Beamforming approaches towards detecting the 21-cm global signal from Cosmic Dawn with radio array telescopes
Abstract
The formation of the first stars and galaxies during `Cosmic Dawn' is thought to have imparted a faint signal onto the 21-cm spin temperature from atomic Hydrogen gas in the early Universe. Observationally, an absorption feature should be measurable as a frequency dependence in the sky-averaged (i.e. global) temperature at meter wavelengths. This signal should be separable from the smooth—but orders of magnitude brighter—foregrounds by jointly fitting a log-polynomial and absorption trough to radiometer spectra. A majority of approaches to measure the global 21-cm signal use radiometer systems on dipole-like antennas. Here, we argue that beamforming-based methods may allow radio arrays to measure the global 21-cm signal. We simulate an end-to-end drift-scan observation of the radio sky at 50-100 MHz using a zenith-phased array, and find that the complex sidelobe structure introduces a significant frequency-dependent systematic. However, the $λ/D$ evolution of the beam width with frequency does not confound detection. We conclude that a beamformed array with a median sidelobe level ${∼}-50$ dB may offer an alternative method to measure the global 21-cm signal. This level is achievable by arrays with $O(10^5)$ antennas.
- Publication:
-
Publications of the Astronomical Society of Australia
- Pub Date:
- November 2022
- DOI:
- 10.1017/pasa.2022.54
- arXiv:
- arXiv:2210.04693
- Bibcode:
- 2022PASA...39...60P
- Keywords:
-
- astronomical instrumentation: radio telescopes;
- astronomical techniques: time domain astronomy;
- radio frequency interference;
- Astrophysics - Instrumentation and Methods for Astrophysics;
- Astrophysics - Cosmology and Nongalactic Astrophysics
- E-Print:
- Accepted to PASA