  We investigate the properties of strong (Hb+[OIII]) emitters before and after
the end of the Epoch of Reionization from z=8 to z=5.5. We make use of
ultra-deep JWST/NIRCam imaging in the Parallel Field of the MIRI Deep Imaging
Survey (MIDIS) in the Hubble eXtreme Deep Field (P2-XDF), in order to select
prominent (Hb+[OIII]) emitters (with rest EW_0 > 100 Angstroms) at z=5.5-7,
based on their flux density enhancement in the F356W band with respect to the
spectral energy distribution continuum. We complement our selection with other
(Hb+[OIII]) emitters from the literature at similar and higher (z=7-8)
redshifts. We find (non-independent) anti-correlations between EW_0(Hb+[OIII])
and both galaxy stellar mass and age, in agreement with previous studies, and a
positive correlation with specific star formation rate (sSFR). On the SFR-M*
plane, the (Hb+[OIII]) emitters populate both the star-formation main sequence
and the starburst region, which become indistinguishable at low stellar masses
(log10(M*) < 7.5). We find tentative evidence for a non-monotonic relation
between EW_0(Hb+[OIII]) and SFR, such that both parameters correlate with each
other at SFR > 1 Msun/yr, while the correlation flattens out at lower SFRs.
This suggests that low metallicities producing high EW_0(Hb+[OIII]) could be
important at low SFR values. Interestingly, the properties of the strong
emitters and other galaxies (33% and 67% of our z=5.5-7 sample, respectively)
are similar, including, in many cases, high sSFR. Therefore, it is crucial to
consider both emitters and non-emitters to obtain a complete picture of the
cosmic star formation activity around the Epoch of Reionization.
