We present a new analysis of the Palomar-Green quasar sample based on Spitzer and Herschel observations. (i) Assuming polycyclic aromatic hydrocarbon (PAH)-based star formation luminosities (LSF) similar to Symeonidis et al. (S16), we find mean and median intrinsic active galactic nucleus (AGN) spectral energy distributions (SEDs). These, in the far-infrared (FIR), appear hotter and significantly less luminous than the S16 mean intrinsic AGN SED. The differences are mostly due to our normalization of the individual SED that properly accounts for a small number of very FIR-luminous quasars. Our median, PAH-based SED represents ~6 per cent increase on the 1-243 μm luminosity of the extended Mor & Netzer (EM12) torus SED, while S16 find a significantly larger difference. It requires large-scale dust with T ~ 20-30 K, which, if optically thin and heated by the AGN, would be outside the host galaxy. (ii) We also explore the black hole and stellar mass growths, using LSF estimates from fitting Herschel/PACS observations after subtracting the EM12 torus contribution. We use rough estimates of stellar mass, based on scaling relations, to divide our sample into groups: on, below and above the star formation main sequence (SFMS). Objects on the SFMS show a strong correlation between star formation luminosity and AGN bolometric luminosity, with a logarithmic slope of ~0.7. Finally, we derive the relative duty cycles of this and another sample of very luminous AGN at z=2-3.5. Large differences in this quantity indicate different evolutionary pathways for these two populations characterized by significantly different black hole masses.
- Galaxies: active
- Galaxies: star formation
- Quasars: supermassive black holes