2017A&A...608A...7F

Non-resonant FeII* (λ2365, λ2396, λ2612, λ2626) emission can potentially trace galactic winds in emission and provide useful constraints to wind models. From the 3.15'x3.15' mosaic of the Hubble Ultra Deep Field (UDF) obtained with the VLT/MUSE integral field spectrograph, we identify a statistical sample of 40 FeII* emitters and 50 MgII (λλ2796,2803) emitters from a sample of 271 [OII]λλ3726,3729 emitters with reliable redshifts from z=0.85-1.50 down to 2x10^–18 (3σ)ergs/s/cm² (for [OII]), covering the M* range from 10⁸-10¹¹M_☉. The FeII* and MgII emitters follow the galaxy main sequence, but with a clear dichotomy. Galaxies with masses below 10⁹M_☉ and star formation rates (SFRs) of ≤1M_☉/yr have MgII emission without accompanying FeII* emission, whereas galaxies with masses above 10¹⁰M_☉ and SFRs≥10M_☉/yr have FeII* emission without accompanying MgII emission. Between these two regimes, galaxies have both MgII and FeII* emission, typically with MgII P Cygni profiles. Indeed, the MgII profile shows a progression along the main sequence from pure emission to P Cygni profiles to strong absorption, due to resonant trapping. Combining the deep MUSE data with HST ancillary information, we find that galaxies with pure MgII emission profiles have lower SFR surface densities than those with either MgII P Cygni profiles or FeII* emission. These spectral signatures produced through continuum scattering and fluorescence, MgII P Cygni profiles and FeII* emission, are better candidates for tracing galactic outflows than pure MgII emission, which may originate from HII regions. We compare the absorption and emission rest-frame equivalent widths for pairs of FeII transitions to predictions from outflow models and find that the observations consistently have less total re-emission than absorption, suggesting either dust extinction or non-isotropic outflow geometries.