'Separation in transverse proper kpc corresponding to an
arcminute at redshift ``z``.
Parameters
z : array-like
Input redshifts.  Must be 1D or scalar.
Returns
d : `~astropy.units.Quantity`
The distance in proper kpc corresponding to an arcmin at each
input redshift.'

def kpc_proper_per_arcmin(self, z):

    return ((self.angular_diameter_distance(z).to(u.kpc) * arcmin_in_radians) / u.arcmin)
