2018MNRAS.476.5075S

We have observed 104 gravitationally lensed quasars at z ∼ 1-4 with Herschel/SPIRE, the largest such sample ever studied. By targeting gravitational lenses, we probe intrinsic far-infrared (FIR) luminosities and star formation rates (SFRs) more typical of the population than the extremely luminous sources that are otherwise accessible. We detect 72 objects with Herschel/SPIRE and find 66 per cent (69 sources) of the sample have spectral energy distributions (SEDs) characteristic of dust emission. For 53 objects with sufficiently constrained SEDs, we find a median effective dust temperature of 38⁺¹²_–5 K. By applying the radio-infrared correlation, we find no evidence for an FIR excess that is consistent with star-formation-heated dust. We derive a median magnification-corrected FIR luminosity of 3.6^+4.8_–2.4 ×10¹¹ L_☉ and median SFR of 120⁺¹⁶⁰_–80 M_☉ yr^–1 for 94 quasars with redshifts. We find ∼10 per cent of our sample have FIR properties similar to typical dusty star-forming galaxies at z ∼ 2-3 and a range of SFRs <20-10 000 M_☉ yr^–1 for our sample as a whole. These results are in line with current models of quasar evolution and suggests a coexistence of dust-obscured star formation and AGN activity is typical of most quasars. We do not find a statistically significant difference in the FIR luminosities of quasars in our sample with a radio excess relative to the radio-infrared correlation. Synchrotron emission is found to dominate at FIR wavelengths for <15 per cent of those sources classified as powerful radio galaxies.