High Star Formation Rates of Low Eddington Ratio Quasars at $z\gtrsim6$
  Recent simulation studies suggest that the supermassive black hole (SMBH)
growth in the early universe may precede the prolonged intense star formation
within its host galaxy, instead of quasars appearing after the obscured dusty
star formation phase. If so, high-redshift quasars with low Eddington ratios
($\lambda_{\rm Edd}$) would be found in actively star-forming hosts with a star
formation rate (SFR) of $>100~M_{\odot}$ yr$^{-1}$. We present the sub-mm
observations of IMS J2204+0112, a faint quasar with a quasar bolometric
luminosity of $L_{\rm bol}=4.2\times10^{12}~L_{\odot}$ and a low $\lambda_{\rm
Edd}$ of only 0.1 at $z\sim6$, carried out with the Atacama Large
Millimeter/submillimeter Array (ALMA). From its sub-mm fluxes, we measure the
rest-frame far-infrared (FIR) luminosity of $L_{\rm
FIR}=(3$--$4)\times10^{12}~L_{\odot}$. Interestingly, the derived host galaxy's
SFR is $\sim500$--$700~M_{\odot}$ yr$^{-1}$, an order of magnitude higher than
those of the $L_{\rm bol}$-matched $z\gtrsim6$ quasars with high $\lambda_{\rm
Edd}$. Similar FIR excesses are also found for five $z\gtrsim6$
low-$\lambda_{\rm Edd}$ quasars ($\lambda_{\rm Edd}<0.2$) in the literature. We
show that the overall SFR, $M_{\rm BH}$, and $\lambda_{\rm Edd}$ distributions
of these and other sub-mm-detected quasars at $z\gtrsim6$ can be explained with
the evolutionary track of high-redshift quasars in a simulation study where low
$\lambda_{\rm Edd}$ and high SFR quasars are expected at the end of the SMBH
growth. This suggests that the nuclear activities of the low $\lambda_{\rm
Edd}$, high $L_{\rm FIR}$ quasars are on the brink of being turned off, while
their host galaxies continue to form the bulk of their stars at SFR
$>100~M_{\odot}$ yr$^{-1}$.
