The VANDELS survey: A strong correlation between Ly$\alpha$ equivalent width and stellar metallicity at $\mathbf{3\leq z \leq 5}$

Autor: Cullen, F., McLure, R. J., Dunlop, J. S., Carnall, A. C., McLeod, D. J., Shapley, A. E., Amorín, R., Bolzonella, M., Castellano, M., Cimatti, A., Cirasuolo, M., Cucciati, O., Fontana, A., Fontanot, F., Garilli, B., Guaita, L., Jarvis, M. J., Pentericci, L., Pozzetti, L., Talia, M., Zamorani, G., Calabrò, A., Cresci, G., Fynbo, J. P. U., Hathi, N. P., Giavalisco, M., Koekemoer, A., Mannucci, F., Saxena, A.
Rok vydání: 2020
Předmět:
Druh dokumentu: Working Paper
DOI: 10.1093/mnras/staa1260
Popis: We present the results of a new study investigating the relationship between observed Ly$\alpha$ equivalent width ($W_{\lambda}$(Ly$\alpha$)) and the metallicity of the ionizing stellar population ($Z_{\star}$) for a sample of $768$ star-forming galaxies at $3 \leq z \leq 5$ drawn from the VANDELS survey. Dividing our sample into quartiles of rest-frame $W_{\lambda}$(Ly$\alpha$) across the range $-58 \unicode{xC5} \lesssim$ $W_{\lambda}$(Ly$\alpha$) $\lesssim 110 \unicode{xC5}$ we determine $Z_{\star}$ from full spectral fitting of composite far-ultraviolet (FUV) spectra and find a clear anti-correlation between $W_{\lambda}$(Ly$\alpha$) and $Z_{\star}$. Our results indicate that $Z_{\star}$ decreases by a factor $\gtrsim 3$ between the lowest $W_{\lambda}$(Ly$\alpha$) quartile ($\langle$$W_{\lambda}$(Ly$\alpha$)$\rangle=-18\unicode{xC5}$) and the highest $W_{\lambda}$(Ly$\alpha$) quartile ($\langle$$W_{\lambda}$(Ly$\alpha$)$\rangle=24\unicode{xC5}$). Similarly, galaxies typically defined as Lyman Alpha Emitters (LAEs; $W_{\lambda}$(Ly$\alpha$) $>20\unicode{xC5}$) are, on average, metal poor with respect to the non-LAE galaxy population ($W_{\lambda}$(Ly$\alpha$) $\leq20\unicode{xC5}$) with $Z_{\star}$$_{\rm{non-LAE}}\gtrsim 2 \times$ $Z_{\star}$$_{\rm{LAE}}$. Finally, based on the best-fitting stellar models, we estimate that the increasing strength of the stellar ionizing spectrum towards lower $Z_{\star}$ is responsible for $\simeq 15-25\%$ of the observed variation in $W_{\lambda}$(Ly$\alpha$) across our sample, with the remaining contribution ($\simeq 75-85\%$) being due to a decrease in the HI/dust covering fractions in low $Z_{\star}$ galaxies.
Comment: 10 pages, 6 figures, MNRAS accepted
Databáze: arXiv
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