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

May 2016 • 2016ApJ...822...29F

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

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\lt z\lt 6.0 (< z> =4.8) in the Cosmic Evolution Survey (COSMOS), for which unique UV spectra from the Deep Imaging Multi-object Spectrograph (DEIMOS) and accurate stellar masses from the Spitzer Large Area Survey with Hyper-Suprime-Cam (SPLASH) are available. The average galaxy population at z∼ 5 and {log}(M/{M})\gt 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 or no Lyα emission to have metallicities comparable to z ∼ 2 galaxies and therefore may represent an evolved subpopulation 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 consistent with observations at z ∼ 2. The relation between stellar mass and metallicity (MZ relation) is similar to z∼ 3.5, but there are indications of it being slightly shallower, in particular for the young, Lyα-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. Because of 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.


IPAC Authors


Andreas Faisst

Assistant Scientist


Elise Furlan

Associate Scientist

Daniel Masters

Assistant Scientist