Nitrogen Abundances in Damped Ly-alpha Absorbers
  Nitrogen is thought to have both primary and secondary origins depending on
whether the seed carbon and oxygen are produced by the star itself (primary) or
already present in the interstellar medium (secondary) from which star forms.
DLA and sub-DLA systems with typical metallicities of -3.0<Z/Z_sun<-0.5 are
excellent tools to study nitrogen production. We made a search for nitrogen in
the ESO-UVES advanced data products (EUADP) database. In the EUADP database, we
find 10 new measurements and 9 upper limits of nitrogen. We further compiled
DLA/sub-DLA data from the literature with estimates available of nitrogen and
alpha-elements. This yields a total of 98 systems, i.e. the largest nitrogen
abundance sample investigated so far. In agreement with previous studies, we
indeed find a bimodal [N/alpha] behaviour: three-quarter systems show a mean
value of [N/alpha]=-0.87 with a scatter of 0.21 dex and one-quarter shows
ratios clustered at [N/alpha]=-1.43 with a lower dispersion of 0.13 dex. The
high [N/alpha] group is consistent with the blue compact dwarves and dwarf
irregular galaxies, suggesting primary nitrogen production. The low [N/alpha]
group is the lowest ever observed in any astrophysical site and probably
provides an evidence of the primary production by fast rotating massive stars
in young sites. Moreover, we find a transition between the two [N/alpha] groups
around [N/H]=-2.5. The transition is not abrupt and there are a few systems
lying in the transition region. Additional observations of DLAs/sub-DLAs below
[N/H]<-2.5 would provide more clues.
