Nitrogen abundance in the X-ray halos of clusters and groups of galaxies
  Chemical abundances in the X-ray halos (also known as the intracluster
medium, ICM) of clusters and groups of galaxies can be measured via prominent
emission line features in their X-ray spectra. Elemental abundances are
footprints of time-integrated yields of various stellar populations that have
left their specific abundance patterns prior to and during the cluster and
group evolution. We aim to constrain nitrogen abundances in the CHEmical
Evolution RGS Sample (CHEERS), which contains 44 nearby groups and clusters of
galaxies, in order to have a better understanding of their chemical enrichment.
We examine the high-resolution spectra of the CHEERS sample carefully and take
into account various systematic effects in the spectral modelling. We compare
the observed abundance ratios with those in the Galactic stellar populations,
as well as predictions from stellar yields (low- and intermediate-mass stars,
massive stars and degenerate stars). The nitrogen abundance can only be well
constrained ($\gtrsim3\sigma$) in one cluster of galaxies and seven groups of
galaxies. The [O/Fe] -- [Fe/H] relation of the ICM is comparable to that for
the Galaxy, while both [N/Fe] and [N/O] ratios of the ICM are higher than in
the Galaxy. Future studies on nitrogen radial distributions are required to
tell whether the obtained higher [N/Fe] and [N/O] ratios are biased due to the
small extraction region ($r/r_{500}\lesssim0.05$) that we adopt here. Since
abundances of odd-$Z$ elements are more sensitive to the initial metallicity of
stellar populations, accurate abundance measurements of N, Na and Al are
required to better constrain the chemical enrichment in the X-ray halos of
clusters and groups of galaxies.
