2019ApJ...881...63N

We use Atacama Large Millimeter Array observations of the host galaxy of the quasar ULAS J1342+0928 at z = 7.54, to study the dust continuum and far-infrared lines emitted from its interstellar medium (ISM). The Rayleigh-Jeans tail of the dust continuum is well sampled with eight different spectral setups, and from a modified blackbody fit we obtain an emissivity coefficient of β = 1.85 ± 0.3. Assuming a standard dust temperature of 47 K we derive a dust mass of M_dust = 0.35 x 10⁸ M_☉ and a star formation rate of 150±30M_☉yr^–1. We have >4σ detections of the [CII]_158µm_, [OIII]_88µm_, and [NII]_205µm_ atomic fine structure lines and limits on the [CI]_369µm_, [OI]_146µm_, and [NII]_205µm_ emission. We also report multiple limits of CO rotational lines with J_up >= 7, as well as a tentative 3.3σ detection of the stack of four CO lines (J_up = 11, 10, 8, and 7). We find line deficits that are in agreement with local ultra-luminous infrared galaxies. Comparison of the [NII]_205µm_ and [CII]_158µm_ lines indicates that the [CII]_158µm_ emission arises predominantly from the neutral medium, and we estimate that the photodisassociation regions in J1342+0928 have densities <=5 x 10⁴ cm^–3. The data suggest that ∼16% of hydrogen is in ionized form and that the H II regions have high electron densities of n_e > 180 cm^–3. Our observations favor a low gas-to-dust ratio of <100, and a metallicity of the ISM comparable to the solar value. All the measurements presented here suggest that the host galaxy of J1342+0928 is highly enriched in metal and dust, despite being observed just 680 Myr after the big bang.