  Spatial fluctuations in ultraviolet backgrounds can subtly modulate the
distribution of extragalactic sources, a potential signal and systematic for
large-scale structure surveys. While this modulation has been shown to be
significant for 3D Ly alpha forest surveys, its relevance for other large-scale
structure probes has been hardly explored, despite being the only astrophysical
process that likely can affect clustering measurements on the scales of >~Mpc.
We estimate that the background fluctuations, modulating the amount of H I,
have a fractional effect of (0.03-0.3) x (k/[10^-2 Mpc^-1])^-1 on the power
spectrum of 21 cm intensity maps at z = 1-3. We find a smaller effect for H
alpha and Ly alpha intensity mapping surveys of (0.001-0.1) x (k/[10^-2
Mpc^-1])-1 and even smaller effect for more traditional surveys that correlate
the positions of individual H alpha or Ly alpha emitters. We also estimate the
effect of backgrounds on low-redshift galaxy surveys in general based on a
simple model in which background fluctuations modulate the rate halo gas cools,
modulating star formation: We estimate a maximum fractional effect on the power
of ~0.01 (k/[10-2 Mpc-1])-1 at z = 1. We compare sizes of these imprints to
cosmological parameter benchmarks for the next generation of redshift surveys:
We find that ionizing backgrounds could result in a bias on the squeezed
triangle non-Gaussianity parameter fNL that can be larger than unity for power
spectrum measurements with a SPHEREx-like galaxy survey, and typical values of
intensity bias. Marginalizing over a shape of the form k-1PL, where PL is the
linear matter power spectrum, removes much of this bias at the cost of ~ 40%
larger statistical errors.
