The intergalactic medium transmission towards z ≳ 4 galaxies with VANDELS and the impact of dust attenuation^⋆

¹ European Southern Observatory, Av. Alonso de Córdova 3107, Vitacura, Santiago, Chile
e-mail: rthomas@eso.org
² INAF, Osservatorio Astronomico di Roma, Via Frascati 33, 00078 Monteporzio Catone, Italy
³ Aix Marseille Université, CNRS, LAM (Laboratoire d’Astrophysique de Marseille), UMR 7326, 13388 Marseille, France
⁴ INAF – Osservatorio di Astrofisica e Scienza dello Spazio di Bologna, Via Gobetti 93/3, 40129 Bologna, Italy
⁵ Observatoire de Genève, Université de Genève, 51 Ch. des Maillettes, 1290 Versoix, Switzerland
⁶ Instituto de Investigación Multidisciplinar en Ciencia y Tecnología, Universidad de La Serena, Raúl Bitrán 1305 La Serena, Chile
⁷ Departamento de Física y Astronomía, Universidad de La Serena, Norte, Av. Juan Cisternas 1200, La Serena, Chile
⁸ SUPA, Institute for Astronomy, University of Edinburgh, Royal Observatory, Edinburgh EH9 3HJ, UK
⁹ INAF-Astronomical Observatory of Trieste, Via G.B.Tiepolo 11, 34143 Trieste, Italy
¹⁰ Department of Astronomy, The University of Texas at Austin, Austin, TX 78712, USA
¹¹ Instituto de Astrofísica, Universidad Católica de Chile, Vicuña Mackenna 4860, Santiago, Chile
¹² Space Telescope Science Institute, 3700 San Martin Drive, Baltimore, MD 21218, USA
¹³ The Cosmic Dawn Center, Niels Bohr Institute, Copenhagen University, Juliane Maries Vej 30, 2100 Copenhagen, Denmark
¹⁴ University of Bologna, Department of Physics and Astronomy (DIFA), Via Gobetti 93/2, I-40129 Bologna, Italy

Received: 20 May 2019
Accepted: 26 November 2019

Abstract

Aims. Our aim is to estimate the intergalactic medium (IGM) transmission towards UV-selected star-forming galaxies at z ≳ 4 and study the effect of the dust attenuation on these measurements.

Methods. The UV spectrum of high-redshift galaxies is a combination of their intrinsic emission and the effect of the IGM absorption along their line of sight. Using data coming from the unprecedentedly deep spectroscopy from the VANDELS ESO public survey carried out with the VIMOS instrument, we compute both the dust extinction and the mean transmission of the IGM as well as its scatter from a set of 281 galaxies at z >  3.87. Because of a degeneracy between the dust content of the galaxy and the IGM, we first estimate the stellar dust extinction parameter E(B − V) and study the result as a function of the dust prescription. Using these measurements as constraint for the spectral fit we estimate the IGM transmission Tr(Lyα). Both photometric and spectroscopic spectral energy distribution fits are performed using the SPectroscopy And photometRy fiTting tool for Astronomical aNalysis which is able to fit the spectral continuum of the galaxies as well as photometric data.

Results. Using the classical Calzetti attenuation law we find that E(B − V) goes from 0.11 at z = 3.99 to 0.08 at z = 5.15. These results are in very close agreement with published measurements. We estimate the IGM transmission and find that the transmission is decreasing with increasing redshift from Tr(Lyα) = 0.53 at z = 3.99 to 0.28 at z = 5.15. We also find a large standard deviation around the average transmission that is more than 0.1 at every redshift. Our results are in very good agreement with both previous measurements from AGN studies and with theoretical models.