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arXiv · 2312.06747

Possible Contamination of the Intergalactic Medium Damping Wing in ULAS J1342+0928 by Proximate Damped Ly$\alpha$ Absorption

Frederick B. Davies·Eduardo Bañados·Joseph F. Hennawi·Sarah E. I. Bosman
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Abstract

The red damping wing from neutral hydrogen in the intergalactic medium is a smoking-gun signal of ongoing reionization. One potential contaminant of the intergalactic damping wing signal is dense gas associated with foreground galaxies, which can give rise to proximate damped Ly$\alpha$ absorbers. The Ly$\alpha$ imprint of such absorbers on background quasars is indistinguishable from the intergalactic medium within the uncertainty of the intrinsic quasar continuum, and their abundance at $z\gtrsim7$ is unknown. Here we show that the complex of low-ionization metal absorption systems recently discovered by deep JWST/NIRSpec observations in the foreground of the $z=7.54$ quasar ULAS~J1342$+$0928 can potentially reproduce the quasar's spectral profile close to rest-frame Ly$\alpha$ without invoking a substantial contribution from the intergalactic medium, but only if the absorbing gas is extremely metal-poor ($[{\rm O}/{\rm H}]\sim-3.5$). Such a low oxygen abundance has never been observed in a damped Ly$\alpha$ absorber at any redshift, but this possibility still complicates the interpretation of the spectrum. Our analysis highlights the need for deep spectroscopy of high-redshift quasars with JWST or ELT to "purify" damping wing quasar samples, an exercise which is impossible for much fainter objects like galaxies.

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Frederick B. Davies, Eduardo Bañados, Joseph F. Hennawi, Sarah E. I. Bosman. 2023-12-11. Possible Contamination of the Intergalactic Medium Damping Wing in ULAS J1342+0928 by Proximate Damped Ly$\alpha$ Absorption. https://arxiv.org/abs/2312.06747

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