Physical conditions and element abundances in galaxies at redshift
  0.001<z<3.4 : evolution trends
  We have collected an heterogeneous sample of galaxies at redshifts
0.001<z<3.35 with the aim of exploring the evolution of the physical parameters
and of the element abundances calculated by modelling the observed spectra. The
evolution picture which results from our calculations shows that: 1) the
emitting gaseous clouds in both active galactic nuclei (AGN) and starburst (SB)
galaxies have a density broad peak at z=0.5 becoming less dense and more
elongated with time. 2) The Ha flux emitted from the AGN clouds has a maximum
at z= 0.1. 3) The observed star temperatures in SBs increase with time,
indicating younger stars in local galaxies. 4) The O/H relative abundances show
splitting between solar and 0.1 solar at 0.3<z<3. N/H also shows splitting in
this z range but it also has a broad flat maximum between z=0.1 and z=0.001. 5)
The AGN narrow line region and the regions surrounding the SB show
fragmentation at z >0.35. 6) Metallicity (in terms of O/H) correlates with Ha
luminosity (La) and therefore with the star formation rate with different
trends regarding SBs and AGNs for La > 10^{41} erg s^{-1}. A rough correlation
is seen also for N/H. There seems to be no correlation for low luminosity
galaxies.
