Star formation in quasar hosts and the origin of radio emission in
  radio-quiet quasars
  Radio emission from radio-quiet quasars may be due to star formation in the
quasar host galaxy, to a jet launched by the supermassive black hole, or to
relativistic particles accelerated in a wide-angle radiatively-driven outflow.
In this paper we examine whether radio emission from radio-quiet quasars is a
byproduct of star formation in their hosts. To this end we use infrared
spectroscopy and photometry from Spitzer and Herschel to estimate or place
upper limits on star formation rates in hosts of ~300 obscured and unobscured
quasars at z<1. We find that low-ionization forbidden emission lines such as
[NeII] and [NeIII] are likely dominated by quasar ionization and do not provide
reliable star formation diagnostics in quasar hosts, while PAH emission
features may be suppressed due to the destruction of PAH molecules by the
quasar radiation field. While the bolometric luminosities of our sources are
dominated by the quasars, the 160 micron fluxes are likely dominated by star
formation, but they too should be used with caution. We estimate median star
formation rates to be 6-29 Msun/year, with obscured quasars at the high end of
this range. This star formation rate is insufficient to explain the observed
radio emission from quasars by an order of magnitude, with log(L_radio,
observed/L_radio, SF)=0.6-1.3 depending on quasar type and star formation
estimator. Although radio-quiet quasars in our sample lie close to the 8-1000
micron infrared / radio correlation characteristic of the star-forming
galaxies, both their infrared emission and their radio emission are dominated
by the quasar activity, not by the host galaxy.
