# The 21 cm Power Spectrum from the Cosmic Dawn: First Results from the OVRO-LWA

## TL;DR

This paper reports initial results from the OVRO-LWA, setting upper limits on the 21cm power spectrum during cosmic dawn, demonstrating novel foreground filtering techniques, and analyzing systematic errors affecting measurements.

## Contribution

It introduces the first application of the double Karhunen-Loève transform for foreground filtering in 21cm cosmology and provides an updated model of foreground emission.

## Key findings

- Placed upper limits on the 21cm power spectrum at z≈18.4
- Demonstrated the first use of double Karhunen-Loève transform for foreground filtering
- Diagnosed systematic errors limiting current measurements

## Abstract

The 21\,cm transition of neutral hydrogen is opening an observational window into the cosmic dawn of the universe---the epoch of first star formation. We use 28\,hr of data from the Owens Valley Radio Observatory Long Wavelength Array (OVRO-LWA) to place upper limits on the spatial power spectrum of 21\,cm emission at $z \approx 18.4$ ($\Delta_{21} \lesssim 10^4\,\text{mK}$), and within the absorption feature reported by the EDGES experiment (Bowman et al. 2018). In the process we demonstrate the first application of the double Karhunen-Lo\`{e}ve transform for foreground filtering, and diagnose the systematic errors that are currently limiting the measurement. We also provide an updated model for the angular power spectrum of low-frequency foreground emission measured from the northern hemisphere, which can be used to refine sensitivity forecasts for next-generation experiments.