First Constraints on Dense Molecular Gas at z=7.5149 from the Quasar Poniuaena

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 (Poniua'ena) at z = 7.5149, obtained with the NOrthern Extended Millimeter Array. Poniua'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(H-2) = (2.2 +/- 0.2) x 10(10) M-circle dot, assuming a CO spectral line energy distribution typical of high-redshift quasars and a conversion factor alpha = 0.8 M-circle dot(Kkms(-1)pc(2))(-1) . We model the cold dust spectral energy distribution to derive a dust mass of M-dust = (1.7 +/- 0.6) x 10(8) M-circle dot and thus, a gas-to-dust ratio similar to 130. Both the gas and dust mass are remarkably similar to the reservoirs found for luminous quasars at z similar to 6-7. We use the CO detection to derive an estimate of the cosmic mass density of H2, O-H2 Omega(Pi 2) similar or equal to 1.31x10(-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.