#import "importer/main.typ": *
#import "helpers.typ": *

= Conclusion <conclusion>

With the highly anticipated detection of the reionization signal and upcoming observations of the conditions of the IGM during the cosmic dawn, the interpretation of these observations requires accurate predictions from theoretical models and simulations. #beorn
by @Schaeffer_2023
is a semi-numerical simulation framework that implements the halo model of reionization
#cite(<schneider2023cosmologicalforecast21cmpower>, form: "normal") #cite(<Schneider_2021>, form: "normal").
It uses flux profiles to express the emission of radiation by sources in terms of their host halo to efficiently simulate the reionization on large volumes and to generate predictions for the 21-cm signal. It excels in its computational efficiency and flexibility, allowing for fast and flexible execution.

We have presented an extension to #beorn that improves the physical accuracy by implementing a more consistent growth of galaxies based on the individual mass accretion histories of their host dark matter halo. We use the fact that the input data from the underlying #nbody simulation already includes constraints on the growth from the halo properties at different snapshots. Disregarding this information and instead assuming a fixed accretion rate for all halos is an oversimplification. The proof-of-concept implementation presented here leverages the halo history encoded in the merger trees of the #thesan simulation. More broadly, the updated framework is now better suited to incorporate more detailed growth simulations and can be easily extended to other simulations. We also refactored the simulation procedure and achieved a faster execution time by a factor of two. This further enhances the usability of #beorn for large parameter studies.

After validating the new procedure we have shown that the consistent modeling of halo growth produces simulation outputs which have distinct features compared to simpler models. We compared map outputs direcly and also analyzed global quantities and their derived signal. The results are sensitive to the distribution of accretion rates, highlighting the importance of careful modeling of the halo growth.


Works going beyond this proof-of-concept implementation should utilize more sophisticated history tracking that ensures the consistency of halo properties across mutlitple timesteps (e.g. the `rockstar` halo finder by @Behroozi_2012). We also highlighted the limitations incurred by the coarse mass resolution of the #thesan simulation, which is why subsequent research should be based on higher resolution simulations in order to benefit from accurate accretion rate matching down to the lowest halo masses.

Furthermore, our analysis of halo growth shows that a simple modeling relying on the halo mass alone is insufficient. Many of the radiative properties in the halo model of reionization have similarly been expressed as a function of halo mass. Given the increasing evidence against simple mass-only models such as the stellar-to-halo-mass relation, the refinement of these models using stochasticity or additional halo properties is a promising avenue for future research. The impact of revised models, including our refinement to the halo growth will be subject to a future publication.

