An ALMA Multiline Survey of the Interstellar Medium of the Redshift 7.5 Quasar Host Galaxy J1342+0928

Abstract

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 × 10 8 M ☉ and a star formation rate of . We have >4 σ detections of the , , and atomic fine structure lines and limits on the , , and emission. We also report multiple limits of CO rotational lines with J up  ≥ 7, as well as a tentative 3.3 σ 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 and lines indicates that the emission arises predominantly from the neutral medium, and we estimate that the photodisassociation regions in J1342+0928 have densities ≲5 × 10 4 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.