Near-infrared spectroscopic indices for unresolved stellar populations – II. Index measurements

ABSTRACT We measured the equivalent width of a large set near-infrared (NIR, 0.8–2.4$\ \mu$m) line-strength indices in XShooter medium-resolution spectra central regions 14 galaxies. found that two aluminum indices, Al at 1.31 μm and Al1 1.67 μm, CO CO1 1.56 CO4 1.64 are tightly correlated with velocity dispersion. Moreover, NIR show strong correlations optical Mg2 Mgb which usually adopted as α/Fe-enhancement diagnostics. The molecular FeH1 index 1.58 correlates 〈Fe〉 [MgFe]′ used total metallicity Paβ 1.28 has behaviour similar to Hβ index, is diagnostic mean age. defined new composite 〈Al〉 [AlFeH], possible candidates be diagnostics α/Fe enhancement. correlation while [AlFeH] indices. distribution data points Paβ–〈Al〉 Paβ–[AlFeH] diagrams mimics [MgFe]′–Hβ Mgb–〈Fe〉 diagrams, widely constrain properties unresolved stellar populations. concluded some could useful studying populations well fine-tuning population models.