Abstract Contamination-free assessments of the interstellar medium and star formation in quasar host galaxies, particularly in the far-infrared, offer insights into the role of supermassive black holes in galaxy evolution. Motivated by simulations of quasar-heated dust on nuclear and galaxy-wide scales, we perform two-component (host galaxy + point source) modeling of high-resolution (∼0.1″) ALMA observations of the continuum in Band 5 (λrest∼500 μm) of three luminous quasars (Lbol ∼ 1047 erg s−1) at z = 2. For two quasars, we include Band 9 (λrest∼154 μm; 0.06″ and 0.3″) data, which further constrains the unresolved nuclear component. To break the degeneracy between quasar and stellar heating of dust on extended scales, we use CO (J=5–4) to gauge the expected contribution of star formation to the infrared luminosity. We find very good agreement, between the strength and spatial distribution of the extended continuum and its prediction from CO (J=5-4). This is supported by our three quasars following along the LCO(5 − 4) − LIR, SFR relation for inactive star-forming galaxies. As a consequence, there is no evidence for extended continuum emission that could be attributed to quasar-heated dust. As expected, the nuclear (i.e., torus) contribution is present and subdominant (e.g., 12% in Band 9 for one quasar with a typical star-forming host) or non-existent (8% in Band 9 for the starburst). Substantial levels of star formation agree with previous estimates from unresolved ALMA observations, which find SFRs consistent with star-forming main-sequence galaxies. Therefore, our results do not provide evidence for quasar-mode feedback, even in the most luminous cases.
Silverman et al. (2026) studied this question.