Misc,
On the effect of the ionising background on the Ly\alpha forest autocorrelation function
(2014)cite arxiv:1404.7425Comment: 12 pages, 6 figures Accepted for publication in MNRAS.
Abstract
An analytical framework is presented to understand the effects of a
fluctuating intensity of the cosmic ionising background on the correlations of
the Ly\alpha forest transmission fraction measured in quasar spectra. In the
absence of intensity fluctuations, the Ly\alpha power spectrum should have
the expected cold dark matter power spectrum with redshift distortions in the
linear regime, with a bias factor b_\delta and a redshift distortion
parameter \beta that depend on redshift but are independent of scale. The
intensity fluctuations introduce a scale dependence in both b_\delta and
\beta, but keeping their product b_\delta\beta fixed. Observations of the
Ly\alpha correlations and cross-correlations with radiation sources like
those being done at present in the BOSS survey of SDSS-III (Busca et al. 2013;
Slosar et al. 2013; Font-Ribera et al. 2014) have the potential to measure this
scale dependence, which reflects the biasing properties of the sources and
absorbers of the ionising background. We also compute a second term affecting
the Ly\alpha spectrum, due to shot noise in the sources of radiation. This
term is very large if luminous quasars are assumed to produce the ionising
background and to emit isotropically with a constant luminosity, but should be
reduced by a contribution from galaxies, and by the finite lifetime and
anisotropic emission of quasars.
