Star Formation and ISM Properties in Host Galaxies of Three Far-infrared Luminous Quasars at $z\sim 6$

We present Karl G. Jansky Very Large Array (VLA) observations of the CO (2$-$1) line emission towards three far-infrared luminous quasars at $z\sim 6$: SDSS J231038.88$+$185519.7 and SDSS J012958.51$-$003539.7 with $\sim 0^{\mathrm{\prime }\mathrm{\prime }}6$ resolution and SDSS J205406.42$-$000514.8 with $\sim 2^{\mathrm{\prime }\mathrm{\prime }}1$ resolution. All three sources are detected in the CO (2$-$1) line emission – one source is marginally resolved, and the other two appear as point sources. Measurements of the CO (2$-$1) line emission allow us to calculate the molecular gas mass even without a CO excitation model. The inferred molecular gas masses are (0.8$-$4.3) $\times$ 10${}^{10}$ $M_{\odot }$. The widths and redshifts derived from the CO (2$-$1) line are consistent with previous CO (6$-$5) and [\ion{C}{2}] measurements. We also report continuum measurements using the Herschel for SDSS J231038.88$+$185519.7 and SDSS J012958.51$-$003539.7, and for SDSS J231038.88+185519.7, data obtained at $\sim 140$ and $\sim 300$ GHz using the Atacama Large Millimeter/submillimeter Array (ALMA). In the case of SDSS J231038.88+185519.7, we present a detailed analysis of the spectral energy distribution and derive the dust temperature ($\sim 40$ K), the dust mass ($\sim {10}^9$ $M_{\odot }$), the far-infrared luminosity (8$-$1000 $\mu$m; $\sim {10}^{13}$ $L_{\odot }$) and the star formation rate (2400$-$2700 $M_{\odot }$ yr${}^{-1}$). Finally, an analysis of the photo-dissociation regions associated with the three high redshift quasars indicates that the interstellar medium in these sources has similar properties to local starburst galaxies.