The shape of the spectral energy distribution of active galaxies in the EUV–soft X-ray band ( 13.6 eV to 1 keV ) is uncertain because obscuration by dust and gas can hamper our view of the continuum .
To investigate the shape of the spectral energy distribution in this energy band , we have generated a set of photoionization models which reproduce the small dispersion found in correlations between high-ionization mid-infrared emission lines in a sample of hard X-ray selected AGN .
Our calculations show that a broken power-law continuum model is sufficient to reproduce the [ Ne V ] _ { 14.32 \micron } / [ Ne III ] , [ Ne V ] _ { 24.32 \micron } / [ O IV ] _ { 25.89 \micron } and [ O IV ] _ { 25.89 \micron } / [ Ne III ] ratios , and does not require the addition of a “ big bump ” EUV model component .
We constrain the EUV–soft X-ray slope , \alpha _ { i } , to be between 1.5 – 2.0 and derive a best fit of \alpha _ { i } \sim 1.9 for Seyfert 1 galaxies , consistent with previous studies of intermediate redshift quasars .
If we assume a blue bump model , most sources in our sample have derived temperatures between T _ { BB } = 10 ^ { 5.18 } K to 10 ^ { 5.7 } K , suggesting that the peak of this component spans a large range of energies extending from \sim \lambda 600 Å to \lambda 1900 Å .
In this case , the best fitting peak energy that matches the mid-infrared line ratios of Seyfert 1 galaxies occurs between \sim \lambda 700 – \lambda 1000 Å .
Despite the fact that our results do not rule out the presence of an EUV bump , we conclude that our power-law model produces enough photons with energies > 4 Ry to generate the observed amount of mid-infrared emission in our sample of BAT AGN .