Chemical tagging with APOGEE: Discovery of a large population of N-rich
  stars in the inner Galaxy
  Formation of globular clusters (GCs), the Galactic bulge, or galaxy bulges in
general, are important unsolved problems in Galactic astronomy. Homogeneous
infrared observations of large samples of stars belonging to GCs and the
Galactic bulge field are one of the best ways to study these problems. We
report the discovery by APOGEE of a population of field stars in the inner
Galaxy with abundances of N, C, and Al that are typically found in GC stars.
The newly discovered stars have high [N/Fe], which is correlated with [Al/Fe]
and anti-correlated with [C/Fe]. They are homogeneously distributed across, and
kinematically indistinguishable from, other field stars in the same volume.
Their metallicity distribution is seemingly unimodal, peaking at [Fe/H]~-1,
thus being in disagreement with that of the Galactic GC system. Our results can
be understood in terms of different scenarios. N-rich stars could be former
members of dissolved GCs, in which case the mass in destroyed GCs exceeds that
of the surviving GC system by a factor of ~8. In that scenario, the total mass
contained in so-called "first-generation" stars cannot be larger than that in
"second-generation" stars by more than a factor of ~9 and was certainly
smaller. Conversely, our results may imply the absence of a mandatory genetic
link between "second generation" stars and GCs. Last, but not least, N-rich
stars could be the oldest stars in the Galaxy, the by-products of chemical
enrichment by the first stellar generations formed in the heart of the Galaxy.
