Dusty Tori of Luminous Type 1 Quasars at z \sim 2

Abstract

We present Spitzer infrared spectra and ultra-violet to mid-infrared spectral energy distributions (SEDs) of 25 luminous type 1 quasars at z \sim 2. In general, the spectra show a bump peaking around 3 {\mu}m, and the 10 {\mu}m silicate emission feature. The 3 {\mu}m emission is identified with hot dust emission at its sublimation temperature. We explore two approaches to modeling the SED: (i) using the Clumpy model SED from Nenkova et al. (2008a), and (ii) the Clumpy model SED, and an additional blackbody component to represent the 3 {\mu}m emission. In the first case, a parameter search of \sim 1.25 million Clumpy models shows: (i) if we ignore the UV-to-near-IR SED, models fit the 2-8 {\mu}m region well, but not the 10 {\mu}m feature; (ii) if we include the UV-to-near-IR SED in the fit, models do not fit the 2-8 {\mu}m region. The observed 10 {\mu}m features are broader and shallower than those in the best-fit models in the first approach. In the second case, the shape of the 10 {\mu}m feature is better reproduced by the Clumpy models. The additional blackbody contribution in the 2-8 {\mu}m range allows Clumpy models dominated by cooler temperatures (T < 800K) to better fit the 8-12{\mu}m SED. A centrally concentrated distribution of a small number of torus clouds is required in the first case, while in the second case the clouds are more spread out radially. The temperature of the blackbody component is ~ 1200 K as expected for graphite grains.