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We present the results of near-infrared spectroscopic observations for a sample of 12 star-forming galaxies at 1.01 DEEP2 galaxies in our sample are significantly offset from the excitation sequence observed in nearby HII regions and SDSS emission-line galaxies. This offset implies that physical conditions are different in the HII regions of distant galaxies hosting intense star formation, and may affect the chemical abundances derived from strong-line ratios for such objects (Abridged).
Shapley et al. (Thu,) studied this question.