Evidence for inefficient dust production in a massive, metal-rich galaxy at $z=7.13$ uncovered by JWST and ALMA

Recent observations show a remarkably rapid buildup of cosmic dust in high-redshift galaxies, with complex dust compositions and large abundances already appearing at z>6. This study presents a comprehensive joint analysis of James Webb Space Telescope (JWST) and Atacama Large Millimetre/submillimetre Array (ALMA) observations of the highly magnified (μ = 9.6), dusty 'normal' galaxy A1689-zD1 at z=7.13.

The authors perform detailed spectro-photometric modeling of the rest-frame UV to far-infrared spectral energy distribution (SED) based on archival photometry of the source. They also report new rest-frame optical strong-line measurements and metallicity estimates from recent JWST/NIRSpec IFU data.

Despite its substantial dust mass, M_dust ~ 1.5×10^7 M_sun, A1689-zD1 has remarkably low dust-to-gas and dust-to-metal mass ratios: DTG = (5.5+3.5−1.2)×10^−4 and DTM = (6.2+4.2−2.6)×10^−2. These low ratios arise because of its high metallicity, 12+log(O/H) = 8.36±0.10, and substantial gas mass, M_gas = (2.8+0.2−1.7)×10^10 M_sun, inferred from the [C II] luminosity and bounded by its dynamics. The DTG and DTM values are an order of magnitude lower than expected for galaxies in the local universe with similar chemical enrichment. These low relative measurements are also consistent with the deficit observed in the A_V/N_HI ratio of A1689-zD1 along the line of sight.

The deviation in DTG and DTM appears to be ubiquitous in other metal-rich galaxies at similar redshifts, z≳6. This suggests that the processes that form and destroy dust at later times, or the dust emissivity itself, are likely different for galaxies in the early Universe.