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Estimates for the impact of Ultraviolet Background fluctuations on galaxy clustering measurements

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Original languageEnglish
Pages (from-to)5059-5072
Number of pages14
JournalMonthly Notices of the Royal Astronomical Society
Issue number4
Early online date14 Mar 2019
Publication statusPublished - 1 Jun 2019


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 Lyα 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 scales ≳Mpc. We estimate that background fluctuations, modulating the amount of H I, have a fractional effect of (0.03 - 0.3) × (k/[10-2Mpc-1])-1 on the power spectrum of 21cm intensity maps at z = 1 - 3. We find a smaller effect for Hα and Lyα intensity mapping surveys of (0.001 - 0.1) × (k/[10-2Mpc-1])-1 and even smaller effect for more traditional surveys that correlate the positions of individual Hα or Lyα 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/[10-2Mpc-1])-1 at z = 1. We compare sizes of these imprints to cosmological parameter benchmarks for the next generation of redshift surveys: We find 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.

    Research areas

  • cosmology: theory, large-scale structure of universe

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