We present the first results from MARTA (Measuring Abundances at high Redshift with the Te Approach), a programme that leverages ultra-deep, medium-resolution JWST/NIRSpec spectroscopy to probe the interstellar medium of star-forming galaxies at z ∼ 2−3. We report detections of one or more auroral lines, including O iii λ4363, O ii λλ7320, 7330, S ii λ4068, and S iii λ6312, 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 redshifts 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, and 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 due to low-number statistics. Finally, we leveraged our sample together with a comprehensive compilation of galaxies with O iii λ4363 detections from the literature to recalibrate classical strong-line diagnostics at high redshifts. 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).
E. et al. (Wed,) studied this question.