Damping Wing-Like Features in the Spectra of High Redshift Quasars: a Challenge for Fully-Coupled Simulations
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2025
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| author | Gnedin, Nickolay Y. Zhu, Hanjue |
| author_facet | Gnedin, Nickolay Y. Zhu, Hanjue |
| contents | Recently, several observational detections of damping-wing-like features at the edges of ``dark gaps" in the spectra of distant quasars (the ``Malloy-Lidz effect") have been reported, rendering strong support for the existence of ``neutral islands" in the universe at redshifts as low as $z<5.5$. We apply the procedure from one of these works, Zhu et al (2024), to the outputs of fully coupled cosmological simulations from two recent large projects, ``Cosmic Reionization On Computers" (CROC) and ``Thesan". Synthetic spectra in both simulations have statistics of dark gaps similar to observations, but do not exhibit the damping wing features. Moreover, a toy model with neutral islands added ``by hand" only reproduces the observational results when the fraction of neutral islands among all dark gaps approaches 90%. I.e., simulations and observations appear to produce two distinct ``populations" of dark gaps. In addition, in the simulations, the neutral islands at $z=5.9$ should be short-lived and should not extend to $z<5.5$. A possible explanation for this discrepancy is that both simulations underestimate the fluctuations in the photoionization rate and, hence, miss a population of long-lived neutral islands, located in the large downward fluctuations of the photoionization rate. |
| format | Preprint |
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arxiv_https___arxiv_org_abs_2504_11539 |
| institution | arXiv |
| publishDate | 2025 |
| record_format | arxiv |
| spellingShingle | Damping Wing-Like Features in the Spectra of High Redshift Quasars: a Challenge for Fully-Coupled Simulations Gnedin, Nickolay Y. Zhu, Hanjue Cosmology and Nongalactic Astrophysics Recently, several observational detections of damping-wing-like features at the edges of ``dark gaps" in the spectra of distant quasars (the ``Malloy-Lidz effect") have been reported, rendering strong support for the existence of ``neutral islands" in the universe at redshifts as low as $z<5.5$. We apply the procedure from one of these works, Zhu et al (2024), to the outputs of fully coupled cosmological simulations from two recent large projects, ``Cosmic Reionization On Computers" (CROC) and ``Thesan". Synthetic spectra in both simulations have statistics of dark gaps similar to observations, but do not exhibit the damping wing features. Moreover, a toy model with neutral islands added ``by hand" only reproduces the observational results when the fraction of neutral islands among all dark gaps approaches 90%. I.e., simulations and observations appear to produce two distinct ``populations" of dark gaps. In addition, in the simulations, the neutral islands at $z=5.9$ should be short-lived and should not extend to $z<5.5$. A possible explanation for this discrepancy is that both simulations underestimate the fluctuations in the photoionization rate and, hence, miss a population of long-lived neutral islands, located in the large downward fluctuations of the photoionization rate. |
| title | Damping Wing-Like Features in the Spectra of High Redshift Quasars: a Challenge for Fully-Coupled Simulations |
| topic | Cosmology and Nongalactic Astrophysics |
| url | https://arxiv.org/abs/2504.11539 |