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arXiv · 2112.07691

HeII Ly$α$ Transmission Spikes and Absorption Troughs in Eight High-resolution Spectra Probing the End of HeII Reionization

Kirill Makan·Gábor Worseck·Frederick B. Davies·Joseph F. Hennawi·J. Xavier Prochaska·Philipp Richter
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Abstract

We present statistics of HeII Lya transmission spikes and large-scale absorption troughs using archival high-resolution ($R=λ/Δλ\simeq 12,500$-$18,000$) far-UV spectra of eight HeII-transparent quasars obtained with the Cosmic Origins Spectrograph on the Hubble Space Telescope. The sample covers the redshift range 2.5 100cMpc at z>3 to L~30cMpc at z~2.7, signaling a significant progression of HeII reionization at these redshifts. Furthermore, unexpectedly long L~65cMpc troughs detected at z~2.9 suggest that the UV background fluctuates at larger scales than predicted by current models. By comparing the measured incidence of transmission spikes to predictions from forward-modeled mock spectra created from the outputs of a (146cMpc)^3 optically thin Nyx hydrodynamical simulation employing different UV background models, we infer the redshift evolution of the HeII photoionization rate $Γ_\mathrm{He\,II}(z)$. The photoionization rate decreases with increasing redshift from $\simeq 4.6\times 10^{-15}\mathrm{\,s^{-1}}$ at z~2.6 to $\simeq 1.2 \times 10^{-15}\mathrm{\,s^{-1}}$ at z~3.2, in agreement with previous inferences from the HeII effective optical depth, and following expected trends of current models of a fluctuating HeII-ionizing background.

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Kirill Makan, Gábor Worseck, Frederick B. Davies, Joseph F. Hennawi, J. Xavier Prochaska, Philipp Richter. 2022-02-09. HeII Ly$α$ Transmission Spikes and Absorption Troughs in Eight High-resolution Spectra Probing the End of HeII Reionization. https://doi.org/10.3847/1538-4357%2Fac524a

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