Minami Nakane, Masami Ouchi

We investigate UV absorption lines tracing cool gas in eight bright ($-21.9<M_\mathrm{UV}<-20.5$) galaxies at $z=7.2-10.6$ using deep JWST/NIRSpec medium-resolution spectra homogeneously selected from archival data. We identify multiple absorption lines of low-ionization species (LIS) in five galaxies, while the remaining three show only one or no significant detections. The average LIS equivalent widths $\mathrm{EW_{LIS}}$ indicate weaker absorption lines in compact ($r_\mathrm{e}\lesssim 100$ pc) galaxies with high $L_\mathrm{Hβ}/L_\mathrm{UV}$ and $Σ_\mathrm{SFR}$, suggestive of absorption-line suppression due to intense star formation or nuclear activity. We simultaneously fit multiple LIS lines, accounting for both covering fraction $C_f$ and column density $N$, and find that the five galaxies follow the local $C_f$-$N$ relation. Through the LIS-line fitting, we derive chemical abundance ratios. The five galaxies have abundance ratios similar to those of damped Ly$α$ (DLA) systems in the [Si/O]-[C/O] and [Fe/Si]-[Al/Si] planes, suggesting that their absorbing gas is similar to that of DLAs. We find that two galaxies at $z\sim 7$ are already highly Fe-enriched, with $\mathrm{[Fe/Si]}\simeq -0.2$, near the solar abundance ratio. While the high Fe enrichment may originate from early Type-Ia supernovae (SNe Ia) or pair-instability supernovae (PISNe), these two galaxies also show $\mathrm{[Al/Si]}\sim0$, with no signature of the strong odd-even effect expected from PISNe, favoring SNe Ia.