Dust and PAHs in late-stage galaxy evolution: Imprints of TP-AGB dust injection, grain growth and AGN feedback in high-z quiescent galaxies with JWST and ALMA

D. Donevski, A. Nanni, K. E. Whitaker, A. W. S. Man, A. Faisst, A. Lapi, I. García-Bernete, M. Romano, T. Petrushevska, G. Gururajan, G. Lorenzon, D. Narayanan

First listed 2026-08-31 | Last updated 2026-09-01

Abstract

A major unknown in late-stage galaxy evolution is what regulates the cold interstellar medium (ISM) after quenching, a question central to interpreting molecular gas, dust, and stellar content in quiescent galaxies (QGs) now probed by ALMA and JWST to $z\sim7$. We present the first semi-analytic model that follows the coupled post-quenching evolution of dust, cold gas, and polycyclic aromatic hydrocarbons (PAHs), using flexible star-formation histories and a framework tracking small and large carbonaceous and silicate grains. At $z\sim1$, we find that QGs of similar mass ($M_\star\sim8\times10^{10} M_\odot$), stellar-population age ($\sim2$ Gyr), and cold gas fractions ($f_{\rm gas}\sim1$-$10\%$), span $2$-$3$ dex in $M_{\rm dust}/M_\star$ and $M_{\rm dust}/M_{\rm gas}$, ranging from star-forming-like ratios to highly depleted dust states. The diversity arises from delayed dust injection by thermally pulsing asymptotic giant branch (TP-AGB) stars and ISM grain growth, which sustain dust enrichment for up to $\sim2.5$ Gyr after quenching. Without these channels, the pre-quenching $M_{\rm dust}$ falls below $10\%$ of its initial value within $\lesssim0.5$-$1$ Gyr, and twice as fast when AGN feedback is active. The imprint of post-quenching dust processing persists in substantial reservoirs of small carbonaceous grains, with PAH fractions of $\sim2$-$3\%$, even if the cold-dust budget falls below typical ALMA continuum detection limits ($M_{\rm dust}/M_\star\lesssim10^{-4}$). Such signatures may remain detectable with JWST/MIRI at $μ$Jy depths, probing chemically enriched dust phases in otherwise ALMA-faint galaxies. Altogether, dust and PAHs provide independent probes of distinct stages of ISM evolution in QGs, rather than simply tracing the residual cold ISM of the preceding star-forming phase.

Short digest

Donevski et al. introduce UNDUST, a one-zone semi-analytic model for the coupled post-quenching evolution of cold gas, dust, grain sizes, and PAHs in high-redshift quiescent galaxies. For galaxies with comparable stellar mass, stellar-population age, and cold-gas fraction, the models produce a broad range of dust fractions and dust-to-gas ratios, from star-forming-like values to strongly dust-depleted states. Delayed TP-AGB dust injection and grain growth can maintain enrichment for up to several Gyr after quenching, while AGN-driven heating and outflows accelerate depletion; meanwhile, small carbonaceous grains can preserve appreciable PAH fractions after the cold-dust reservoir becomes ALMA-faint. The paper therefore frames JWST/MIRI PAH emission as a complementary diagnostic of chemically enriched post-quenching ISM phases that dust-continuum surveys may miss.

Key figures to inspect

• Figure 2. This is the core population-level result: it shows how post-quenching dust fraction and dust-to-gas ratio diverge across destruction regimes, with and without AGN feedback, and places the tracks against existing CO and dust-continuum constraints on quiescent galaxies.
• Figure 4. This figure isolates the physical origin of the total dust evolution by separating inherited dust, delayed TP-AGB injection, and ISM grain growth. It directly demonstrates why replenishment channels can prolong dust survival even as the pre-quenching reservoir is being destroyed.
• Figure 7. The PAH-fraction diagnostic connects the model's grain-processing physics to an observable population plane. It shows that PAH-rich small carbonaceous-grain reservoirs can persist through multiple post-quenching stages and respond differently to AGN feedback and destruction strength.
• Figure 8. This is the paper's main observational forecast, translating the PAH evolution into JWST/MIRI fluxes and identifying the regime where quiescent galaxies remain MIRI-detectable after falling below representative ALMA dust-continuum limits.