Kavli Affiliate: Nickolay Y. Gnedin
| First 5 Authors: Emily Koivu, Emily Koivu, , ,
| Summary:
Currently the asteroid mass window (mass $sim 10^17- 10^21$ grams)
remains unconstrained for Primordial Black Holes (PBHs) to make up all of the
dark matter content of the universe. Given these PBHs have very small masses,
their Hawking temperature can be up to hundreds of keV. This study investigates
the potential impacts of PBH Hawking radiation on the intergalactic medium from
$zsim 800-25$, namely studying the ionization history, kinetic gas
temperature, and ultimately the 21 cm signature. We find that for masses on the
low edge of the asteroid mass window, there are up two orders of magnitude
increases in the ionization fraction and kinetic gas temperature by redshift
25, and the 21 cm spin temperature can differ from non-PBH cosmology by factors
of a few. This analysis results in maximum differential brightness temperatures
of +17 mK for our lightest PBH masses of $2.12times 10^16$g. We also show
maximal $53$ mK discrepancies in differential brightness temperatures between
our PBH and non-PBH cosmologies for our lightest PBH mass, while our heaviest
PBH mass of $1.65 times 10^17$g shows only $0.5$ mK variations. We find the
Hawking-radiated electrons and positrons are instrumental in driving these IGM
modifications. This study shows the necessity for a rigorous treatment of
Hawking radiation in PBH cosmological observables from the dark ages through
cosmic dawn.
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