code: def masses_of_galaxies_within_ellipses_in_units(self, major_axis : dim.Length, unit_mass='angular',
                                                      critical_surface_density=None):
          
          return list(map(lambda galaxy: galaxy.mass_within_ellipse_in_units(
                          major_axis=major_axis, unit_mass=unit_mass, kpc_per_arcsec=self.kpc_per_arcsec,
                          critical_surface_density=critical_surface_density),
                          self.galaxies))
docs: Compute the total mass of all galaxies in this plane within a ellipse of specified major-axis.
  
          See *galaxy.angular_mass_within_ellipse* and *mass_profiles.angular_mass_within_ellipse* for details \
          of how this is performed.
  
          Parameters
          ----------
          major_axis : float
              The major-axis radius of the ellipse.
          units_luminosity : str
              The units the luminosity is returned in (eps | counts).
          exposure_time : float
              The exposure time of the observation, which converts luminosity from electrons per second units to counts.