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The Impact of Coupled Dark Energy Cosmologies on the High-Redshift Intergalactic Medium

Marco Baldi, Matteo Viel

TL;DR

Problem: whether a coupling between dark energy and dark matter leaves observable imprints on the high-redshift intergalactic medium. Approach: perform high-resolution hydrodynamical simulations with gas cooling and star formation in cDE models and compare Lyman-alpha flux statistics (PDF and power spectrum) to ΛCDM, then constrain the coupling $β$ with an MCMC analysis over cosmological and astrophysical parameters. Findings: coupling induces a scale-dependent enhancement of growth and an underdense skew in the IGM density PDF, leading to 2–10% changes in the flux statistics; combining PDF and flux power yields a robust 2σ upper limit of $β \lesssim 0.15$. Significance: provides a new, independent IGM-based constraint on cDE and highlights the potential of upcoming QSO surveys to tighten bounds.

Abstract

We present an analysis of high-resolution hydrodynamical N-body simulations of coupled dark energy cosmologies which focusses on the statistical properties of the transmitted Lyman-alpha flux in the high-redshift intergalactic medium (IGM). In these models the growth of the diffuse cosmic web differs from the standard LCDM case: the density distribution is skewed towards underdense regions and the matter power spectra are typically larger (in a scale dependent way). These differences are also appreciable in the Lyman-alpha flux and are larger than 5% (10%) at z=2-4 in the flux probability distribution function (pdf) for high transmissivity regions and for values of the coupling parameter β= 0.08 (β= 0.2). The flux power spectrum is also affected at the ~2% (~ 5-10%) level for β= 0.08 (β= 0.2) in a redshift dependent way. We infer the behaviour of flux pdf and flux power for a reasonable range of couplings and present constraints using present high and low resolution data sets. We find an upper limit β< 0.15 (at 2 sigma confidence level), which is obtained using only IGM data and is competitive with those inferred from other large scale structure probes.

The Impact of Coupled Dark Energy Cosmologies on the High-Redshift Intergalactic Medium

TL;DR

Problem: whether a coupling between dark energy and dark matter leaves observable imprints on the high-redshift intergalactic medium. Approach: perform high-resolution hydrodynamical simulations with gas cooling and star formation in cDE models and compare Lyman-alpha flux statistics (PDF and power spectrum) to ΛCDM, then constrain the coupling with an MCMC analysis over cosmological and astrophysical parameters. Findings: coupling induces a scale-dependent enhancement of growth and an underdense skew in the IGM density PDF, leading to 2–10% changes in the flux statistics; combining PDF and flux power yields a robust 2σ upper limit of . Significance: provides a new, independent IGM-based constraint on cDE and highlights the potential of upcoming QSO surveys to tighten bounds.

Abstract

We present an analysis of high-resolution hydrodynamical N-body simulations of coupled dark energy cosmologies which focusses on the statistical properties of the transmitted Lyman-alpha flux in the high-redshift intergalactic medium (IGM). In these models the growth of the diffuse cosmic web differs from the standard LCDM case: the density distribution is skewed towards underdense regions and the matter power spectra are typically larger (in a scale dependent way). These differences are also appreciable in the Lyman-alpha flux and are larger than 5% (10%) at z=2-4 in the flux probability distribution function (pdf) for high transmissivity regions and for values of the coupling parameter β= 0.08 (β= 0.2). The flux power spectrum is also affected at the ~2% (~ 5-10%) level for β= 0.08 (β= 0.2) in a redshift dependent way. We infer the behaviour of flux pdf and flux power for a reasonable range of couplings and present constraints using present high and low resolution data sets. We find an upper limit β< 0.15 (at 2 sigma confidence level), which is obtained using only IGM data and is competitive with those inferred from other large scale structure probes.

Paper Structure

This paper contains 6 sections, 1 equation, 2 figures.

Table of Contents

  1. Introduction
  2. hydrodynamical simulations of coupled dark energy models
  3. Results
  4. Impact on density and flux statistics
  5. Constraints on the coupling
  6. Conclusions

Figures (2)

  • Figure 1: Left: The IGM density pdf of the RP5 (thick curves), and the $\Lambda$CDM (thin curves) models at $z=2.2,3,4.2$ (red dashed, black continuous, blue dotted curves, respectively). Right: Matter power spectra of the $\Lambda$CDM and the RP5 models.
  • Figure 2: Left: Ratio between the flux pdf of the RP5 (thick curves), RP2 (thin curves) and the $\Lambda$CDM models at $z=2.2,3,4.2$ (red dashed, black continuous, blue dotted curves, respectively). Right: Percentage differences between the flux power of the RP2 and RP5 models and that of $\Lambda$CDM. The shaded areas in both panels represent the statistical error at $z=2.94$ for the high resolution PDF data of Kim et al. (2007) and for the $z=3$ bin of the SDSS QSO flux power as computed by McDonald et al. (2006).