A measurement of the Ly β forest power spectrum and its cross with the Ly α forest in X-Shooter XQ-100
Abstract
The Ly α forest is the large-scale structure probe for which we appear to have modelling control to the highest wavenumbers. This makes the Ly α forest of great interest for constraining the warmness/fuzziness of dark matter and the timing of reionization processes. However, the standard statistic, the Ly α forest power spectrum, is unable to strongly constrain the intergalactic medium (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 Ly β forest and its cross-correlation with the coeval Ly α forest using the 100 spectra of z = 3.5-4.5 quasars in the VLT/X-Shooter XQ-100 Legacy Survey, motivated by the Ly β transition's smaller absorption cross-section that makes it sensitive to somewhat higher densities relative to the Ly α transition. Our inferences from this measurement for the IGM temperature-density relation appear to latch consistently on to the recent tight lower redshift Ly α forest constraints. The z = 3.4-4.7 trends we find using the Ly α-Ly β cross-correlation show a flattening of the slope of the temperature-density relation with decreasing redshift. This is the trend anticipated from ongoing He II 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 Ly α forest, with the cross-correlation being immune to systematics that are uncorrelated between the two forests, such as metal line contamination.
- Publication:
-
Monthly Notices of the Royal Astronomical Society
- Pub Date:
- January 2022
- DOI:
- 10.1093/mnras/stab3017
- arXiv:
- arXiv:2106.04837
- Bibcode:
- 2022MNRAS.509.2423W
- Keywords:
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- intergalactic medium;
- Astrophysics - Cosmology and Nongalactic Astrophysics
- E-Print:
- doi:10.1093/mnras/stab3017