The evolution of star formation in quasar host galaxies

We have used far-infrared data from IRAS, ISO, SWIRE, SCUBA and 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 < IAB < −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 100μm fluxes at < 1 Jy are overestimated by ∼ 30%. We find evidence for a correlation between star formation in quasar hosts and the quasar optical luminosities, varying as SFR ∝ L opt at any fixed redshift below z = 2. We also find evidence for evolution of the mean star formation rate in quasar host galaxies, scaling as (1+z) at z < 2 for any fixed quasar I-band absolute magnitude fainter than −28. We find no evidence for any correlation between star formation rate 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.