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Large 21 cm signals from AGN-dominated reionization

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Kulkarni, G 
Choudhury, TR 
Puchwein, E 
Haehnelt, MG 


We present predictions for the spatial distribution of 21-cm brightness temperature fluctuations from high-dynamic-range simulations for active galactic nucleus (AGN)-dominated reionization histories that have been tested against available Lyα and cosmic microwave background (CMB) data. We model AGNs by extrapolating the observed Mbh − σ relation to high redshifts and assign them ionizing emissivities consistent with recent UV luminosity function measurements. We assess the observability of the predicted spatial 21-cm fluctuations in the late stages of reionization in the limit in which the hydrogen 21-cm spin temperature is significantly larger than the CMB temperature. Our AGN-dominated reionization histories increase the variance of the 21-cm emission by a factor of up to 10 compared to similar reionization histories dominated by faint galaxies, to values close to 100 mK2 at scales accessible to experiments (k 1 cMpc−1 h). This is lower than the sensitivity reached by ongoing experiments only by a factor of about 2 or less. When reionization is dominated by AGNs, the 21-cm power spectrum is enhanced on all scales due to the enhanced bias of the clustering of the more massive haloes and the peak in the large scale 21-cm power is strongly enhanced and moved to larger scales due to bigger characteristic bubble sizes. AGN-dominated reionization should be easily detectable by Low Frequency Array (and later Hydrogen Epoch of Reionization Array and Phase 1 of the Square Kilometre Array) at their design sensitivity, assuming successful foreground subtraction and instrument calibration. Conversely, these could become the first non-trivial reionization scenarios to be ruled out by 21-cm experiments, thereby constraining the contribution of AGNs to reionization.



galaxies: active, galaxies: high-redshift, intergalactic medium, quasars: general, dark ages, reionization, first stars

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Monthly Notices of the Royal Astronomical Society

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Oxford University Press
Science and Technology Facilities Council (ST/J005673/1)
Science and Technology Facilities Council (ST/K00333X/1)
Science and Technology Facilities Council (ST/N000927/1)
Science and Technology Facilities Council (ST/M007065/1)
Science and Technology Facilities Council (ST/P000673/1)
Science and Technology Facilities Council (ST/L000636/1)
STFC (ST/M007073/1)
Science and Technology Facilities Council (ST/P002315/1)
Science and Technology Facilities Council (ST/R002452/1)
European Research Council (320596)
Support by ERC Advanced grant 320596 ‘The Emergence of Structure During the Epoch of Reionization’ is gratefully acknowledged. EP gratefully acknowledges support by the Kavli Foundation. We acknowledge PRACE for awarding us access to the Curie supercomputer, based in France at the Tres Grand Centre de Calcul ´ (TGCC). This work used the DiRAC Data Centric system at Durham University, operated by the Institute for Computational Cosmology on behalf of the STFC DiRAC HPC Facility ( This equipment was funded by BIS National E-infrastructure capital grant ST/K00042X/1, STFC capital grants ST/H008519/1 and ST/K00087X/1, STFC DiRAC Operations grant ST/K003267/1 and Durham University. DiRAC is part of the National E-Infrastructure. This research was supported by the Munich Institute for Astro- and Particle Physics (MIAPP) of the DFG cluster of excellence ‘Origin and Structure of the Universe’.