The ALPINE-CRISTAL-JWST Survey: Chemical Abundance Comparison between the ISM and CGM of Main-sequence Galaxies at <i>z</i>  = 4–6

Abstract Gaseous halos around galaxies play an important role in galaxy evolution. The exchange of metals from the interstellar medium (ISM) to the circumgalactic medium (CGM) is caused by the formation, feedback, and/or merging history of galaxies. We study the variation in chemical composition between the ISM (≲3 kpc) and CGM (∼5–10 kpc) for a sample of M ⋆ &gt; 10 9.5 M ⊙ main-sequence galaxies at 4 &lt; z &lt; 6 with both JWST and Atacama Large Millimeter/submillimeter Array observations. Using JWST/NIRSpec integral field spectroscopy, we derive the optical line ratios from the ISM and the CGM for our sample, focusing on the typical optical lines used for metallicity studies. Our comparison shows that the ISM and the CGM have similar chemical abundances. This indicates that the CGM of these typical 4 &lt; z &lt; 6 galaxies is enriched to the level of their ISM in the early Universe. Using statistical tests, we find that some of the line ratios show marginal differences between the ISM and CGM. Combined with Cloudy modeling, our results suggest that a difference in ionization level (higher for the ISM) is the dominant reason for the observed ratio difference of oxygen line ratios. There is also indication of a deficit in the nitrogen abundance with respect to oxygen in the CGM, which suggests a delay in redistribution of secondary nitrogen. Finally, an enhanced F [C II]158 μ m / F H α ratio is observed in the CGM, suggesting that feedback and/or mergers play a key role in metal mixing.