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# redshift_hubble

astropy.cosmology.units.redshift_hubble(cosmology=None, **atzkw)

  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`, `python:str`, or `python:None`, 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()`

  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>