The VANDELS survey: a strong correlation between Ly alpha equivalent width and stellar metallicity at 3 <= z <= 5
Monthly Notices of the Royal Astronomical Society Oxford University Press 495:1 (2020) 1501-1510
Authors:
F Cullen, Rj McLure, Js Dunlop, Ac Carnall, Dj McLeod, Ae Shapley, R Amorin, M Bolzonella, M Castellano, A Cimatti, M Cirasuolo, O Cucciati, A Fontana, F Fontanot, B Garilli, L Guaita, Mj Jarvis, L Pentericci, L Pozzetti, M Talia, G Zamorani, A Calabro, G Cresci, Jpu Fynbo, Np Hathi, M Giavalisco, A Koekemoer, F Mannucci, A Saxena
Abstract:
We present the results of a new study investigating the relationship between observed Ly α equivalent width (Wλ(Ly α)) and the metallicity of the ionizing stellar population (Z★) for a sample of 768 star-forming galaxies at 3 ≤ z ≤ 5 drawn from the VANDELS survey. Dividing our sample into quartiles of rest-frame Wλ(Ly α) across the range −58 Å ≾ Wλ(Ly α) ≾ 110 Å, we determine Z★ from full spectral fitting of composite far-ultraviolet spectra and find a clear anticorrelation between Wλ(Ly α) and Z★. Our results indicate that Z★ decreases by a factor ≳ 3 between the lowest Wλ(Ly α) quartile (≺Wλ(Ly α)≻ = −18 Å) and the highest Wλ(Ly α) quartile (≺Wλ(Ly α)≻ = 24 Å). Similarly, galaxies typically defined as Lyman alpha emitters (LAEs; Wλ(Ly α) > 20 Å) are, on average, metal poor with respect to the non-LAE galaxy population (Wλ(Ly α) ≤ 20 Å) with Z★non-LAE ≳ 2 × Z★LAE. Finally, based on the best-fitting stellar models, we estimate that the increasing strength of the stellar ionizing spectrum towards lower Z★ is responsible for ≈15−25 per cent of the observed variation in Wλ(Ly α) across our sample, with the remaining contribution (≈75−85 per cent) being due to a decrease in the H I/dust covering fractions in low- Z★ galaxies.
