2023ApJ...954L..10F

We report the detection of CO(6-5) and CO(7-6) and their underlying continua from the host galaxy of quasar J100758.264+211529.207 (Pōniuā'ena) at z = 7.5149, obtained with the NOrthern Extended Millimeter Array. Pōniuā'ena belongs to the HYPerluminous quasars at the Epoch of ReionizatION sample of 18 z > 6 quasars selected to be powered by supermassive black holes, which experienced the fastest mass growth in the first cosmic gigayear. The one reported here is the highest-redshift measurement of the cold and dense molecular gas to date. The host galaxy is unresolved, and the line luminosity implies a molecular reservoir of M(H₂) = (2.2 ± 0.2) × 10¹⁰M_⊙, assuming a CO spectral line energy distribution typical of high-redshift quasars and a conversion factor α = 0.8 ${M}_{\odot }{({\rm{K}}\,\mathrm{km}\,{{\rm{s}}}^{-1}\,{\mathrm{pc}}^{2})}^{-1}$. We model the cold dust spectral energy distribution to derive a dust mass of M_dust = (1.7 ± 0.6) × 10⁸M_⊙ and thus, a gas-to-dust ratio ∼130. Both the gas and dust mass are remarkably similar to the reservoirs found for luminous quasars at z ∼ 6-7. We use the CO detection to derive an estimate of the cosmic mass density of H₂, ${{\rm{\Omega }}}_{{{\rm{H}}}_{2}}\simeq 1.31\times {10}^{-5}$. This value is in line with the general trend suggested by literature estimates at z < 7 and agrees fairly well with the latest theoretical expectations of nonequilibrium molecular-chemistry cosmological simulations of cold gas at early times.