Abstract
In preparation for the IGM tomography study by Subaru Prime Focus
Spectrograph (PFS) survey and other large future telescopes such as
TMT/ELT/GMT, we present the results of our pilot study on Lyman-$\alpha$ forest
and IGM tomography statistics using the GADGET3-Osaka cosmological smoothed
particle hydrodynamical simulation. Our simulation includes models for star
formation and supernova feedback, which enables more realistic
cross-correlation studies between galaxies, neutral hydrogen (HI) and metals in
circumgalactic and intergalactic medium. We create light-cone data set at
$z=2-3$ from our simulations and generate mock Ly$\alpha$ forest data. As a
first step, in this paper, we focus on the distribution of HI and galaxies, and
present statistical results on 1-D flux PDF, 1-D power spectrum, flux contrast
vs. impact parameter, HI$-$galaxy cross-correlations. Our results show overall
agreement with current observational data, with some interesting discrepancies
on small scales which are due to either feedback effects or varying
observational conditions. Our simulation shows stronger HI absorption with
decreasing transverse distance from galaxies. Comparison with observations
shows that the current observed data points include important contributions
from lower mass galaxies of $M_10^8-10^10\,M_ødot$ rather
than just from massive galaxies of $M_10^10\,M_ødot$, which
dilutes the stronger signal of flux contrast around massive galaxies. On large
scales, the average absorption decrement smoothly connects to the IGM level,
supporting the concordance $Łambda$ cold dark matter model. We also find an
increase in the HI absorption towards the center of proto-cluster.
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