2024/05/01 by T. M. Stanton, Fergus Cullen, Stanton, T. M. +39 · 5 citations
Physics and Astronomy · #Astronomy and Astrophysical Research #Galaxies: Formation, Evolution, Phenomena #Stellar, planetary, and galactic studies
paper · pdf · doi:10.48550/arxiv.2405.00774
We present determinations of the gas-phase and stellar metallicities of a sample of 65 star-forming galaxies at z ≃ 3.5 using rest-frame far-ultraviolet (FUV) spectroscopy from the VANDELS survey in combination with follow-up rest-frame optical spectroscopy from VLT/KMOS and Keck/MOSFIRE. We infer gas-phase oxygen abundances (Zg; tracing O/H) via strong optical nebular lines and stellar iron abundances (Z⋆; tracing Fe/H) from full spectral fitting to the FUV continuum. Our sample spans the stellar mass range 8.5 < log(M⋆/M\odot) < 10.5 and shows clear evidence for both a stellar and gas-phase mass-metallicity relation (MZR). We find that our O and Fe abundance estimates both exhibit a similar mass-dependence, such that Fe/H∝ M⋆0.30±0.11 and O/H∝ M⋆0.32±0.09. At fixed M⋆ we find that, relative to their solar values, O abundances are systematically larger than Fe abundances (i.e., α-enhancement).We estimate an average enhancement of (O/Fe) = 2.65 ± 0.16 × (O/Fe)_\odot which appears to be independent of M⋆. We employ analytic chemical evolution models to place a constraint on the strength of galactic-level outflows via the mass-outflow factor (η). We show that outflow efficiencies that scale as η∝ M⋆-0.32 can simultaneously explain the functional form of of the stellar and gas-phase MZR, as well as the degree of α-enhancement at fixed Fe/H. Our results add further evidence to support a picture in which α-enhanced abundance ratios are ubiquitous in high-redshift star-forming galaxies, as expected for young systems whose interstellar medium is primarily enriched by core-collapse supernovae.