The evolution of star formation in quasar host galaxies

We have used far-infrared data from IRAS, Infrared Space Observatory (ISO), Spitzer Wide-Area Infrared Extragalactic (SWIRE), Submillimetre Common User Bolometer Array (SCUBA) and Max-Planck Millimetre Bolometer (MAMBO) to constrain statistically the mean far-infrared luminosities of quasars. Our quasar compilation at redshifts 0 < z < 6.5 and I-band luminosities -20 < I-AB < -32 is the first to distinguish evolution from quasar luminosity dependence in such a study. We carefully cross-calibrate IRAS against Spitzer and ISO, finding evidence that IRAS 100-mu m fluxes at < 1 Jy are overestimated by similar to 30 per cent. We find evidence for a correlation between star formation in quasar hosts and the quasar optical luminosities, varying as star formation rate (SFR) proportional to L-opt(0.44 +/- 0.07) at any fixed redshift below z = 2. We also find evidence for evolution of the mean SFR in quasar host galaxies, scaling as (1 + z)(1.6 +/- 0.3) at z < 2 for any fixed quasar I-band absolute magnitude fainter than -28. We find no evidence for any correlation between SFR and black hole mass at 0.5 < z < 4. Our data are consistent with feedback from black hole accretion regulating stellar mass assembly at all redshifts.