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High Signal-to-Noise Ratio Mid-Infrared Quasar Spectral Templates
Journal article   Open access

High Signal-to-Noise Ratio Mid-Infrared Quasar Spectral Templates

Allison R Hill, S. C Gallagher, R. P Deo, E Peeters and Gordon T Richards
Proceedings of the International Astronomical Union, v 9(S304)
15 Jan 2014
DOI: https://doi.org/10.1017/S1743921314004153
url
https://doi.org/10.1017/s1743921314004153View
Published, Version of Record (VoR)Maybe Open Access (Publisher Bronze),  Open
url
https://doi.org/10.1017/S1743921314004153View
Published, Version of Record (VoR) Open

Abstract

Mid-infrared (MIR) quasar spectra exhibit a suite of emission features including high ionization coronal lines from the narrow line region (NLR) illuminated by the ionizing continuum, and hot dust features from grains, as well as polycyclic aromatic hydrocarbons (PAH) features from star formation in the host galaxy. Few features are detected in most spectra because of typically low signal-to-noise ratio (S/N) data. By generating spectral composites in three different luminosity bins from over 180 Spitzer Infrared Spectrograph (IRS) observations, we boost the S/N and reveal important features in the complex spectra. We detect high-ionization, forbidden emission lines in all templates, PAH features in all but the most luminous objects, and broad silicate and graphite features in emission whose strength increases relative to the continuum with luminosity. We find that the intrinsic quasar spectrum for all luminosity templates is consistent, and the differences in the spectra can be explained by host galaxy contamination in the lower luminosity templates. We also posit that star formation may be active in most quasar host galaxies, but the spectral features of star formation are only detectable if the quasar is faint.

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