Kavli Affiliate: Nickolay Y. Gnedin
| First 5 Authors: Hanjue Zhu, Nickolay Y. Gnedin, , ,
| Summary:
We investigate the properties of cosmological ionization fronts during the
Epoch of Reionization using the CROC simulations. By analyzing reionization
timing maps, we characterize ionization front velocities and curvatures and
their dependence on the density structure of the intergalactic medium (IGM).
The velocity distribution of ionization fronts in the simulations indicates
that while the barrier-crossing analytical model captures the overall shape in
high-velocity regions, it fails to reproduce the low-velocity tail,
highlighting the non-Gaussian nature of the IGM’s density field. Ionization
front velocities are inversely correlated with local density, propagating
faster in underdense regions and more slowly in overdense environments. Faster
ionization fronts also lead to higher post-ionization temperatures, reaching a
plateau at $sim 2 times 10^4$ K for velocities exceeding 3000 km/s. Examining
curvature statistics further establishes a connection between ionization front
structure and the normalized density contrast $nu$, with trends in overdense
regions aligning well with barrier-crossing model predictions, while deviations
appear in underdense environments due to model limitations. These results
provide a detailed characterization of ionization front dynamics and their
interaction with the underlying density field, bridging small-scale
reionization physics with large-scale observables such as the 21 cm signal and
the IGM’s thermal history.
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