default cosmology (controlled by
default_cosmology
).- **atzkw
keyword arguments for
z_at_value()
- cosmology
- Returns
Equivalency
Equivalency between redshift and Hubble parameter and little-h unit.
Examples
>>> import astropy.units as u >>> import astropy.cosmology.units as cu >>> from astropy.cosmology import WMAP9
>>> z = 1100 * cu.redshift >>> equivalency = cu.redshift_hubble(WMAP9) # construct equivalency
>>> z.to(u.km / u.s / u.Mpc, equivalency) <Quantity 1565637.40154275 km / (Mpc s)>
>>> z.to(cu.littleh, equivalency) <Quantity 15656.37401543 littleh>