A measurement of the Lyman-beta forest power spectrum and its cross with the Lyman-alpha forest in X-Shooter XQ-100

Abstract

The Lyman-alpha forest is the large-scale structure probe for which we appear to have modeling control to the highest wavenumbers. This makes the Lyman-alpha forest of great interest for constraining the warmness/fuzziness of dark matter and the timing of reionization processes. However, the standard statistic, the Lyman-alpha forest power spectrum, is unable to strongly constrain the IGM temperature-density relation, and this inability further limits how well other high wavenumber-sensitive parameters can be constrained. With the aim of breaking these degeneracies, we measure the power spectrum of the Lyman-beta forest and its cross correlation with the coeval Lyman-alpha forest using the one hundred spectra of z=3.5-4.5 quasars in the VLT/X-Shooter XQ-100 Legacy Survey, motivated by the Lyman-beta transition's smaller absorption cross section that makes it sensitive to somewhat higher densities relative to the Lyman-alpha transition. Our inferences from this measurement for the IGM temperature-density relation appear to latch consistently onto the recent tight lower-redshift Lyman-alpha forest constraints. The z=3.4-4.7 trends we find using the Lyman-alpha$-$Lyman-beta cross correlation show a flattening of the slope of the temperature-density relation with decreasing redshift. This is the trend anticipated from ongoing HeII reionization and there being sufficient time to reach the asymptotic temperature-density slope after hydrogen reionization completes. Furthermore, our measurements provide a consistency check on IGM models that explain the Lyman-alpha forest, with the cross correlation being immune to systematics that are uncorrelated between the two forests, such as metal line contamination.

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Cited by in corpus (8)

• Unveiling Dark Matter free-streaming at the smallest scales with high redshift Lyman-alpha forest
• The 3D Lyman-$\alpha$ Forest Power Spectrum from eBOSS DR16
• The ACCEL2 Project: Precision Measurements of EFT Parameters and BAO Peak Shifts for the Lyman-$\alpha$ Forest
• Probing the cosmic web in Ly$\alpha$ emission over large scales: an Intensity Mapping forecast for DECaLS/BASS and DESI
• The Compressed 3D Lyman-Alpha Forest Bispectrum
• Weighing Cosmic Structures with Clusters of Galaxies and the Intergalactic Medium
• Modeling the Cosmological Lyman-$\alpha$ Forest at the Field Level
• Bridging Simulations and EFT: A Hybrid Model of the Lyman-Alpha Forest Field