Impact of Self-shielding Minihalos on the Ly$α$ Forest at High Redshift
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| Format: | Preprint |
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2023
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| _version_ | 1866917694422384640 |
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| author | Park, Hyunbae Lukić, Zarija Sexton, Jean Alvarez, Marcelo Shapiro, Paul R. |
| author_facet | Park, Hyunbae Lukić, Zarija Sexton, Jean Alvarez, Marcelo Shapiro, Paul R. |
| contents | Dense gas in minihalos with masses of $10^6-10^8~M_\odot$ can shield themselves from reionization for $\sim100$ Myr after being exposed to the UV background. These self-shielded systems, often unresolved in cosmological simulations, can introduce strong absorption in quasar spectra. This paper is the first systematic study on the impact of these systems on the Ly$α$ forest. We first derive the HI column density profile of photoevaporating minihalos by conducting 1D radiation-hydrodynamics simulations. We utilize these results to estimate the Ly$α$ opacity from minihalos in a large-scale simulation that cannot resolve self-shielding. When the ionization rate of the background radiation is $0.03\times10^{-12}~{\rm s}^{-1}$, as expected near the end of reionization at $z\sim5.5$, we find that the incidence rate of damped Ly$α$ absorbers increases by a factor of $\sim2-4$ compared to at $z=4.5$. The Ly$α$ flux is, on average, suppressed by $\sim 3\%$ of its mean due to minihalos. The absorption features enhance the 1D power spectrum up to $\sim5\%$ at $k\sim0.1~h~{\rm Mpc}^{-1}~({\rm or}~10^{-3}~{\rm km}^{-1}~{\rm s})$, which is comparable to the enhancement caused by inhomogeneous reionization. The flux is particularly suppressed in the vicinity of large halos along the line-of-sight direction at separations of up to $10~h^{-1}~{\rm Mpc}$ at $r_\perp\lesssim2~h^{-1}~{\rm Mpc}$. However, these effects become much smaller for higher ionizing rates ($\gtrsim0.3\times10^{-12}~{\rm s}^{-1}$) expected in the post-reionization Universe. Our findings highlight the need to consider minihalo absorption when interpreting the Ly$α$ forest at $z\gtrsim5.5$. Moreover, the sensitivity of these quantities to the ionizing background intensity can be exploited to constrain the intensity itself. |
| format | Preprint |
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arxiv_https___arxiv_org_abs_2309_04129 |
| institution | arXiv |
| publishDate | 2023 |
| record_format | arxiv |
| spellingShingle | Impact of Self-shielding Minihalos on the Ly$α$ Forest at High Redshift Park, Hyunbae Lukić, Zarija Sexton, Jean Alvarez, Marcelo Shapiro, Paul R. Cosmology and Nongalactic Astrophysics Dense gas in minihalos with masses of $10^6-10^8~M_\odot$ can shield themselves from reionization for $\sim100$ Myr after being exposed to the UV background. These self-shielded systems, often unresolved in cosmological simulations, can introduce strong absorption in quasar spectra. This paper is the first systematic study on the impact of these systems on the Ly$α$ forest. We first derive the HI column density profile of photoevaporating minihalos by conducting 1D radiation-hydrodynamics simulations. We utilize these results to estimate the Ly$α$ opacity from minihalos in a large-scale simulation that cannot resolve self-shielding. When the ionization rate of the background radiation is $0.03\times10^{-12}~{\rm s}^{-1}$, as expected near the end of reionization at $z\sim5.5$, we find that the incidence rate of damped Ly$α$ absorbers increases by a factor of $\sim2-4$ compared to at $z=4.5$. The Ly$α$ flux is, on average, suppressed by $\sim 3\%$ of its mean due to minihalos. The absorption features enhance the 1D power spectrum up to $\sim5\%$ at $k\sim0.1~h~{\rm Mpc}^{-1}~({\rm or}~10^{-3}~{\rm km}^{-1}~{\rm s})$, which is comparable to the enhancement caused by inhomogeneous reionization. The flux is particularly suppressed in the vicinity of large halos along the line-of-sight direction at separations of up to $10~h^{-1}~{\rm Mpc}$ at $r_\perp\lesssim2~h^{-1}~{\rm Mpc}$. However, these effects become much smaller for higher ionizing rates ($\gtrsim0.3\times10^{-12}~{\rm s}^{-1}$) expected in the post-reionization Universe. Our findings highlight the need to consider minihalo absorption when interpreting the Ly$α$ forest at $z\gtrsim5.5$. Moreover, the sensitivity of these quantities to the ionizing background intensity can be exploited to constrain the intensity itself. |
| title | Impact of Self-shielding Minihalos on the Ly$α$ Forest at High Redshift |
| topic | Cosmology and Nongalactic Astrophysics |
| url | https://arxiv.org/abs/2309.04129 |