Recent observational studies of the Galactic bulge by APOGEE have revealed that about 1 % of the bulge stars have rather high nitrogen abundances ( [ N/Fe ] > 0.5 ) .
We here numerically investigate in what physical conditions these N-rich stars ( NRS ) can be formed in spherical and disky stellar systems with stellar masses of 10 ^ { 7 } -10 ^ { 9 } { M } _ { \odot } that are the bulge ’ s building blocks .
The principal results are as follows .
A large fraction ( > 0.5 ) of new stars formed from interstellar medium polluted ( ISM ) by ejecta of asymptotic giant branch stars can have [ N/Fe ] > 0.5 within stellar systems , if the gas mass fraction of ISM ( f _ { g } ) is low ( \leq 0.03 ) .
The mass fraction of NRS among all stars ( f _ { nrs } ) can be higher than \approx 1 % within \approx 0.5 Gyr timescale of star formation , if the mean stellar densities ( \rho _ { s } ) of the systems are higher than \approx 0.1 { M } _ { \odot } pc ^ { -3 } .
The [ N/Fe ] distributions depend on \rho _ { s } , f _ { g } , and age distributions of their host stellar systems .
NRS have compact and disky spatial distributions within their host systems and have rotational kinematics .
Based on these results , we propose that the vast majority of the bulge ’ s NRS originate not from globular clusters ( GCs ) but from its high-density building blocks .
We suggest that NRS in the Galactic stellar halo have the same origin as those in the bulge .
We also suggest that low-density dwarf spheroidal and gas-rich dwarfs are unlikely to form NRS .
GCs are not only the formation sites of NRS .