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.

Links

• SIMBAD http://simbad.u-strasbg.fr/simbo.pl?bibcode=2016ApJ...822...29F
• PDF https://iopscience.iop.org/article/10.3847/0004-637X/822/1/29/pdf
• PDF https://stacks.iop.org/0004-637X/822/29/pdf
• PREPRINT http://arxiv.org/abs/1512.00018
• DATA https://irsa.ipac.caltech.edu/bibdata/2016/F/2016ApJ...822...29F.html
• ELECTR https://doi.org/10.3847%2F0004-637X%2F822%2F1%2F29