The NIRVANDELS Survey: a robust detection of α-enhancement in star-forming galaxies at <i>z</i> ≃ 3.4
Fergus Cullen, Alice E. Shapley, R. J. McLure, J. S. Dunlop, Ryan L. Sanders, Michael W. Topping, Naveen A. Reddy, R. Amorín, R Begley, M. Bolzonella, Antonello Calabrò, Adam C. Carnall, M. Castellano, A. Cimatti, M. Cirasuolo, G. Cresci, A. Fontana, Fabio Fontanot, B. Garilli, L. Guaita, M. L. Hamadouche, Nimish P. Hathi, F. Mannucci, D J McLeod, L. Pentericci, Aayush Saxena, M. Talia, G. Zamorani
Abstract
ABSTRACT We present results from the NIRVANDELS survey on the gas-phase metallicity (Zg, tracing O/H) and stellar metallicity (Z⋆, tracing Fe/H) of 33 star-forming galaxies at redshifts 2.95 &lt; z &lt; 3.80. Based on a combined analysis of deep optical and near-IR spectra, tracing the rest-frame far-ultraviolet (FUV; 1200–2000 Å) and rest-frame optical (3400–5500 Å), respectively, we present the first simultaneous determination of the stellar and gas-phase mass–metallicity relationships (MZRs) at z ≃ 3.4. In both cases, we find that metallicity increases with increasing stellar mass (M⋆) and that the power-law slope at M⋆ ≲ 1010M⊙ of both MZRs scales as $Z \propto M_{\star }^{0.3}$. Comparing the stellar and gas-phase MZRs, we present direct evidence for super-solar O/Fe ratios (i.e. α-enhancement) at z &gt; 3, finding (O/Fe) = 2.54 ± 0.38 × (O/Fe)⊙, with no clear dependence on M⋆.