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- Astropy v5.2.1 »
- Cosmological Calculations (`astropy.cosmology`) »
- Cosmological Units and Equivalencies »
- with_redshift

# with_redshift

astropy.cosmology.units.with_redshift(cosmology=None, *, distance='comoving', hubble=True, Tcmb=True, atzkw=None)

  Convert quantities between measures of cosmological distance.

  Note: by default all equivalencies are on and must be explicitly turned off. 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`).

    distance{‘comoving’, ‘lookback’, ‘luminosity’} or `python:None` (optional, keyword-only)

      The type of distance equivalency to create or `None`. Default is ‘comoving’.

    hubble bool (optional, keyword-only)

      Whether to create a Hubble parameter <-> redshift equivalency, using `Cosmology.H`. Default is `True`.

    Tcmb bool (optional, keyword-only)

      Whether to create a CMB temperature <-> redshift equivalency, using `Cosmology.Tcmb`. Default is `True`.

    atzkw `python:dict` or `python:None` (optional, keyword-only)

      keyword arguments for `z_at_value()`

  Returns:
    `Equivalency`

      With equivalencies between redshift and distance / Hubble / temperature.

  Examples

      >>> import astropy.units as u
      >>> import astropy.cosmology.units as cu
      >>> from astropy.cosmology import WMAP9

      >>> equivalency = cu.with_redshift(WMAP9)
      >>> z = 1100 * cu.redshift

  Redshift to (comoving) distance:

      >>> z.to(u.Mpc, equivalency)
      <Quantity 14004.03157418 Mpc>

  Redshift to the Hubble parameter:

      >>> z.to(u.km / u.s / u.Mpc, equivalency)
      <Quantity 1565637.40154275 km / (Mpc s)>

      >>> z.to(cu.littleh, equivalency)
      <Quantity 15656.37401543 littleh>

  Redshift to CMB temperature:

      >>> z.to(u.K, equivalency)
      <Quantity 3000.225 K>