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The MUSE Hubble Ultra Deep Field Survey. XV. The mean rest-UV spectra of Lyα emitters at z > 3

A. Feltre, M. V. Maseda, R. Bacon, J. Pradeep, F. Leclercq, H. Kusakabe, L. Wisotzki, T. Hashimoto, K. B. Schmidt, J. Blaizot, J. Brinchmann, L. A. Boogaard, S. Cantalupo, D. Carton, H. Inami, W. Kollatschny, R. A. Marino, J. Matthee, T. Nanayakkara, J. Richard, J. Schaye, L. Tresse, T. Urrutia, A. Verhamme, P. M. Weilbacher

We investigated the ultraviolet (UV) spectral properties of faint Lyman-α emitters (LAEs) in the redshift range 2.9 ≤ z ≤ 4.6, and we provide material to prepare future observations of the faint Universe. We used data from the MUSE Hubble Ultra Deep Survey to construct mean rest-frame spectra of continuum-faint (median MUV of −18 and down to MUV of −16), low stellar mass (median value of 108.4 M and down to 107 M) LAEs at redshift z ≳ 3. We computed various averaged spectra of LAEs, subsampled on the basis of their observational (e.g., Lyα strength, UV magnitude and spectral slope) and physical (e.g., stellar mass and star-formation rate) properties. We searched for UV spectral features other than Lyα, such as higher ionization nebular emission lines and absorption features. We successfully observed the O III]λ1666 and [C III]λ1907+C III]λ1909 collisionally excited emission lines and the He IIλ1640 recombination feature, as well as the resonant C IVλλ1548,1551 doublet either in emission or P-Cygni. We compared the observed spectral properties of the different mean spectra and find the emission lines to vary with the observational and physical properties of the LAEs. In particular, the mean spectra of LAEs with larger Lyα equivalent widths, fainter UV magnitudes, bluer UV spectral slopes, and lower stellar masses show the strongest nebular emission. The line ratios of these lines are similar to those measured in the spectra of local metal-poor galaxies, while their equivalent widths are weaker compared to the handful of extreme values detected in individual spectra of z >  2 galaxies. This suggests that weak UV features are likely ubiquitous in high z, low-mass, and faint LAEs. We publicly released the stacked spectra, as they can serve as empirical templates for the design of future observations, such as those with the James Webb Space Telescope and the Extremely Large Telescope.

galaxies: evolution; galaxies: high-redshift; ISM: lines and bands; ultraviolet: ISM; ultraviolet: galaxies; Astrophysics - Astrophysics of Galaxies; Astrophysics - Cosmology and Nongalactic Astrophysics

The average spectra computed in this work are only available at the CDS via anonymous ftp to ( or via

Based on observations made with ESO telescopes at the La Silla Paranal Observatory under programs 094.A-0289(B), 095.A-0010(A), 096.A-0045(A) and 096.A-0045(B).

Astronomy & Astrophysics
Volume 641, Article Number A118, Number of pages 26
2020 September

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Faculdade de Ciências da Universidade de Lisboa Universidade do Porto Faculdade de Ciências e Tecnologia da Universidade de Coimbra
Fundação para a Ciência e a Tecnologia COMPETE 2020 PORTUGAL 2020 União Europeia