Kavli Affiliate: George Efstathiou
| First 5 Authors: Harry T. J. Bevins, Stefan Heimersheim, Irene Abril-Cabezas, Anastasia Fialkov, Eloy de Lera Acedo
| Summary:
The first billion years of cosmic history remains largely unobserved. We
demonstrate, using a novel machine learning technique, how combining upper
limits on the spatial fluctuations in the 21-cm signal with observations of the
sky-averaged 21-cm signal from neutral hydrogen can improve our understanding
of this epoch. By jointly analysing data from SARAS3 (redshift $zapprox15-25$)
and limits from HERA ($zapprox8$ and $10$), we show that such a synergetic
analysis provides tighter constraints on the astrophysics of galaxies 200
million years after the Big Bang than can be achieved with the individual data
sets. Although our constraints are weak, this is the first time data from a
sky-averaged 21-cm experiment and power spectrum experiment have been analysed
together. In synergy, the two experiments leave only $64.9^{+0.3}_{-0.1}$% of
the explored broad theoretical parameter space to be consistent with the joint
data set, in comparison to $92.3^{+0.3}_{-0.1}$% for SARAS3 and
$79.0^{+0.5}_{-0.2}$% for HERA alone. We use the joint analysis to constrain
star formation efficiency, minimum halo mass for star formation, X-ray
luminosity of early emitters and the radio luminosity of early galaxies. The
joint analysis disfavours at 68% confidence a combination of galaxies with
X-ray emission that is $lesssim 33$ and radio emission that is $gtrsim 32$
times as efficient as present day galaxies. We disfavour at $95$% confidence
scenarios in which power spectra are $geq126$ mK$^{2}$ at $z=25$ and the
sky-averaged signals are $leq-277$ mK.
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