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.

Document Type


Publication Date


Notes/Citation Information

Published in The Astrophysical Journal, v. 729, no. 2, 108, p. 1-13.

© 2011. The American Astronomical Society. All rights reserved. Printed in the U.S.A.

The copyright holder has granted permission for posting the article here.

Digital Object Identifier (DOI)


Funding Information

Support for this work was provided by NASA through awards (RSA's 1353801 and 1365236) issued by JPL/Caltech. G.T.R. was supported in part by an Alfred P. Sloan Research Fellowship. S.C.G. thanks the National Science and Engineering Research Council of Canada for support. The IRS was a collaborative venture between Cornell University and Ball Aerospace Corporation funded by NASA through the Jet Propulsion Laboratory and Ames Research Center.