Redshift Unit

[nstarman]

Description

It's a dimensionless unit that useful for redshift-related equivalencies, like redshift-dimensionless, and cosmology-dependent conversions like redshift-temperature, redshift-distance.
From discussion with @mhvk and @adrn.

Would also be useful for cosmology calculations to return instead of a float.

[pllim]

We already have https://docs.astropy.org/en/latest/api/astropy.modeling.functional_models.RedshiftScaleFactor.html#astropy.modeling.functional_models.RedshiftScaleFactor .

[adrn]

@pllim ?? Unless I do'nt understand RedshiftScaleFactor, I think the context is very different! We're talking about a new dimensionless unit meant to mark that a quantity is a special kind of dimensionless (i.e. a redshift), not a new class or functional form to compute a scale factor from a redshift.

[pllim]

Hmm, ok. But how will it work with our redshift model?