The NIRVANDELS Survey: a robust detection of α-enhancement in star-forming galaxies at z ≃ 3.4
Monthly Notices of the Royal Astronomical Society(2021)
摘要
We present results from the NIRVANDELS survey on the gas-phase metallicity (Z
g
, tracing O/H) and stellar metallicity (Z
⋆
, 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 (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
⋆
≲ 10
10
M
⊙
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 > 3, finding (O/Fe) = 2.54 ± 0.38 × (O/Fe)
⊙
, with no clear dependence on M
⋆
.
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关键词
galaxies: abundances,galaxies: high redshift
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