Impact of higher spatial resolution on self-regulation and required AGN coupling efficiency

Investigate whether increasing the minimum spatial resolution in the RAMSES zoom-in simulations of massive Cosmic Dawn galaxies from approximately 10 pc to about 1 pc alters the conclusion that achieving observed z>9 supermassive black hole masses requires reducing the AGN thermal coupling efficiency and may prevent self‑regulation by AGN feedback, given that higher resolution can change gas density structure around the sink and the inferred self‑regulated mass.

Background

In comparing their simulations to JWST observations, the authors argue that, at their current minimum cell size (Δx_min ≃ 10 pc) and sink radius (r_sink ≃ 40 pc), matching observed SMBH masses would require reducing the AGN thermal coupling efficiency, which also raises the self‑regulated mass scale of the black hole. They caution, however, that both the cold–hot transition mass and the self‑regulated mass scale depend explicitly on the feedback deposition scale (and thus on resolution), so increasing spatial resolution to ~1 pc could qualitatively change these conclusions by modifying the gas structure (e.g., smoothing scales) around the sink region.

The authors explicitly state that it is unclear whether the same requirement on AGN coupling and the implied prevention of self‑regulation would hold at higher resolution, motivating targeted resolution studies to test the robustness of their self‑regulation picture.

References

It is unclear if this would be true as increasing resolution can have other unforeseen effects (e.g. gas density is smoothed over the resolution scale).

— Supermassive Black Hole Growth in Massive Galaxies at Cosmic Dawn  (2510.19822 - Sunseri et al., 22 Oct 2025) in Section 3.2, 'Comparison to Observations'

The effective thermal coupling factor $\epsilon_r$ assumed in our work also remains uncertain, and therefore should be regarded as a phenomenological parameter rather than a fully predictive quantity.

— The Road to Normalcy: Environment-Driven Evolutionary Pathways for Primordial Black Holes  (2608.23498 - Zhang et al., 24 Aug 2026) in Section 5, Limitations and Caveats