Double x-axis in one plot

[Fil8]

Output spectra should have a double x-axis:

• frequency in GHz
• velocity (cz)

and an option to plot a vertical line at the redshift/expected HI frequency of the galaxy.

[Fil8]

Try with some variation of this code (by H. Stacey)

from matplotlib import pyplot as plt
from matplotlib import transforms as mtransforms
from mpl_toolkits.axes_grid.parasite_axes import SubplotHost


class Wavelength2FreqTransform(mtransforms.Transform):
        input_dims = 1
        output_dims = 1
        is_separable = False
        has_inverse = True

        def __init__(self):
            mtransforms.Transform.__init__(self)

        def transform_non_affine(self, wl):
            return ((wl*un.um).to(un.GHz, equivalencies=un.spectral()).value)/(1+z)

        def inverted(self):
            return Freq2WavelengthTransform()

   class Freq2WavelengthTransform(Wavelength2FreqTransform):
        input_dims = 1
        output_dims = 1
        is_separable = False
        has_inverse = True

        def __init__(self):
            mtransforms.Transform.__init__(self)

        def transform_non_affine(self, fr):
            return ((fr*un.GHz).to(un.um, equivalencies=un.spectral()).value)

        def inverted(self):
            return Wavelength2FreqTransform()

    aux_trans = mtransforms.BlendedGenericTransform(Wavelength2FreqTransform(), mtransforms.IdentityTransform())
    fig = plt.figure(figsize=(8,6))
    ax_um = SubplotHost(fig, 1,1,1)
    fig.add_subplot(ax_um)
    ax_um.set_xlabel(r'Rest wav ($\mu$m)')

   ax_GHz = ax_um.twin(aux_trans)
   ax_GHz.set_xlabel('Observed freq (GHz)')
   ax_GHz.set_viewlim_mode('transform')
   ax_GHz.axis['right'].toggle(ticklabels=False)

   ax_GHz.set_xscale('log')
   ax_GHz.set_yscale('log')