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 <SUB>dust</SUB> = 0.35 × 10<SUP>8</SUP> M <SUB>☉</SUB> and a star formation rate of 150+/- 30 {M}<SUB>☉ </SUB> {yr}}<SUP>-1</SUP>. We have >4σ detections of the {[{{C}}{{II}}]}<SUB>158μ {{m</SUB>}}, {[{{O}}{{III}}]}<SUB>88μ {{m</SUB>}}, and {[{{N}}{{II}}]}<SUB>205μ {{m</SUB>}} atomic fine structure lines and limits on the {[{{C}}{{I}}]}<SUB>369μ {{m</SUB>}}, {[{{O}}{{I}}]}<SUB>146μ {{m</SUB>}}, and {[{{N}}{{II}}]}<SUB>205μ {{m</SUB>}} emission. We also report multiple limits of CO rotational lines with J <SUB>up</SUB> ≥ 7, as well as a tentative 3.3σ detection of the stack of four CO lines (J <SUB>up</SUB> = 11, 10, 8, and 7). We find line deficits that are in agreement with local ultra-luminous infrared galaxies. Comparison of the {[{{N}}{{II}}]}<SUB>205μ {{m</SUB>}} and {[{{C}}{{II}}]}<SUB>158μ {{m</SUB>}} lines indicates that the {[{{C}}{{II}}]}<SUB>158μ {{m</SUB>}} emission arises predominantly from the neutral medium, and we estimate that the photodisassociation regions in J1342+0928 have densities ≲5 × 10<SUP>4</SUP> cm<SUP>-3</SUP>. The data suggest that ∼16% of hydrogen is in ionized form and that the H II regions have high electron densities of n <SUB> e </SUB> > 180 cm<SUP>-3</SUP>. 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.