Nanodiamantes y el Quiebre en la Distribución de Energía de Quasares

The quasar spectral energy distribution (SED) in the UV is characterized by a sharp break near 1000 A. The SED (in Fnu) of quasars can be described by a broken powerlaw. Telfer et al. 2002 showed, using a composite quasar spectrum, that the powerlaw index changes from -0.6 in the near UV (longward of 1000 A) to -1.7 in the far-UV. This means that the quasar SED is very soft, which complicates the modeling of the high excitation emission lines using photoionization models. We have calculated extinction curves using grains that are made of crystallite nanodiamonds, either terrestrial or extracted from a primitive meteorite (Allende). We show that such dust reproduce not only the quasar UV break, it also accounts for the flux rise at ~700 A observed in 4 quasars. One benefit of the dust interpretation for the UV break is that it resolves the problem as to why objects apparently devoid of far-UV flux (with an extreme UV break) can still generate luminous high excitation emission lines.