We present ultraviolet spectroscopy from HST/GHRS and reanalyze existing H \alpha images of the quasar/galaxy pair 3C 232/NGC 3067 and of the halo gas associated with NGC 3067 .
The spectra permit measurement of , or limits on , the column densities of \ion Fe1 , \ion Fe2 , \ion Mg1 , and \ion Mg2 in the absorbing cloud .
Two distinct models of the extragalactic radiation field are considered : ( 1 ) the ionizing spectrum is dominated by a power-law extragalactic continuum , and ( 2 ) the power-law spectrum contains a Lyman break , implying enhanced flux longward of 912 Å relative to the hydrogen-ionizing flux .
Models of the second type are required to fully explore the ionization balance of the Fe and Mg in the model cloud .
The H \alpha images constrain the escape fraction of Lyman continuum photons from the galaxy to f _ { esc } \leq 0.02 .
With the assumption that the cloud is shielded from all galactic contributions , we can constrain the intensity and shape of the extragalactic continuum .
For an AGN-dominated power-law extragalactic spectrum , we derive a limit on the extragalactic ionizing flux \Phi _ { ion } \geq 2600 photons cm ^ { -2 } s ^ { -1 } , or I _ { 0 } \geq 10 ^ { -23 } erg cm ^ { -2 } s ^ { -1 } Hz ^ { -1 } sr ^ { -1 } for a \nu ^ { -1.8 } ionizing spectrum and a cloud of constant density .
When combined with previous upper limits from the absence of H \alpha recombination emission from intergalactic clouds , our observations require 2600 \leq \Phi _ { ion } \leq 10000 photons cm ^ { -2 } s ^ { -1 } .
We show that if galactic contributions to the incident radiation are important , it is difficult to constrain \Phi _ { ion } .
These results demonstrate that galactic halo opacities and their wavelength dependence are crucial to understanding the abundance of low-ionization metals in the IGM .