Cake Talk by Minami Nakane
We present constraints on hydrogen neutral fraction (xHI) at z=7-13 from clear redshift evolution of Lyα equivalent width (EW) (Nakane et al. 2024a, ApJ, 967, 28). We measure Lyα EWs for 53 galaxies at z=6.6-13.2spectroscopically identified by JWST/NIRSpec multiple programs of ERS, GO, DDT, and GTO. We find clear redshift evolution of Lyα EW, and then estimate xHI by comparing Lyα EW distribution models and our Lyα EW measurements. The moderately large xHI values of xHI<0.79, =062, and 0.93 at z~7, 8, and 9-13, respectively, are consistent with previous studies, and strongly indicate a late reionization history. We also present an O/Fe ratio of GN-z11, a luminous galaxy at z=10.60 with the deep public JWST/NIRSpec data (Nakane et al. 2024b, arXiv e-prints, arXiv:2407.14470). We fit the medium-resolution grating spectra with the stellar model spectra in the rest-frame UV wavelength range with Fe absorption lines, carefully masking out other emission or absorption lines. We obtain low O/Fe ratio of [O/Fe]=-0.39 compared to Milky Way stars and lower redshift galaxies. Because z=10.60 is an early epoch (~430 Myr) after the Big Bang, Fe enrichment is not likely to caused by Type-Ia SNe which require delay time, but by bright hypernovae and/or hypothetical pair instability supernovae. We also confirm the connection between GN-z11and globular cluster formation, which has been pointed out by the high N/O ratios of them, by O/Fe ratio.