Misc,
A New Precision Measurement of the Small-Scale Line-of-Sight Power Spectrum of the Ly\alpha Forest
(2017)cite arxiv:1709.07354Comment: 24 pages, 12 figures, submitted to ApJ, machine readable tables will be made available after publication in the journal.
Abstract
We present a new measurement of the Ly\alpha forest power spectrum at $1.8
< z < 3.4$ using 74 Keck/HIRES and VLT/UVES high-resolution, high-S/N quasar
spectra. We developed a custom pipeline to measure the power spectrum and its
uncertainty, which fully accounts for finite resolution and noise, and corrects
for the bias induced by masking missing data, DLAs, and metal absorption lines.
Our measurement results in unprecedented precision on the small-scale modes $k
> 0.02\,s\,km^-1$, unaccessible to previous SDSS/BOSS analyses. It
is well known that these high-$k$ modes are highly sensitive to the thermal
state of the intergalactic medium, however contamination by narrow metal lines
is a significant concern. We quantify the effect of metals on the small-scale
power, and find a modest effect on modes with $k < 0.1\,s\,km^-1 $.
As a result, by masking metals and restricting to $k <
0.1\,s\,km^-1$ their impact is completely mitigated. We present an
end-to-end Bayesian forward modeling framework whereby mock spectra with the
same noise, resolution, and masking as our data are generated from Ly\alpha
forest simulations. These mocks are used to build a custom emulator, enabling
us to interpolate between a sparse grid of models and perform MCMC fits. Our
results agree well with BOSS on scales $k < 0.02\,s\,km^-1$ where
the measurements overlap. The combination of BOSS' percent level low-$k$
precision with our $5-15\%$ high-$k$ measurements, results in a powerful new
dataset for precisely constraining the thermal history of the intergalactic
medium, cosmological parameters, and the nature of dark matter. The power
spectra and their covariance matrices are provided as electronic tables.
