English (United Kingdom)

https://curated-unify.zendy.io/wp-json/zendy-region/v1/featured_content/oa?rat=en

https://curated-unify.zendy.io/wp-json/zendy-region/v1/highlighted_journal/

Global: Zendy Plus annual

Presents the access of premium content as premium feature

Premium Content

Presents the keyphrase highlighting as premium feature

Keyphrase Highlighting

Presents the summarisation as premium feature

Summarisation

Insights

Presents the pdf analysis as premium feature

PDF Analysis

Presents the zaia usage as premium feature

ZAIA

Global: Zendy Plus monthly

Global: Zendy Tools annual

Global: Zendy Tools monthly

Global: Zendy Free Plan

The reported detection of the global 21-cm signal by the EDGES collaborationis significantly stronger than standard astrophysical predictions. One possibleexplanation is an early radio excess above the cosmic microwave background.Such a radio background could have been produced by high redshift galaxies, ifthey were especially efficient in producing low-frequency synchrotronradiation. We have previously studied the effects of such an inhomogeneousradio background on the 21-cm signal; however, we made a simplifying assumptionof isotropy of the background seen by each hydrogen cloud. Here we perform acomplete calculation that accounts for the fact that the 21-cm absorptionoccurs along the line of sight, and is therefore sensitive to radio sourceslying behind each absorbing cloud. We find that the complete calculationstrongly enhances the 21-cm power spectrum during cosmic dawn, by up to twoorders of magnitude; on the other hand, the effect on the global 21-cm signalis only at the $5\%$ level. In addition to making the high-redshift 21-cmfluctuations potentially more easily observable, the line of sight radio effectinduces a new anisotropy in the 21-cm power spectrum. While these effects areparticularly large for the case of an extremely-enhanced radio efficiency, theymake it more feasible to detect even a moderately-enhanced radio efficiency inearly galaxies. This is especially relevant since the EDGES signal has beencontested by the SARAS experiment.

Strong 21-cm fluctuations and anisotropy due to the line-of-sight effect of radio galaxies at cosmic dawn