Search

We present ALMA Band 9 continuum observation of the ultraluminous quasi-stellar object (QSO) SDSS J0100+2802 providing a ∼10 σ detection at ∼670 GHz. SDSS J0100+2802 is the brightest QSO with the most massive supermassive black hole (SMBH) known at z > 6, and we study its dust spectral energy distribution in order to determine the dust properties and the star formation rate (SFR) of its host galaxy. We obtain the most accurate estimate so far of the temperature, mass, and emissivity index of the dust, which are T _dust = 48.4 ± 2.3 K, M _dust = (2.29 ± 0.83) × 10 ^7 M _⊙ , and β = 2.63 ± 0.23, respectively. This allows us to measure the SFR with the smallest statistical error for this QSO, SFR = 265 ± 32 M _⊙ yr ^−1 . Our results enable us to evaluate the relative growth of the SMBH and host galaxy of J0100+2802. We find that the SMBH is dominating the process of black-hole galaxy growth in this QSO at z = 6.327, when the universe was 865 Myr old. Such unprecedented constraints on the host-galaxy SFR and dust temperature can only be obtained through high-frequency observations and highlight the importance of ALMA Band 9 to obtain a robust overview of the buildup of the first quasars’ host galaxies at z > 6.

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 (H _2 ) = (2.2 ± 0.2) × 10 ^10 M _⊙ , 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) × 10 ^8 M _⊙ 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 H _2 , ${{\rm{\Omega }}}_{{{\rm{H}}}_{2}}\simeq 1.31\times {10}^{-5}$ . 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.