An ALMA multi-line survey of the interstellar medium of the redshift 7.5 quasar host galaxy J1342+0928

We use ALMA 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. The Rayleigh-Jeans tail of the dust continuum is well sampled with eight different spectral setups, and from a modified black body fit we obtain an emissivity coefficient of β = 1.85 ± 0.3. Assuming a standard dust temperature of 47K we derive a dust mass of M_dust= 0.35 × 10⁸Mo and a star formation rate of 150 ± 30Mo yr^-1. We have > 4δ detections of the [CII]_158μm, [OIII]_88μmand [NII]_122μmatomic fine structure lines and limits on the [CI]_369μm, [OI]_146μmand [NII]2_05μmemission. We also report multiple limits of CO rotational lines with Jup 7, as well as a tentative 3.3μ detection of the stack of four CO lines (Jup = 11; 10; 8 and 7). We find line deficits that are in agreement with local ultra luminous infrared galaxies. Comparison of the [NII]_122μmand [CII]1_58μmlines indicates that the [CII]158 μm emission arises predominantly from the neutral medium, and we estimate that the photo-disassociation regions in J1342+0928 have densities . 5 ≲ 104 cm^-3. The data suggest that ∼ 16% of hydrogen is in ionized form and that the HII regions have high electron densities of ne > 180 cm^-3. Our observations favor a low gas-to-dust ratio of < 100, and a metallicity of the interstellar medium 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.