Inferring the IGM thermal history during reionisation with the
Lyman-$\alpha$ forest power spectrum at redshift $z 5$
(2016)cite arxiv:1605.04155Comment: 13 pages, 6 figures, 2 Tables, submitted to MNRAS.Abstract
We use cosmological hydrodynamical simulations to assess the feasibility of
constraining the thermal history of the intergalactic medium during
reionisation with the Ly$\alpha$ forest at $z 5$. Pressure smoothing has
a measurable impact on the transmitted flux power spectrum that can be isolated
from Doppler broadening at this redshift. We parameterise the effect of
pressure smoothing on the power spectrum using the cumulative energy per
proton, $u_0$, deposited into a gas parcel at the mean background density, a
quantity that is tightly linked with the integrated thermal history and the gas
density power spectrum in the simulations. We construct mock observations of
the line of sight Ly$\alpha$ forest power spectrum and use a Markov Chain Monte
Carlo approach to recover $u_0$ at redshifts $5 z 12$. A
statistical uncertainty of $20$ per cent is expected (at 68 per cent
confidence) at $z5$ using high resolution spectra with a total redshift
path length of $\Delta z=4$ and a typical signal-to-noise ratio of $S/N=15$
per pixel. Estimates for the expected systematic uncertainties are comparable,
such that existing data should enable a measurement of $u_0$ to within $\sim
30$ per cent. This translates to distinguishing between reionisation scenarios
with similar instantaneous temperatures at $z5$, but with an energy
deposited per proton that differs by $2$--$3\, eV$ over the redshift
interval $5z 12$. For an initial temperature of $T10^4\rm\,K$
following reionisation, this corresponds to the difference between early
($z_re=12$) and late ($z_re=7$) reionisation in our models.
Description
[1605.04155] Inferring the IGM thermal history during reionisation with the Lyman-$\alpha$ forest power spectrum at redshift $z \simeq 5$