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arXiv · 2103.06300

The NIRVANDELS Survey: a robust detection of $\alpha$-enhancement in star-forming galaxies at $z\simeq3.4$

F. Cullen·A. E. Shapley·R. J. McLure·J. S. Dunlop·R. L. Sanders·M. W. Topping·N. A. Reddy·R. Amorin·R. Begley·M. Bolzonella·A. Calabro·A. C. Carnall·M. Castellano·A. Cimatti·M/ Cirasuolo·G. Cresci·A. Fontana·F. Fontanot·B. Garilli·L. Guaita·M. Hamadouche·N. P. Hathi·F. Mannucci·D. J. McLeod·L. Pentericci·A. Saxena·M. Talia·G. Zamorani
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Abstract

We present results from the NIRVANDELS survey investigating the gas-phase metallicity ($\mathrm{Z}_{\mathrm{gas}}$, tracing O/H) and stellar metallicity ($Z_{\star}$, tracing Fe/H) of 33 star-forming galaxies at redshifts $2.95 < z < 3.80$. Based on a combined analysis of deep optical and near-IR spectra, tracing the rest-frame far ultraviolet and rest-frame optical respectively, we present the first simultaneous determination of the stellar and gas-phase mass-metallicity relationships (MZRs) at $z\simeq3.4$. In both cases, we find that metallicity increases with increasing stellar mass ($M_{\star}$), and that the power-law slope at $M_{\star} \lesssim 10^{10} \mathrm{M}_{\odot}$ 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., $\alpha$-enhancement) at $z>3$, finding $\mathrm{(O/Fe)}\simeq (2.54 \pm 0.38) \times \mathrm{(O/Fe)}_{\odot}$, with no clear dependence on $M_{\star}$.

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F. Cullen, A. E. Shapley, R. J. McLure, J. S. Dunlop, R. L. Sanders, M. W. Topping, N. A. Reddy, R. Amorin, R. Begley, M. Bolzonella, A. Calabro, A. C. Carnall, M. Castellano, A. Cimatti, M/ Cirasuolo, G. Cresci, A. Fontana, F. Fontanot, B. Garilli, L. Guaita, M. Hamadouche, N. P. Hathi, F. Mannucci, D. J. McLeod, L. Pentericci, A. Saxena, M. Talia, G. Zamorani. 2021-03-10. The NIRVANDELS Survey: a robust detection of $\alpha$-enhancement in star-forming galaxies at $z\simeq3.4$. https://doi.org/10.1093/mnras/stab1340

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