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 redshifted 21 cm transition line of hydrogen tracks the thermal evolutionof the neutral intergalactic medium (IGM) at "cosmic dawn," during theemergence of the first luminous astrophysical objects (~100 Myr after the BigBang) but before these objects ionized the IGM (~400-800 Myr after the BigBang). Because X-rays, in particular, are likely to be the chief energy courierfor heating the IGM, measurements of the 21 cm signature can be used to inferknowledge about the first astrophysical X-ray sources. Using analytic argumentsand a numerical population synthesis algorithm, we argue that the progenitorsof supermassive black holes (SMBHs) should be the dominant source of hardastrophysical X-rays---and thus the primary driver of IGM heating and the 21 cmsignature---at redshifts $z < 20$, if (i) they grow readily from the remnantsof Population III stars and (ii) produce X-rays in quantities comparable towhat is observed from active galactic nuclei and high-mass X-ray binaries. Weshow that models satisfying these assumptions dominate over contributions toIGM heating from stellar populations, and cause the 21 cm brightnesstemperature to rise at $z > 20$. An absence of such a signature in theforthcoming observational data would imply that SMBH formation occurred later(e.g. via so-called direct collapse scenarios), that it was not a commonoccurrence in early galaxies and protogalaxies, or that it produced far fewerX-rays than empirical trends at lower redshifts, either due to intrinsicdimness (radiative inefficiency) or Compton-thick obscuration close to thesource.

The imprint of the cosmic supermassive black hole growth history on the 21 cm background radiation