Kavli Affiliate: Mark Vogelsberger
| First 5 Authors: Meredith Neyer, Aaron Smith, Rahul Kannan, Mark Vogelsberger, Enrico Garaldi
| Summary:
An important characteristic of cosmic reionization is the growth of ionized
gas bubbles surrounding early luminous objects. Understanding the connections
between the formation and coalescence of these bubbles and their originating
astrophysical sources is equally critical. We present results from a study of
bubble sizes using the state-of-the-art THESAN radiation-hydrodynamics
simulation suite, which self-consistently models radiation transport and
realistic galaxy formation. We employ the mean-free path method, and track the
evolution of the effective ionized bubble size at each point ($R_{rm eff}$)
throughout the Epoch of Reionization. We show there is a slow growth period for
regions ionized early, but a rapid flash ionization process for regions ionized
later as they immediately enter a large, pre-existing bubble. We also find that
bright sources are preferentially in larger bubbles, and find consistency with
recent observational constraints at $z gtrsim 9$, but tension with idealized
Lyman-alpha damping-wing models at $z approx 7$ when the size distribution is
complex. We find that high overdensity regions have larger characteristic
bubble sizes, but the correlation decreases as reionization progresses, likely
due to the runaway formation of large percolated bubbles. Finally, we compare
the redshift at which a region transitions from neutral to ionized ($z_{rm
reion}$) with the time it takes to reach a given bubble size and conclude that
$z_{rm reion}$ is a reasonable local probe of small-scale bubble size
statistics ($R_text{eff} lesssim 1$ cMpc). However, for larger bubbles, the
correspondence between $z_{rm reion}$ and size statistics weakens due to the
time delay between the onset of reionization and the expansion of a large
bubble, particularly at high redshifts.
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