Distant galaxy A1689-zD1 found to have unusually low dust-to-gas ratio
JWST/NIRCam false color RGB image cutout (blue: F150W; green: F277W; red: F444W), overlaid with [C ii]-158 µm emission contours showing 3, 5, 7, 10σ (white solid lines). A scale bar is displayed in the image plane. Credit: arXiv (2025). DOI: 10.48550/arxiv.2510.07936
Using the James Webb Space Telescope (JWST) and the Atacama Large Millimeter/submillimeter Array (ALMA), an international team of astronomers has made comprehensive, multi-wavelength observations of a distant massive galaxy known as A1689-zD1.
The new observations, detailed in an article published October 9 on the preprint server arXivprovide important information on the properties of the galaxy, particularly with regard to dust production in this system.
A1689-zD1 is a massive, bright, highly lensed galaxy with a redshift of approximately 7.13. It has a diameter of about 3,000 light years and its stellar mass is estimated at some 2.6 billion solar masses.
Previous observations of A1689-zD1 showed that it had a near-solar metallicity and contained a substantial amount of dust, with an estimated mass of 15 million solar masses. For this reason, A1689-zD1 is an excellent place to study the existence of interstellar dust in early cosmic epochs.
That’s why a group of astronomers led by Kasper E. Heintz from the University of Copenhagen, Denmark, decided to explore dust content with JWST and ALMA.
“We revisited this galaxy to evaluate the components of baryonic matter in the ISM [interstellar medium]with particular emphasis on limiting the accumulation of cosmic dust,” the researchers explained.
Hintz’s team performed ultraviolet to far-infrared modeling of the spectral energy distribution (SED) of A1689-zD1 to determine its stellar mass, dust mass, visual attenuation, and star formation rate. ALMA observations were also used to constrain the total dynamic mass of the source and infer the gas mass using common gas tracers but limited by the overall dynamics of the system.
The study found that although A1689-zD1 has a significant dust mass, its dust-to-gas (DTG) and dust-to-metal (DTM) mass ratios are remarkably low, at a level of 0.00051 and 0.061, respectively. Astronomers note that this is due to A1689-zD1’s high metallicity and its large gas mass, estimated at 28 billion solar masses.
Therefore, the DTG and DTM mass ratios for A1689-zD1 are an order of magnitude lower than those found in the Milky Way and the Large Magellanic Cloud (LMC) or the Small Magellanic Cloud (SMC). These ratios also suggest that the neutral atomic hydrogen (HI) gas in the line of sight of A1689-zD1 is relatively dust-poor compared to its chemical enrichment.
The authors of the article conclude that the results obtained indicate a potential change in the relative abundance of dust or in the composition of the first galaxies.
“We find that this discrepancy in the DTG and DTM mass ratios appears to be pervasive in other metal-rich galaxies with similar redshifts, z ≳ 6. This suggests that the processes that later form and destroy dust, or the emissivity of dust itself, are radically different for galaxies in the early universe,” the scientists conclude.
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More information:
Kasper E. Heintz et al, Inefficient dust production in a massive, metal-rich galaxy at z = 7.13 discovered by JWST and ALMA, arXiv (2025). DOI: 10.48550/arxiv.2510.07936
Journal information:
arXiv
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