Star formation rates in luminous quasars at 2 < z < 3
Clements, David L.; Chapman, Scott; Vieira, Joaquin; Lacy, Mark; Cooray, Asantha; Schulz, Bernhard; Béthermin, Matthieu; Wang, Lingyu; Hatziminaoglou, Evanthia; Scott, Douglas; Farrah, Duncan; Rigopoulou, Dimitra; Efstathiou, Andreas; Oliver, Sebastian; Pitchford, Lura K.; Pérez-Fournon, Ismael; Petty, Sara M.; Symeonidis, Myrto; Hurley, Peter; Ibar, Eduardo; Viero, Marco; Page, Mathew J.; Harris, Kathryn; Anderson, Nick; Feltre, Anne
United States, Spain, Germany, Canada, United Kingdom, Cyprus, France, Chile, Netherlands
Abstract
We investigate the relation between star formation rates (dot{{M}}_s) and AGN properties in optically selected type 1 quasars at 2 < z < 3 using data from Herschel and the SDSS. We find that dot{{M}}_s remains approximately constant with redshift, at 300 ± 100 M⊙ yr-1. Conversely, dot{{M}}_s increases with AGN luminosity, up to a maximum of ∼ 600 M⊙ yr-1, and with C IV FWHM. In context with previous results, this is consistent with a relation between dot{{M}}_s and black hole accretion rate (dot{{M}}_{bh}) existing in only parts of the z-dot{{M}}s-dot{{M}}_{bh} plane, dependent on the free gas fraction, the trigger for activity, and the processes that may quench star formation. The relations between dot{{M}}_s and both AGN luminosity and C IV FWHM are consistent with star formation rates in quasars scaling with black hole mass, though we cannot rule out a separate relation with black hole accretion rate. Star formation rates are observed to decline with increasing C IV equivalent width. This decline can be partially explained via the Baldwin effect, but may have an additional contribution from one or more of three factors; MI is not a linear tracer of L2500, the Baldwin effect changes form at high AGN luminosities, and high C IV EW values signpost a change in the relation between dot{{M}}_s and dot{{M}}_{bh}. Finally, there is no strong relation between dot{{M}}_s and Eddington ratio, or the asymmetry of the C IV line. The former suggests that star formation rates do not scale with how efficiently the black hole is accreting, while the latter is consistent with C IV asymmetries arising from orientation effects.