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.

arXiv comment18 pages, 12 figures, MNRAS in press

References in corpus (56)

• The Structure of Cold Dark Matter Halos
• Cold Dark Clouds: The Initial Conditions for Star Formation
• Na-O Anticorrelation and HB. VII. The chemical composition of first and second-generation stars in 15 globular clusters from GIRAFFE spectra
• The Emergence of the Thick Disk in a CDM Universe
• Our Milky Way as a Pure-Disk Galaxy -- A Challenge for Galaxy Formation
• Population Synthesis in the Blue IV: Accurate Model Predictions for Lick Indices and UBV Colors in Single Stellar Populations
• Yields of AGB and SAGB models with chemistry of low- and high-metallicity Globular Clusters
• Oxygen, Carbon and Nitrogen evolution in galaxies
• Abundance patterns of multiple populations in Globular Clusters: a chemical evolution model based on yields from AGB ejecta
• Chemodynamical history of the Galactic Bulge
• ARGOS IV: The Kinematics of the Milky Way Bulge
• Chemical tagging with APOGEE: Discovery of a large population of N-rich stars in the inner Galaxy
• Short-lived star-forming giant clumps in cosmological simulations of z~2 disks
• Evolution and nucleosynthesis of asymptotic giant branch stellar models of low metallicity
• The Population of Giant Clumps in Simulated High-z Galaxies: In-situ and Ex-situ, Migration and Survival
• Secondary star formation within massive star clusters: Origin of multiple stellar populations in globular clusters
• The supernova rate and delay time distribution in the Magellanic Clouds
• Evidence for the Hierarchical Formation of the Galactic Spheroid
• The mmax-Mecl relation, the IMF and IGIMF: probabilistically sampled functions?
• Light-element Abundance Variations in the Milky Way Halo
• The imprint of clump formation at high redshift. I. A disc alpha-abundance dichotomy
• Coevolution of dust, gas, and stars in galaxies - I. Spatial distributions and scaling-relations of dust and molecular hydrogen
• Formation of the Young Massive Cluster R136 triggered by Tidally-driven Colliding HI Flows
• A lower fragmentation mass scale in high redshift galaxies and its implications on giant clumps: a systematic numerical study
• The Densest Galaxy
• Origin of Abundance Inhomogeneity in Globular Clusters
• APOGEE Chemical Abundances of the Sagittarius Dwarf Galaxy
• Bulge Formation via Mergers in Cosmological Simulations
• Dust-regulated galaxy formation and evolution:A new chemodynamical model with live dust particles
• Bulge growth through disk instabilities in high-redshift galaxies
• Why the Milky Way's bulge is not only a bar formed from a cold thin disk
• Metallicity gradients through disk Instability: A simple model for the Milky Way's boxy bulge
• Natures of a clump-origin bulge: a pseudobulge-like but old metal-rich bulge
• Massive Clumps in Local Galaxies: Comparisons with High-Redshift Clumps
• Chemical evolution of the Galactic bulge: different stellar populations and possible gradients
• The observational signature of the first H II regions
• 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
• Formation, vertex deviation and age of the Milky Way's bulge: input from a cosmological simulation with a late-forming bar
• 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
• Formation of the Galactic bulge from a two-component stellar disk: Explaining cylindrical rotation and vertical metallicity gradient
• Dynamical Orbital classification of selected N-rich stars with \textit{Gaia} DR2 astrometry
• Reconciling the Galactic Bulge Turnoff Age Discrepancy with Enhanced Helium Enrichment
• A new model for the multiple stellar populations within Terzan 5
• Chemical evolution of the Large Magellanic Cloud
• The origin of discrete multiple stellar populations in globular clusters
• Massive stars and globular cluster formation
• Formation of globular clusters with multiple stellar populations from massive gas clumps in high-z gas-rich dwarf galaxies
• Dissolved Massive Metal-Rich Globular Clusters Can Cause the Range of UV Upturn Strengths Found among Early-type Galaxies
• The rise and fall of the UV upturn: $z=0.3,0.55$ and $0.7$
• Clumpy galaxies in cosmological simulations: The effect of ISM model
• 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
• A possible physical connection between helium-rich stellar populations of massive globular clusters and the UV upturn of galactic spheroids

Cited by in corpus (18)

• The contribution of N-rich stars to the Galactic stellar halo using APOGEE red giants
• Aluminum Enhanced Metal-Poor Stars buried in the Inner Galaxy
• Blanco DECam Bulge Survey (BDBS) II: Project Performance, Data Analysis, and Early Science Results
• Dynamical Orbital classification of selected N-rich stars with \textit{Gaia} DR2 astrometry
• Purveyors of fine halos. II. Chemodynamical association of halo stars with Milky Way globular clusters
• The complex stellar system M 22: confirming abundance variations with high precision differential measurements
• Galactic ArchaeoLogIcaL ExcavatiOns (GALILEO) I. An updated census of APOGEE N-rich giants across the Milky Way
• APOGEE discovery of a chemically atypical star disrupted from NGC 6723 and captured by the Milky Way bulge
• APOGEE spectroscopic evidence for chemical anomalies in dwarf galaxies: The case of M~54 and Sagittarius
• Discovery of a large population of Nitrogen-Enhanced stars in the Magellanic Clouds
• Jurassic: A Chemically Anomalous Structure in the Galactic Halo
• On the Chemical and Kinematic Consistency Between N-rich Metal-poor Field Stars and Enriched Populations in Globular Clusters
• A model for GN-z11: top-heavy stellar initial mass functions in forming galactic nuclei and ultra-compact dwarfs
• An enquiry on the origins of N-rich stars in the inner Galaxy basedon APOGEE chemical compositions
• The search for extratidal star candidates around Galactic globular clusters NGC 2808, NGC 6266, and NGC 6397 with {\textit{Gaia}} DR2 astrometry
• Detailed analysis of a sample of field metal-poor N-rich dwarfs
• The COMBS Survey -- III. The Chemodynamical Origins of Metal-Poor Bulge Stars
• Purveyors of fine halos III. Chemical abundance analysis of a potential omega Cen associate