Far-infrared and Molecular CO Emission From the Host Galaxies of Faint
  Quasars at z~6
  We present new millimeter and radio observations of nine z~6 quasars
discovered in deep optical and near-infrared surveys. We observed the 250 GHz
continuum in eight of the nine objects and detected three of them. New 1.4 GHz
radio continuum data have been obtained for four sources, and one has been
detected. We searched for molecular CO (6-5) line emission in the three 250 GHz
detections and detected two of them. We study the FIR and radio emission and
quasar-host galaxy evolution with a sample of 18 z~6 quasars that are faint at
UV/optical wavelengths (rest-frame 1450A magnitudes of m_1450\ge20.2). The
average FIR-to-AGN UV luminosity ratio of this faint quasar sample is about two
times higher than that of the bright quasars at z~6 (m_1450<20.2). A fit to the
average FIR and AGN bolometric luminosities of both the UV/optically faint and
bright z~6 quasars, and the average luminosities of samples of submillimeter
/millimeter-observed quasars at z~2 to 5, yields a relationship of L_{FIR}
{L_{bol}}^{0.62}. Five of the 18 faint z~6 quasars have been detected at 250
GHz. These 250 GHz detections, as well as most of the millimeter-detected
optically bright z~6 quasars, follow a shallower trend of L_{FIR}
{L_{bol}}^{0.45} defined by the starburst-AGN systems in local and high-z
universe. The millimeter continuum detections in the five objects and molecular
CO detections in three of them reveal a few x10^8 M_sun of FIR-emitting warm
dust and 10^10 M_sun of molecular gas in the quasar host galaxies. All these
results argue for massive star formation in the quasar host galaxies, with
estimated star formation rates of a few hundred M_sun yr^{-1}. Additionally,
the higher FIR-to-AGN luminosity ratio found in these 250 GHz-detected faint
quasars also suggests a higher ratio between star formation rate and
supermassive black hole accretion rate than the UV/optically most luminous
quasars at z~6.
