We measure the 10 and 18 \mu m silicate features in a sample of 67 local ( z < 0.1 ) type 1 active galactic nuclei ( AGN ) with available Spitzer spectra dominated by non-stellar processes .
We find that the 10 \mu m silicate feature peaks at 10.3 ^ { +0.7 } _ { -0.9 } \mu m with a strength ( Si _ { p } = ln f _ { p } ( spectrum ) /f _ { p } ( continuum ) ) of 0.11 ^ { +0.15 } _ { -0.36 } , while the 18 \mu m one peaks at 17.3 ^ { +0.4 } _ { -0.7 } \mu m with a strength of 0.14 ^ { +0.06 } _ { -0.06 } .
We select from this sample sources with the strongest 10 \mu m silicate strength ( \sigma _ { Si _ { 10 \mu m } } > 0.28 , 10 objects ) .
We carry out a detailed modeling of the IRS/ Spitzer spectra by comparing several models that assume different geometries and dust composition : a smooth torus model , two clumpy torus models , a two-phase medium torus model , and a disk+outflow clumpy model .
We find that the silicate features are well modeled by the clumpy model of Nenkova et al .
2008 , and among all models those including outflows and complex dust composition are the best ( Hoenig et al .
2017 ) .
We note that even in AGN-dominated galaxies it is usually necessary to add stellar contributions to reproduce the emission at the shortest wavelengths .