Dust thermalization temperature and CMB anisotropy impact from massive ETG formation

Determine the precise thermalization temperature of dust in massive early-type galaxies during their rapid formation at high redshift (approximately 15–20) and quantify how the resulting dust-processed radiation impacts the observed cosmic microwave background anisotropies after redshifting to the present epoch.

Background

The paper argues that massive early-type galaxies formed very rapidly and with top-heavy galaxy-wide initial mass functions at redshifts around 15–20, producing extremely high bolometric luminosities. Given rapid chemical enrichment and dust formation, the authors posit that this radiation would have been efficiently thermalized by dust, yielding a photon field that could contribute significantly to today’s CMB energy density after cosmological redshift.

While the authors provide order-of-magnitude estimates (e.g., effective dust temperatures near 50 K under fiducial assumptions), they explicitly leave the precise determination of the dust thermalization temperature and its quantitative effect on CMB anisotropies for future work. Resolving these quantities is essential to assess whether early massive ETG formation constitutes a significant foreground component that biases CMB analyses.

References

Details such as the precise thermalization temperature of the dust and the impact on CMB anisotropies are left for future works.

— The Impact of Early Massive Galaxy Formation on the Cosmic Microwave Background  (2505.04687 - Gjergo et al., 7 May 2025) in Section 2.3.3 (Thermal equilibrium of the ETG luminosity with cosmic dust emission)

An important question to address is if the forming elliptical galaxies might be directly detectable with, for example the ALMA facility, remembering to take into account that the redshift--time--distance relations will differ for the correct model of cosmology compared to the currently used SMoC relations.

— The relevance of the cosmic microwave background for cosmology  (2609.10672 - Kroupa et al., 9 Sep 2026) in Section 4.5, “Conclusion to Sec. 4: Lesson III”