First interferometric study of enhanced N-fractionation in
  N$_{2}$H$^{+}$: the high-mass star-forming region IRAS 05358+3543
  Nitrogen (N) fractionation is used as a tool to search for a link between the
chemical history of the Solar System and star-forming regions. A large
variation of $^{14}$N/$^{15}$N is observed towards different astrophysical
sources, and current chemical models cannot reproduce it. With the advent of
high angular resolution radiotelescopes it is now possible to search for
N-fractionation at core scales. We present IRAM NOEMA observations of the J=1-0
transition of N$_{2}$H$^{+}$, $^{15}$NNH$^{+}$ and N$^{15}$NNH$^{+}$ towards
the high-mass protocluster IRAS 05358+3543. We find $^{14}$N/$^{15}$N ratios
that span from $\sim$100 up to $\sim$220 and these values are lower or equal
than those observed with single-dish observations towards the same source.
Since N-fractionation changes across the studied region, this means that it is
regulated by local environmental effects. We find also the possibility, for one
of the four cores defined in the protocluster, to have a more abundant
$^{15}$NNH$^{+}$ with respect to N$^{15}$NNH$^{+}$. This is another indication
that current chemical models may be missing chemical reactions or may not take
into account other mechanisms, like photodissociation or grain surface
chemistry, that could be important.
