We present the first results from MARTA (Measuring Abundances at high Redshift with the Tₑ Approach), a programme leveraging ultra-deep, medium-resolution JWST/NIRSpec spectroscopy to probe the interstellar medium (ISM) of star-forming galaxies at z 2 - 3. We report detections of one or more auroral lines, including O III4363, O IIλ7320, 7330, S II 4068, and S III 6312 for 16 galaxies in the sample, providing measurements of multiple ionic temperatures. We tested the validity of the TO II-TO III relation at high redshift considering a total sample of 21 objects including literature data, and obtained a shallower slope than in the low-z literature. However, such a slope is consistent with low-redshift data when ultra-low metallicity objects are considered. We assessed the correlation of the TO II-TO III relationship and its scatter on different physical parameters, finding a mild correlation with the ionisation parameter and radiation field hardness, while no significant correlation with gas density. The location of high-redshift data is also consistent with the low-z literature in the TO II-TS II, and TS III-TO III relations, although this conclusion is limited with low-number statistics. Finally, we leveraged our sample together with a comprehensive compilation of galaxies with O III4363 detections from the literature to recalibrate classical strong-line diagnostics at high redshift. MARTA represents a key addition in this space because it provides direct metallicities at moderately high oxygen abundances (12+log (O/H) 8. 0-8. 4).
Cataldi et al. (Fri,) studied this question.