Good point! It seems that they do not mention metallicity in this paper. However they have spectroscopic redshifts from a previous Hubble Space Telescope (HST)

Good point! It seems that they do not mention metallicity in this paper. However they have spectroscopic redshifts from a previous Hubble Space Telescope (HST) survey [1]. So maybe from that data the metallicity can be estimated. [1] https://iopscience.iop.org/article/10.3847/0067-0049/225/2/27 https://iopscience.iop.org/article/10.3847/0067-0049/225/2/2...