2011ApJ...729..108D

We present Spitzer infrared (IR) spectra and ultraviolet (UV) to mid-IR spectral energy distributions (SEDs) of 25 luminous type 1 quasars at z ∼ 2. In general, the spectra show a bump peaking around 3 µm and the 10 µm silicate emission feature. The 3 µm emission is identified with hot dust emission at its sublimation temperature. We explore two approaches to modeling the SED: (1) using the CLUMPY model SED from Nenkova et al. and (2) the CLUMPY model SED and an additional blackbody component to represent the 3 µm emission. In the first case, a parameter search of ∼1.25 million CLUMPY models shows that (1) if we ignore the UV-to-near-IR SED, models fit the 2-8 µm region well, but not the 10 µm feature; (2) if we include the UV-to-near-IR SED in the fit, models do not fit the 2-8 µm region. The observed 10 µm 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 µm feature is better reproduced by the CLUMPY models. The additional blackbody contribution in the 2-8 µm range allows CLUMPY models dominated by cooler temperatures (T < 800 K) to better fit the 8-12 µm 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.