Extreme-emission-line galaxies in the MUSE Hubble Ultra Deep Field Survey

Aims . We aim to apply a methodology to build a sample of extreme-emission-line galaxies (EELGs) using integral field spectroscopy data. In this work, we followed the spectroscopic criteria corresponding to EELG selection and used the MUSE Hubble Ultra-Deep Field Survey, which includes the deepest spectroscopic survey ever performed. Methods . Objects in the primary (extended) sample were detected requiring a rest-frame equivalent width of EWo ⩾300 Å (200 Å ≤ EWo ≤ 300 Å) in any of the emission lines of [O II ] λλ 3726, 7329, [O III ] λλ 5007, 4959, or H α . A detailed closer inspection of the spectra of the candidates selected has been performed on a one-by-one basis in order to confirm their classification. For this sample, the line fluxes, physical properties, and chemical abundances of the EELGs have been derived, as well as their spatially resolved structure and kinematics. Results . Four (five) of the galaxies in the primary (extended) sample, ~57% (~83%), were spatially resolved. Three (none) of them present a clear pattern compatible with rotation. We show how our entire EELG sample shares the same loci defined by high-redshift galaxies (ɀ ≈ 6–8) for the mass-metallicity relation, illustrating their role as local analogs.