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Abstract We report the detection of 21 cm emission at an average redshift in the cross-correlation of data from the Canadian Hydrogen Intensity Mapping Experiment (CHIME) with measurements of the Lyαforest from eBOSS. Data collected by CHIME over 88 days in the 400–500 MHz frequency band (1.8 <z< 2.5) are formed into maps of the sky and high-pass delay filtered to suppress the foreground power, corresponding to removing cosmological scales withk∥≲ 0.13 Mpc−1at the average redshift. Line-of-sight spectra to the eBOSS background quasar locations are extracted from the CHIME maps and combined with the Lyαforest flux transmission spectra to estimate the 21 cm–Lyαcross-correlation function. Fitting a simulation-derived template function to this measurement results in a 9σdetection significance. The coherent accumulation of the signal through cross-correlation is sufficient to enable a detection despite excess variance from foreground residuals ∼6–10 times brighter than the expected thermal noise level in the correlation function. These results are the highest-redshift measurement of 21 cm emission to date, and they set the stage for future 21 cm intensity mapping analyses atz> 1.8.
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Cosmological constraints from the eBOSS Lyman-α forest using the PRIYA simulations
Abstract We present new cosmological parameter constraints from the eBOSS Lyman-α forest survey. We use a new theoretical model and likelihood based on the PRIYA simulation suite. PRIYA is the first suite to resolve the Lyman-αforest in a (120 Mpc/h)3volume, using a multi-fidelity emulation technique. We use PRIYA to predict Lyman-αforest observables with ≲ 1% interpolation error over an 11 dimensional (9 simulated, 2 in post-processing) parameter space. We identify an internal tension within the flux power spectrum data. Once the discrepant data is removed, we find the primeval scalar spectral index measured at a pivot scale ofk0= 0.78 Mpc-1to benP= 1.009+0.027-0.018at 68% confidence. This measurement from the Lyman-αforest flux power spectrum alone is in reasonable agreement with Planck, and in tension with earlier eBOSS analyses. The amplitude of matter fluctuations isσ8= 0.733+0.026-0.029at 68% confidence, in agreement with Dark Energy Survey weak lensing measurements and other small-scale structure probes and in tension with CMB measurements from Planck and ACT. The effective optical depth to Lyman-α photons from our pipeline is in good agreement with earlier high resolution measurements. We find a linear power atz= 3 andk= 0.009 s/km of Δ2L= 0.302+0.024-0.027with a slopeneff= -2.264+0.026-0.018. Our flux power spectrum only chains prefer a low level of heating during helium reionization. When we add IGM temperature data we findnP= 0.983 ± 0.020 andσ8= 0.703+0.023-0.027. Our chains prefer an early and long helium reionization event, as suggested by measurements from the helium Lyman-αforest. In the near future we will use our pipeline to infer cosmological parameters from the DESI Lyman-α data.
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- Award ID(s):
- 2215705
- PAR ID:
- 10534750
- Publisher / Repository:
- IOP Publishing
- Date Published:
- Journal Name:
- Journal of Cosmology and Astroparticle Physics
- Volume:
- 2024
- Issue:
- 07
- ISSN:
- 1475-7516
- Page Range / eLocation ID:
- 029
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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- Free Publicly Accessible Full Text
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Accepted Manuscript1.0
- Journal Article:
- https://doi.org/10.1088/1475-7516/2024/07/029
