The MUSE Hubble Ultra Deep Field Survey X. Ly$α$ Equivalent Widths at $2.9 < z < 6.6$

Abstract

We present rest-frame Lyα equivalent widths (EW 0 ) 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 EW 0 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 EW 0 values span the range of ∼ 5 to 240 Å or larger, and their distribution can be well fitted by an exponential law N = N 0 exp(−EW 0 /w 0 ). Owing to the high dynamic range in M UV , we find that the scale factor, w 0 , depends on M UV in the sense that including fainter M UV objects increases w 0 , i.e., the Ando effect. The results indicate that selection functions affect the EW 0 scale factor. Taking these effects into account, we find that our w 0 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 EW 0 > 200 Å above 1σ uncertainties. Two of these 12 LAEs show signatures of merger or AGN activity: the weak Civ λ1549 emission line. For the remaining 10 very large EW 0 LAEs, we find that the EW 0 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.

BlueMUSE: Project Overview and Science Cases

“…17. As demonstrated by MUSE studies, BlueMUSE will be particularly efficient at detecting the faintest population of z ∼ 3 galaxies (Drake et al, 2017;Hashimoto et al, 2017). These low mass objects are plausibly strong leakers according to previous observations (Izotov et al, 2018a) and simulations (Wise et al, 2014;Trebitsch et al, 2017;Kimm et al, 2019), and may correspond to the analogues of the sources of reionisation.…”

“…The second feature, which really makes MUSE a transformative instrument, is its unprecedented and unique sensitivity to emission lines. This has led to an impressive revision of the census of distant star-forming galaxies, including the discovery of very high equivalent width LAEs without HST counterparts and extremely faint UV magnitudes (average AB ∼ 32)(Bacon et al, 2017;Maseda et al, 2018), the robust detection of numerous LAEs, the assessment of the evolution of their luminosity function(Drake et al, 2017) and the characterisation of their equivalent widths(Hashimoto et al, 2017). Perhaps uniquely, this ability to detect line emission has led MUSE to discover and characterize extended Lyman-α haloes around most small galaxies(Wisotzki et al, 2016;Leclercq et al, 2017), or O ii gaseous structures in galaxy groups(Epinat et al, 2018), and tentative evidence of ouflows seen in Fe ii fluorescent lines(Finley et al, 2017b).…”