Formation of N-rich field stars in the high-density building blocks of the Galactic bulge

Abstract

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_sun 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 (< 0.03). The mass fraction of NRS among all stars (f_nrs) can be higher than 1% within 0.5 Gyr timescale of star formation, if the mean stellar densities (rho_s) of the systems are higher than 0.1 M_sun/ 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.

18 pages, 12 figures, MNRAS in press

References in corpus (17)

• Cold Dark Clouds: The Initial Conditions for Star Formation
• Population Synthesis in the Blue IV: Accurate Model Predictions for Lick Indices and UBV Colors in Single Stellar Populations
• Evolution and nucleosynthesis of asymptotic giant branch stellar models of low metallicity
• The imprint of clump formation at high redshift. I. A disc alpha-abundance dichotomy
• Origin of Abundance Inhomogeneity in Globular Clusters
• APOGEE Chemical Abundances of the Sagittarius Dwarf Galaxy
• Dust-regulated galaxy formation and evolution:A new chemodynamical model with live dust particles
• Why the Milky Way's bulge is not only a bar formed from a cold thin disk
• Metallicity-dependendent kinematics and morphology of the Milky Way bulge
• Chemodynamics of newly identified giants with globular cluster like abundance patterns in the bulge, disk, and halo of the Milky Way
• The origin of stellar populations in the Galactic bulge from chemical abundances
• Purveyors of fine halos: Re-assessing globular cluster contributions to the Milky Way halo build-up with SDSS-IV
• The AIMSS Project II: Dynamical-to-Stellar Mass Ratios Across the Star Cluster - Galaxy Divide
• The origin of discrete multiple stellar populations in globular clusters
• Massive stars and globular cluster formation
• Gaia DR2 orbital properties for field stars with globular cluster-like CN band strengths
• An investigation of C, N and Na abundances in red giant stars of the Sculptor dwarf spheroidal galaxy

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• APOGEE discovery of a chemically atypical star disrupted from NGC 6723 and captured by the Milky Way bulge
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