Detection of the Cosmological 21 cm Signal in Auto-correlation at z ~ 1 with the Canadian Hydrogen Intensity Mapping Experiment

TL;DR

This paper reports the first detection of the cosmological 21 cm auto-correlation signal at redshift around 1 using CHIME, demonstrating the instrument's capability for large-scale structure studies.

Contribution

It presents a novel detection of the 21 cm intensity mapping signal at z ~ 1 with improved data processing and validation methods, establishing CHIME's effectiveness for cosmological measurements.

Findings

Detected 21 cm auto-power spectrum at 12.5 sigma significance.

Measured the signal in two sub-bands with 8.7 and 9.2 sigma significance.

Implemented advanced RFI detection, beamforming, and foreground filtering techniques.

Abstract

We present the first detection of the cosmological 21 cm intensity mapping signal in auto-correlation at z ~ 1 with the Canadian Hydrogen Intensity Mapping Experiment (CHIME). Using 94 nights of observation, we have measured the 21 cm auto-power spectrum over a frequency range from 608.2 MHz to 707.8 MHz (z = 1.34 to 1.01) at 0.4 h Mpc^-1 < k < 1.5 h Mpc^-1, with a detection significance of 12.5 sigma. Our analysis employs significant improvements to the CHIME data processing pipeline compared to previous work, including novel radio frequency interference (RFI) detection and masking algorithms, achromatic beamforming techniques, and foreground filtering before time averaging to minimize spectral leakage. We establish the robustness and reliability of our detection through a comprehensive suite of validation tests. We also measure the 21 cm signal in two independent sub-bands centered at z ~ 1.08 and z ~ 1.24 with detection significance of 8.7 sigma and 9.2 sigma, respectively. We briefly discuss the theoretical interpretation of these measurements in terms of a power spectrum model, deferring the details to a companion paper. This auto-power spectrum detection demonstrates CHIME's capability to probe large-scale structure through 21 cm intensity mapping without reliance on external galaxy surveys.