Recent observations of quasars, Mrk 335 and the HST quasar composite spectrum, have indicated that many quasars have remarkably soft ionizing continua (f ∝ ~ ν-2, 13.6-100 eV). We point out that the number of photons with hν > 54.4 eV is insufficient to create the observed strengths of the He II emission lines. While the numbers of photons which energize C IV λ1549 and O VI λ1034 are sufficient, even the most efficiently emitting clouds for these two lines must each cover at least 20%-40% of the source. If the typical quasar ionizing continuum is indeed this soft, then we must conclude that the broad emission line clouds must see a very different (harder) continuum than we see. The other viable possibility is that the UV-EUV SED is double peaked, with the second peaking near 54 eV, its Wien tail being the observed soft X-ray excess.
Digital Object Identifier (DOI)
Korista, Kirk; Ferland, Gary J.; and Baldwin, Jack, "Do the Broad Emission Line Clouds See the Same Continuum That We See?" (1997). Physics and Astronomy Faculty Publications. 120.