# First measurement of the Mg II forest correlation function in the Epoch of Reionization

**Authors:** Suk Sien Tie, Joseph F. Hennawi, Feige Wang, Silvia Onorato, Jinyi Yang, Eduardo Bañados, Frederick B. Davies, Jose Oñorbe  
**arXiv:** [2308.11888](https://arxiv.org/abs/2308.11888)  
**Date:** 2023-08-23  
**Summary page:** https://www.summarizepaper.com/en/paper/2308.11888v1/

## Key points

- Researchers aimed to measure the correlation function of the MgII forest transmission in the Epoch of Reionization (EoR)
- EoR is a crucial period when the intergalactic medium (IGM) transitioned from being neutral to ionized
- Previous studies using Lyman-alpha (Lya) transition were ineffective in probing reionization at redshifts greater than 6
- The team focused on strong low-ionization transitions like the MgII doublet to probe reionization
- The researchers measured the auto-correlation of the MgII forest transmission using ten ground-based quasar spectra with redshifts greater than or equal to 6.80
- The correlation function showed strong small-scale clustering and a prominent peak at the doublet velocity, indicating strong absorbers in galaxies' circumgalactic medium (CGM)
- After identifying and masking these absorbers, it was found that what remained was consistent with noise
- They compared their measurements to models generated by combining hydrodynamical simulations with semi-numerical reionization topology, assuming uniform enrichment model
- They obtained an upper limit for [Mg/H] of -3.73 at z_MgII = 6.47 with uninformative priors on [Mg/H] and IGM's neutral fraction x_HI

## Summary

In a recent study, researchers aimed to measure the correlation function of the MgII forest transmission in the Epoch of Reionization (EoR). The EoR is a crucial period when the intergalactic medium (IGM) transitioned from being neutral to ionized. Massive stars explode and release metals into their surroundings during this process. Previous studies using the Lyman-alpha (Lya) transition were ineffective in probing reionization at redshifts greater than 6; therefore, the team focused on strong low-ionization transitions like the MgII doublet. These transitions can give rise to a detectable "metal-line forest" if metals pollute the neutral IGM. The researchers measured the auto-correlation of the MgII forest transmission using ten ground-based quasar spectra with redshifts greater than or equal to 6.80. The spectra spanned a redshift range of 5.96 < z_MgII < 7.42, with a median redshift of z_MgII = 6.47. The correlation function showed strong small-scale clustering and a prominent peak at the doublet velocity (768 km/s), indicating strong absorbers in galaxies' circumgalactic medium (CGM). After identifying and masking these absorbers, it was found that what remained was consistent with noise. To compare their measurements to models generated by combining hydrodynamical simulations with semi-numerical reionization topology, assuming uniform enrichment model, they obtained an upper limit for [Mg/H] of -3.73 at z_MgII = 6.47 with uninformative priors on [Mg/H] and IGM's neutral fraction x_HI.