Lyman-α emitters in the context of hierarchical galaxy formation: predictions for VLT/MUSE surveys

The VLT/Multi Unit Spectrograph Explorer (MUSE) integral-field spectrograph can detect Ly alpha emitters (LAE) in the redshift range 2.8 less than or similar to z less than or similar to 6.7 in a homogeneous way. Ongoing MUSE surveys will notably probe faint Ly alpha sources that are usually missed by current narrow-band surveys. We provide quantitative predictions for a typical wedding-cake observing strategy with MUSE based on mock catalogues generated with a semi-analytic model of galaxy formation coupled to numerical Ly alpha radiation transfer models in gas outflows. We expect approximate to 1500 bright LAEs (F-Ly alpha greater than or similar to 10(-17) erg s(-1) cm(-2)) in a typical shallow field (SF) survey carried over approximate to 100 arcmin(2), and approximate to 2000 sources as faint as 10(-18) erg s(-1) cm(-2) in a medium-deep field (MDF) survey over 10 arcmin(2). In a typical deep field (DF) survey of 1 arcmin(2), we predict that approximate to 500 extremely faint LAEs (F-Ly alpha greater than or similar to 4 x 10(-19) erg s(-1) cm(-2)) will be found. Our results suggest that faint Ly alpha sources contribute significantly to the cosmic Ly alpha luminosity and SFR budget. While the host haloes of bright LAEs at z approximate to 3 and 6 have descendants with median masses of 2 x 10(12) and 5 x 10(13) M-circle dot, respectively, the faintest sources detectable by MUSE at these redshifts are predicted to reside in haloes which evolve into typical sub-L* and L* galaxy haloes at z = 0. We expect typical DF and MDF surveys to uncover the building blocks of Milky Way-like objects, even probing the bulk of the stellar mass content of LAEs located in their progenitor haloes at z approximate to 3.