Speaker
Description
The highly redshifted 21 cm emission line from neutral hydrogen has the potential to reveal the temperature, density, and ionization fraction of the IGM during the Cosmic Dawn, when the first stars and galaxies illuminated the universe. The Long Wavelength Array at the Owens Valley Radio Observatory (OVRO-LWA) is currently undergoing an upgrade that substantially improves its sensitivity to this cosmological signal at redshifts z ≈ 16-100. We describe progress upgrading the array and developing a precision analysis pipeline to deep limits on the 21 cm power spectrum from the Cosmic Dawn.
The current upgrade to the OVRO-LWA is the instrument’s second major upgrade, bringing it into “Stage III” of operation. Eastwood et al. 2019 used data from the array’s previous Stage II to produce an upper limit on the 21 cm at z ≈ 18.4. However, due to systematic limitations, that result does not meaningfully constrain cosmological models. We discuss three aspects of the instrument upgrade that will improve 21 cm power spectrum results:
1. The upgrade adds an additional 64 fiber-fed outrigger antennas for a total of 352 antennas. The new antennas extend the array’s longest baseline to 2.4 km and will improve imaging resolution and precision calibration.
2. The overhauled analog signal processing and digital backend improves channel isolation, significantly reducing instrumental cross-talk. Additionally, the upgraded signal path reduces signal reflections and a produces a smoother bandpass response.
3. The adoption of state-of-the-art calibration and power spectrum estimation techniques improves foreground isolation and 21 cm sensitivity.
Commissioning of the OVRO-LWA Stage III is currently underway. The expanded array, improved signal processing, and refined analysis techniques will enable 21 cm power spectrum analyses to produce improved constraints on the Cosmic Dawn.
