# On the detection of a cosmic dawn signal in the radio background

**Authors:** Saurabh Singh, Jishnu Nambissan T., Ravi Subrahmanyan, N. Udaya Shankar, B. S. Girish, A. Raghunathan, R. Somashekar, K. S. Srivani, Mayuri Sathyanarayana Rao  
**arXiv:** [2112.06778](https://arxiv.org/abs/2112.06778)  
**Date:** 2021-12-13  
**Summary page:** https://www.summarizepaper.com/en/paper/2112.06778v1/

## Key points

- The astrophysics of cosmic dawn marks the beginning of star formation in the first collapsed objects
- Spectral and spatial signatures in the cosmic radio background at long wavelengths are expected during this period
- Studying cosmic dawn through the sky-averaged redshifted 21-cm absorption line of neutral hydrogen provides insights into various aspects such as evolving thermal state of gas, radiation background, Lyman-$\alpha$ radiation from stars interacting with cold primordial gas, and relative populations of hyperfine spin levels in neutral hydrogen atoms
- Singh et al. conducted a radiometer measurement to investigate a profile previously identified by Bowman et al., but their findings revealed that this profile was not of astrophysical origin and was rejected with 95.3% confidence
- Speculation about non-standard cosmology or additional mechanisms for cooling baryons arose due to the significantly higher amplitude of the profile detected by Bowman et al. compared to standard cosmological models
- Singh et al.'s non-detection aligns with earlier concerns and suggests that this profile does not provide evidence for new astrophysics or non-standard cosmology
- Rigorous scrutiny and validation are crucial when interpreting signals from cosmic dawn, emphasizing the ongoing quest to unravel mysteries surrounding this critical phase in our universe's history

## Summary

The astrophysics of cosmic dawn marks the beginning of star formation in the first collapsed objects. This period is expected to leave spectral and spatial signatures in the cosmic radio background at long wavelengths. One crucial aspect of studying cosmic dawn is through the sky-averaged redshifted 21-cm absorption line of neutral hydrogen. This provides insights into the evolving thermal state of gas, radiation background, Lyman-$\alpha$ radiation from stars interacting with cold primordial gas, and relative populations of hyperfine spin levels in neutral hydrogen atoms. Recently, Singh et al. conducted a radiometer measurement of the radio sky spectrum in the 55--85~MHz band to investigate a profile previously identified by Bowman et al. using data from the Experiment to Detect the Global Epoch of Reionization Signature (EDGES) low-band instrument. However, their findings revealed that this profile was not of astrophysical origin and was rejected with 95.3% confidence. The amplitude of the profile detected by Bowman et al. was significantly higher than what standard cosmological models predicted, leading to speculation about non-standard cosmology or additional mechanisms for cooling baryons such as interactions with millicharged dark matter or an excess radio background at redshifts beyond 17. However, Singh et al. 's non-detection aligns with earlier concerns and suggests that this profile does not provide evidence for new astrophysics or non-standard cosmology. This refined analysis highlights the importance of rigorous scrutiny and validation when interpreting signals from cosmic dawn and emphasizes the ongoing quest to unravel the mysteries surrounding this critical phase in our universe's history.