Bibcode
Finkelstein, Steven L.; D’Aloisio, Anson; Paardekooper, Jan-Pieter; Ryan, Russell, Jr.; Behroozi, Peter; Finlator, Kristian; Livermore, Rachael; Upton Sanderbeck, Phoebe R.; Dalla Vecchia, Claudio; Khochfar, Sadegh
Bibliographical reference
The Astrophysical Journal, Volume 879, Issue 1, article id. 36, 34 pp. (2019).
Advertised on:
7
2019
Journal
Citations
280
Refereed citations
238
Description
We explore scenarios for reionizing the intergalactic medium with low
galaxy ionizing photon escape fractions. We combine simulation-based
halo mass–dependent escape fractions with an extrapolation of the
observed galaxy rest-ultraviolet luminosity functions to solve for the
reionization history from z = 20\to 4. We explore the posterior
distributions for key unknown quantities, including the limiting halo
mass for star formation, the ionizing photon production efficiency, and
a potential contribution from active galactic nuclei (AGNs). We
marginalize over the allowable parameter space using a Markov chain
Monte Carlo method, finding a solution that satisfies the most
model-independent constraints on reionization. Our fiducial model can
match observational constraints with an average escape fraction of
<5% throughout the bulk of the epoch of reionization if (i) galaxies
form stars down to the atomic cooling limit before reionization and a
photosuppression mass of log(M h/M ⊙) ∼ 9
during/after reionization (‑13 < M UV,lim <‑11), (ii) galaxies become more efficient producers of ionizing
photons at higher redshifts and fainter magnitudes, and (iii) there is a
significant but subdominant contribution by AGNs at z ≲ 7. In this
model, the faintest galaxies (M UV >‑15) dominate
the ionizing emissivity, leading to an earlier start to reionization and
a smoother evolution of the ionized volume-filling fraction than models
that assume a single escape fraction at all redshifts and luminosities.
The ionizing emissivity from this model is consistent with observations
at z = 4–5 (and below, when extrapolated), in contrast to some
models that assume a single escape fraction. Our predicted ionized
volume-filling fraction at z = 7 of {Q}{{{H}}II}}
= 78% (±8%) is in modest (∼1σ–2σ) tension
with observations of Lyα emitters at z ∼ 7 and the
damping-wing analyses of the two known z > 7 quasars, which prefer
{Q}{{{H}}II},z=7} ∼ 40%–50%.
Related projects
Numerical Astrophysics: Galaxy Formation and Evolution
How galaxies formed and evolved through cosmic time is one of the key questions of modern astronomy and astrophysics. Cosmological time- and length-scales are so large that the evolution of individual galaxies cannot be directly observed. Only through numerical simulations can one follow the emergence of cosmic structures within the current
Claudio
Dalla Vecchia