An Analysis of Quasar Mid-Infrared Spectra

We analyzed the SPITZER IRS mid-infrared spectra of a sample of 42 quasars. We measure continua and emission-line features, including continua near 5.5 μm, 10 μm silicate-emission feature, and several narrow emission lines(S IV 10.5 μm, Ne V 14.3 μm, Ne III 15.6 μm, and O IV 25.9 μm). There exists a strong correlation between 5.5 μm continuum flux and the narrow emission-line fluxes, indicating that the 5.5 μm continuum is also powered directly by AGN photons and its flux can be used as a valid indicator of AGN power. We find no correlation between Eigenvector I and 10 μm silicate-emission feature in Mid-IR, implying that in quasars most of dust cannot exist in or close to narrow-line regions.