Faint end of the z ∼ 3–7 luminosity function of Lyman-alpha emitters behind lensing clusters observed with MUSE^⋆

¹ Institut de Recherche en Astrophysique et Planétologie (IRAP), Université de Toulouse, CNRS, UPS, CNES, 14 avenue Edouard Belin, 31400 Toulouse, France
e-mail: gdelavieuvil@irap.omp.eu
² Univ. Lyon, Univ. Lyon1, ENS de Lyon, CNRS, Centre de Recherche Astrophysique de Lyon UMR5574, 69230 Saint-Genis-Laval, France
³ Max Planck Institute für Astronomie, Königstuhl 17, 69117 Heidelberg, Germany
⁴ Department of Astronomy, Stockholm University, AlbaNova University Centre, 106 91 Stockholm, Sweden
⁵ Instituto de Astrofísica, Facultad de Física, Pontificia Universidad Católica de Chile, Casilla 306, Santiago 22, Chile
⁶ Space Science Institute, 4750 Walnut Street, Suite 205, Boulder, CO 80301, USA
⁷ Millenium Institute of Astrophysics, Santiago, Chile
⁸ Department of Physics and Astronomy, University College London, Gower Street, London WC1E 6BT, UK
⁹ Dark Cosmology Centre, Niels Bohr Institute, University of Copenhagen, Juliane Maries Vej 30, 2100 Copenhagen, Denmark
¹⁰ Leibniz-Institut für Astrophysik Potsdam (AIP), An der Sternwarte 16, 14482 Potsdam, Germany
¹¹ Leiden Observatory, Leiden University, PO Box 9513, 2300 RA Leiden, The Netherlands
¹² Observatoire de Genève, Université de Genève, 51 Ch. des Maillettes, 1290 Versoix, Switzerland
¹³ Department of Physics, ETH Zurich, Wolfgang–Pauli–Strasse 27, 8093 Zurich, Switzerland

Received: 19 October 2018
Accepted: 29 May 2019

Abstract

Contact. This paper presents the results obtained with the Multi-Unit Spectroscopic Explorer (MUSE) at the ESO Very Large Telescope on the faint end of the Lyman-alpha luminosity function (LF) based on deep observations of four lensing clusters. The goal of our project is to set strong constraints on the relative contribution of the Lyman-alpha emitter (LAE) population to cosmic reionization.

Aims. The precise aim of the present study is to further constrain the abundance of LAEs by taking advantage of the magnification provided by lensing clusters to build a blindly selected sample of galaxies which is less biased than current blank field samples in redshift and luminosity. By construction, this sample of LAEs is complementary to those built from deep blank fields, whether observed by MUSE or by other facilities, and makes it possible to determine the shape of the LF at fainter levels, as well as its evolution with redshift.

Methods. We selected a sample of 156 LAEs with redshifts between 2.9 ≤ z ≤ 6.7 and magnification-corrected luminosities in the range 39 ≲ log L_Lyα [erg s⁻¹] ≲43. To properly take into account the individual differences in detection conditions between the LAEs when computing the LF, including lensing configurations, and spatial and spectral morphologies, the non-parametric 1/V_max method was adopted. The price to pay to benefit from magnification is a reduction of the effective volume of the survey, together with a more complex analysis procedure to properly determine the effective volume V_max for each galaxy. In this paper we present a complete procedure for the determination of the LF based on IFU detections in lensing clusters. This procedure, including some new methods for masking, effective volume integration and (individual) completeness determinations, has been fully automated when possible, and it can be easily generalized to the analysis of IFU observations in blank fields.

Results. As a result of this analysis, the Lyman-alpha LF has been obtained in four different redshift bins: 2.9 <  z <  6, 7, 2.9 <  z <  4.0, 4.0 <  z <  5.0, and 5.0 <  z <  6.7 with constraints down to log L_Lyα = 40.5. From our data only, no significant evolution of LF mean slope can be found. When performing a Schechter analysis also including data from the literature to complete the present sample towards the brightest luminosities, a steep faint end slope was measured varying from α = −1.69_−0.08^+0.08 to α = −1.87_−0.12^+0.12 between the lowest and the highest redshift bins.

Conclusions. The contribution of the LAE population to the star formation rate density at z ∼ 6 is ≲50% depending on the luminosity limit considered, which is of the same order as the Lyman-break galaxy (LBG) contribution. The evolution of the LAE contribution with redshift depends on the assumed escape fraction of Lyman-alpha photons, and appears to slightly increase with increasing redshift when this fraction is conservatively set to one. Depending on the intersection between the LAE/LBG populations, the contribution of the observed galaxies to the ionizing flux may suffice to keep the universe ionized at z ∼ 6.