Discovery of SiC and Iron Dust around AGB Stars in the Very Metal-poor Sextans a Dwarf Galaxy with JWST: Implications for Dust Production at High Redshift

Abstract Low-resolution infrared spectroscopy from JWST confirms the presence of SiC and likely metallic iron dust around asymptotic giant branch (AGB) stars in the Sextans A dwarf galaxy, which has a metallicity ∼1%–7% Z ⊙ . While metal-poor carbon-rich AGB stars are known to produce copious amounts of amorphous carbon dust owing to the dredge up of newly synthesized carbon, this is the first time that Si- and Fe-bearing dust has been detected at this extreme metallicity. Of the six AGB stars observed, one is an intermediate-mass (∼1.2–4 M ⊙ ) carbon star showing SiC dust, and another is an oxygen-rich M-type star with mass ∼4–5 M ⊙ that is likely undergoing hot bottom burning. The infrared excess of the M-type star is strong, but featureless. We tested multiple dust species, and found that it is best fit with metallic iron dust. Assuming its dust-production rate stays constant over the final 2–3 × 10 4 yr of its evolution, this star will produce ∼0.9–3.7 times the iron dust mass predicted by models, with the range depending on the adopted stellar mass. The implications for dust production in high-redshift galaxies are potentially significant, especially regarding the assumed dust species used in dust evolution models and the timescale of AGB dust formation. Stars on the upper end of the AGB mass range can begin producing dust as early as 30–50 Myr after they form, and they may therefore rival dust production by supernovae at high redshift.

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Publication Details

Journal
The Astrophysical Journal
Published
2025-09-12
DOI
https://doi.org/10.3847/1538-4357/adf06a
Citations
2
Primary Topic
Stellar, planetary, and galactic studies
Type
article
Field-Weighted Citation Impact
2.31

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article

Discovery of SiC and Iron Dust around AGB Stars in the Very Metal-poor Sextans a Dwarf Galaxy with JWST: Implications for Dust Production at High Redshift

R. Sahai, P. A. Whitelock, M. Di Criscienzo, D. A. García–Hernández et al.
2 citations
The Astrophysical Journal
Stellar, planetary, and galactic studies
2.31
article

Discovery of SiC and Iron Dust around AGB Stars in the Very Metal-poor Sextans a Dwarf Galaxy with JWST: Implications for Dust Production at High Redshift

R. Sahai, P. A. Whitelock, M. Di Criscienzo, D. A. García–Hernández, F. Kemper, Martha L. Boyer, G. C. Sloan, S. Srinivasan, J. A. D. L. Blommaert, Kristen B. W. McQuinn, Julia Christine Roman-Duval, Jacco Th. van Loon, Daniel R. Weisz, Iain McDonald, M. A. T. Groenewegen, A. Nanni, Atefeh Javadi, Elizabeth Tarantino, F. Dell’Agli, Evan D. Skillman, R. D. Gehrz, Giada Pastorelli, Olivia Jones, M. Marengo, J. M. Oliveira, Steven Goldman
article en
2 citations

Abstract

Abstract Low-resolution infrared spectroscopy from JWST confirms the presence of SiC and likely metallic iron dust around asymptotic giant branch (AGB) stars in the Sextans A dwarf galaxy, which has a metallicity ∼1%–7% Z ⊙ . While metal-poor carbon-rich AGB stars are known to produce copious amounts of amorphous carbon dust owing to the dredge up of newly synthesized carbon, this is the first time that Si- and Fe-bearing dust has been detected at this extreme metallicity. Of the six AGB stars observed, one is an intermediate-mass (∼1.2–4 M ⊙ ) carbon star showing SiC dust, and another is an oxygen-rich M-type star with mass ∼4–5 M ⊙ that is likely undergoing hot bottom burning. The infrared excess of the M-type star is strong, but featureless. We tested multiple dust species, and found that it is best fit with metallic iron dust. Assuming its dust-production rate stays constant over the final 2–3 × 10 4 yr of its evolution, this star will produce ∼0.9–3.7 times the iron dust mass predicted by models, with the range depending on the adopted stellar mass. The implications for dust production in high-redshift galaxies are potentially significant, especially regarding the assumed dust species used in dust evolution models and the timescale of AGB dust formation. Stars on the upper end of the AGB mass range can begin producing dust as early as 30–50 Myr after they form, and they may therefore rival dust production by supernovae at high redshift.

The Astrophysical JournalVol. 991(1)
Rutgers, The State University of New Jersey (US), Florida State University (US), University of North Carolina at Chapel Hill (US), Institució Catalana de Recerca i Estudis Avançats (ES), Space Telescope Science Institute (US), University of Minnesota (US), Institute of Space Sciences (ES), Jet Propulsion Laboratory (US), Vrije Universiteit Brussel (BE), University of Cape Town (ZA), Universidad de La Laguna (ES), The Open University (GB), Royal Observatory of Belgium (BE), Astronomical Observatory of Rome (IT), University of Manchester (GB), Institut d'Estudis Espacials de Catalunya (ES), National Centre for Nuclear Research (PL), Royal Observatory (GB), South African Radio Astronomy Observatory (ZA), Université Bourgogne Franche-Comté (FR), Collurania Teramo Observatory (IT), Instituto de Astrofísica de Canarias (ES), Institute for Research in Fundamental Sciences (IR), Osservatorio Astronomico di Padova (IT), UK Astronomy Technology Centre (GB), Keele University (GB), Universidad Nacional Autónoma de México (MX), University of California, Berkeley (US)
National Aeronautics and Space Administration, California Institute of Technology, Space Telescope Science Institute, Ministerio de Ciencia, Innovación y Universidades, National Research Foundation, Narodowe Centrum Nauki, Jet Propulsion Laboratory, Science and Technology Facilities Council, European Regional Development Fund, Agencia Estatal de Investigación
Openalex Percentile: Top 10%
Stellar, planetary, and galactic studies
2.31
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