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| Figure 7. Chandra sources in the HDFN (left) and use of mid-infrared neon fine structure lines to probe their nature. Ne V is not excited by hot stellar spectra, but is by the hard UV spectra of AGNs. Hence, NeV(14.3 m m) /NeIII(15.6m m)vs. NeII(12.8m m)/NeIII(15.6) distinguishes the two types and gives the slope of the UV continuum. The ratios are virtually extinction independent, as shown by the vector for visual extinction of 100 magnitudes. Line ratios from Voit (1992). |