T. Hashimoto, T. Garel, B. Guiderdoni, A. Drake, R. Bacon, J. Blaizot, J. Richard, F. Leclercq, H. Inami, A. Verhamme, R. J. Bouwens, J. Brinchmann, C. M. Cantalupo, C. M. Carollo, J. Caruana, E. C. Herenz, J. Kerutt, R. A. Marino, P. Mitchell, J. Schaye

Abstract
We present rest-frame Lyα equivalent widths (EW₀) of 417 Lyα emitters (LAEs) detected with Multi Unit Spectroscopic Explorer (MUSE) on the Very Large Telescope (VLT) at 2.9 <z< 6.6 in the Hubble Ultra Deep Field. Based on the deep MUSE spectroscopy and ancillary Hubble Space Telescope (HST) photometry data, we carefully measured EW₀ values taking into account extended Lyα emission and UV continuum slopes (β). Our LAEs reach unprecedented depths, both in Lyα luminosities and UV absolute magnitudes, from log (L_Lyα/erg s^-1) ~ 41.0 to 43.0 and from M_UV ~ −16 to −21 (0.01−1.0 L^*_z=3). The EW₀ values span the range of ~ 5 to 240 Å or larger, and their distribution can be well fitted by an exponential law N = N0 exp(−EW₀/w₀). Owing to the high dynamic range in M_UV, we find that the scale factor, w₀, depends on M_UV in the sense that including fainter M_UV objects increases w₀, i.e., the Ando effect. The results indicate that selection functions affect the EW0 scale factor. Taking these effects into account, we find that our w₀ values are consistent with those in the literature within 1σ uncertainties at 2.9 < z < 6.6 at a given threshold of M_UV and L_Lyα. Interestingly, we find 12 objects with EW₀> 200 Å above 1σ uncertainties. Two of these 12 LAEs show signatures of merger or AGN activity: the weak C_IVλ1549 emission line. For the remaining 10 very large EW₀ LAEs, we find that the EW₀ values can be reproduced by young stellar ages (< 100 Myr) and low metallicities (≲ 0.02 Z_⊙). Otherwise, at least part of the Lyα emission in these LAEs needs to arise from anisotropic radiative transfer effects, fluorescence by hidden AGN or quasi-stellar object activity, or gravitational cooling.

Keywords
galaxies: high-redshift; galaxies: evolution; Galaxy: formation; early Universe; Astrophysics - Astrophysics of Galaxies

Astronomy & Astrophysics
Volume 608, Article Number A10, Number of pages 20
2017 December

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