Spitzer quasar and ULIRG evolution study (QUEST).: II.: The spectral energy distributions of palomar-green quasars

This is the second paper studying the QSOs in the Spitzer QUEST sample. Previously we presented new PAH measurements and argued thatmost of the observed far- infrared ( FIR) radiation is due to star- forming activity. Here we present spectral energy distributions ( SEDs) by supplementing our data with optical, NIR, and FIR observations. We define two subgroups, of weak FIR'' and strong FIR'' QSOs, and a third group of FIR nondetections. Assuming a starburst origin for the FIR, we obtain intrinsic'' active galactic nucleus (AGN) SEDs by subtracting a starburst template from the mean SEDs. The resulting SEDs are remarkably similar for all groups. They show three distinct peaks corresponding to two silicate emission features and a 3 mu m bump, whichwe interpret as the signature of the hottestAGN dust. They also display drops beyond similar to 20 mu m that we interpret as the signature of the minimumtemperature (similar to 200 K) dust. This component must be optically thin to explain the silicate emission and the slope of the long- wavelength continuum. We discuss the merits of an alternative model in which most of the FIR emission is due to AGN heating. Such models are unlikely to explain the properties of our QSOs, but they cannot be ruled out formore luminous objects. We also find correlations between the luminosity at 5100 angstrom and two infrared starburst indicators: L(60 mu m) and L( PAH 7: 7 mu m). The correlation of L(5100 angstrom) with L( 60 mu m) can be used to measure the relative growth rates and lifetimes of the black hole and the new stars.