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The star formation activity of the host galaxies of active galactic nuclei provides valuable insights into the complex interconnections between black hole growth and galaxy evolution. A major obstacle arises from the difficulty of estimating accurate star formation rates (SFRs) in the presence of a strong active galactic nucleus. Analyzing the 1–500 μm spectral energy distributions and high-resolution mid-infrared spectra of low-redshift (z < 0.5) Palomar–Green quasars with bolometric luminosity of ∼1044.5–1047.5 erg s−1, we find, from comparison with an independent SFR indicator based on [Ne II ] 12.81 μm and [Ne III ] 15.56 μm, that the torus-subtracted, total infrared (8–1000 μm) emission yields robust SFRs in the range of ∼1–250 M⊙ yr−1. Combined with available stellar mass estimates, the vast majority (∼75%–90%) of the quasars lie on or above the main sequence of local star-forming galaxies, including a significant fraction (∼50%–70%) that would qualify as starburst systems. This is further supported by the high star formation efficiencies derived from the gas content inferred from the dust masses. Inspection of high-resolution Hubble Space Telescope images reveals a wide diversity of morphological types, including a number of starbursting hosts that have not experienced significant recent dynamical perturbations. The origin of the high star formation efficiency is unknown. [ABSTRACT FROM AUTHOR]

The tori around active galactic nuclei (AGN) are potential formation sites for large amounts of dust, and they may help resolve the so-called dust budget crisis at high redshift. We investigate the dust composition in 53 of the 87 Palomar Green (PG) quasars showing the 9.7 μ m silicate feature in emission. By simultaneously fitting the mid-infrared spectroscopic features and the underlying continuum, we estimate the mass fraction in various amorphous and crystalline dust species. We find that the dust consists predominantly of alumina and amorphous silicates, with a small fraction in crystalline form. The mean crystallinity is 8 ± 6%, with more than half of the crystallinities greater than 5%, well above the upper limit determined for the Galaxy. Higher values of crystallinity are found for higher oxide fractions and for more luminous sources. [ABSTRACT FROM AUTHOR]