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arXiv · 1512.00018

Rest-UV Absorption Lines as Metallicity Estimator: the Metal Content of Star-Forming Galaxies at z~5

A. L. Faisst·P. L. Capak·I. Davidzon·M. Salvato·C. Laigle·O. Ilbert·M. Onodera·G. Hasinger·Y. Kakazu·D. Masters·B. Mobasher·D. Sanders·J. D. Silverman·L. Yan·N. Z. Scoville
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Abstract

We measure a relation between the depth of four prominent rest-UV absorption complexes and metallicity for local galaxies and verify it up to z~3. We then apply this relation to a sample of 224 galaxies at 3.5 < z < 6.0 ( = 4.8) in COSMOS, for which unique UV spectra from DEIMOS and accurate stellar masses from SPLASH are available. The average galaxy population at z~5 and log(M/Msun) > 9 is characterized by 0.3-0.4 dex (in units of 12+log(O/H)) lower metallicities than at z~2, but comparable to z~3.5. We find galaxies with weak/no Ly-alpha emission to have metallicities comparable to z~2 galaxies and therefore may represent an evolved sub-population of z~5 galaxies. We find a correlation between metallicity and dust in good agreement with local galaxies and an inverse trend between metallicity and star-formation rate (SFR) consistent with observations at z~2. The relation between stellar mass and metallicity (MZ relation) is similar to z~3.5, however, there are indications of it being slightly shallower, in particular for the young, Ly-alpha emitting galaxies. We show that, within a "bathtub" approach, a shallower MZ relation is expected in the case of a fast (exponential) build-up of stellar mass with an e-folding time of 100-200 Myr. Due to this fast evolution, the process of dust production and metal enrichment as a function of mass could be more stochastic in the first billion years of galaxy formation compared to later times.

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A. L. Faisst, P. L. Capak, I. Davidzon, M. Salvato, C. Laigle, O. Ilbert, M. Onodera, G. Hasinger, Y. Kakazu, D. Masters, B. Mobasher, D. Sanders, J. D. Silverman, L. Yan, N. Z. Scoville. 2015-11-30. Rest-UV Absorption Lines as Metallicity Estimator: the Metal Content of Star-Forming Galaxies at z~5. https://doi.org/10.3847/0004-637x%2F822%2F1%2F29

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