The VANDELS survey: The relation between the UV continuum slope and stellar metallicity in star-forming galaxies at z ∼ 3

¹ INAF – Osservatorio Astronomico di Roma, Via di Frascati 33, 00078 Monte Porzio Catone, Italy
e-mail: antonello.calabro@inaf.it
² INAF – Astronomical Observatory of Trieste, Via G.B. Tiepolo 11, 34143 Trieste, Italy
³ IFPU – Institute for Fundamental Physics of the Universe, Via Beirut 2, 34151 Trieste, Italy
⁴ SUPA, Institute for Astronomy, University of Edinburgh, Royal Observatory, Edinburgh EH9 3HJ, UK
⁵ INAF – Osservatorio Astronomico di Bologna, Via P. Gobetti 93/3, 40129 Bologna, Italy
⁶ University of Bologna, Department of Physics and Astronomy (DIFA), Via Gobetti 93/2, 40129 Bologna, Italy
⁷ Instituto de Investigación Multidisciplinar en Ciencia y Tecnología, Universidad de La Serena, Raúl Bitrán 1305, La Serena, Chile
⁸ Departamento de Física y Astronomía, Universidad de La Serena, Av. Juan Cisternas 1200 Norte, La Serena, Chile
⁹ INAF – Osservatorio Astrofisico di Arcetri, Largo E. Fermi 5, 50125 Firenze, Italy
¹⁰ Cosmic DAWN Center, Niels Bohr Institute, University of Copenhagen, Juliane Maries Vej 30, 2100 Copenhagen Ø, Denmark
¹¹ Centre for Astrophysics Research, University of Hertfordshire, Hatfield AL10 9AB, UK
¹² Space Telescope Science Institute, 3700 San Martin Drive, Baltimore, MD 21218, USA
¹³ European Southern Observatory (ESO), Vitacura, Chile
¹⁴ DARK, Niels Bohr Institute, University of Copenhagen, Lyngbyvej 2, 2100 Copenhagen, Denmark
¹⁵ Department of Physics and Astronomy, University College London, Gower Street, London WC1E 6BT, UK
¹⁶ Observatoire de Genève, Université de Genève, 51 Ch. des Maillettes, 1290 Versoix, Switzerland
¹⁷ CNRS, IRAP, 14 avenue E. Belin, 31400 Toulouse, France
¹⁸ Tianjin Astrophysics Center, Tianjin Normal University, Binshuixidao 393, 300384 Tianjin, PR China

Received: 24 August 2020
Accepted: 12 November 2020

Abstract

The estimate of stellar metallicities (Z_*) of high-z galaxies are of paramount importance in order to understand the complexity of dust effects and the reciprocal interrelations among stellar mass, dust attenuation, stellar age, and metallicity. Benefiting from uniquely deep far-UV spectra of > 500 star-forming galaxies at redshifts 2 <  z <  5 extracted from the VANDELS survey and stacked in bins of stellar mass (M_*) and UV continuum slope (β), we estimate their stellar metallicities Z_* from stellar photospheric absorption features at 1501 and 1719 Å, which are calibrated with Starburst99 models and are largely unaffected by stellar age, dust, IMF, nebular continuum, or interstellar absorption. Comparing them to photometric-based spectral slopes in the 1250–1750 Å range, we find that the stellar metallicity increases by ∼0.5 dex from β ∼ −2 to β ∼ −1 (1 ≲ A₁₆₀₀ ≲ 3.2), and a dependence with β holds at fixed UV absolute luminosity M_UV and stellar mass up to ∼10^9.65 M_⊙. As a result, metallicity is a fundamental ingredient for properly rescaling dust corrections based on M_UV and M_*. Using the same absorption features, we analyzed the mass-metallicity relation (MZR), and find it to be consistent with the previous VANDELS estimation based on a global fit of the FUV spectra. Similarly, we do not find a significant evolution between z ∼ 2 and z ∼ 3.5. Finally, the slopes of our MZR and Z_* − β relation are in agreement with the predictions of well-studied semi-analytic models (SAM) of galaxy formation, while some tensions remain concerning the absolute metallicity normalization. The relation between the UV slope and stellar metallicity is fundamental to the exploitation of large volume surveys with next-generation telescopes and for the physical characterization of galaxies in the first billion years of our Universe.