The Two-infall Model Revisited: Constraints on Milky Way Bulge Assembly from >30,000 Galactic Chemical Evolution Models and Machine Learning

Abstract

We constrain the formation history of the Milky Way bulge using a two-infall galactic chemical evolution (GCE) algorithm implemented in the N'OMEGA+ code. We recover a best-fit scenario in which the bulge forms through an early, rapid starburst ($t_1\sim 0.1$ Gyr, ${\tau }_1\sim 0.09$ Gyr, and star formation efficiency (SFE) $\sim 3{\mathrm{Gyr}}^{-1}$), followed by a delayed, lower-mass second infall ($t_2\sim 5.1$ Gyr, ${\tau }_2\sim 1.7$ Gyr, and ${\sigma }_2\sim 0.69$). Our model adopts mass- and metallicity-dependent nucleosynthetic yields from modern stellar grids and explores a wide GCE parameter space in infall timing, SFE, mass partitioning, initial mass function upper mass, and type Ia supernova normalization, optimized via a hybrid genetic algorithm with Markov Chain Monte Carlo refinement. The later infall features a reduced SFE ($\Delta \mathrm{SFE}\sim 0.72$), reproducing the metal-rich peak of the bulge metallicity distribution function (MDF) and the decline in [$\alpha$/Fe] at high [Fe/H]. Our model naturally favors the M. Joyce et al. age--metallicity relation over the ages in T. Bensby et al. Degeneracy and principal component analyses show that the infall history, SFE, and mass partitioning are strongly covariant---the bulge's observed MDF, abundance trends, and age distribution constrain only their combinations, not each parameter independently. The results support a composite bulge origin---an early, rapid collapse builds the majority of the mass, while a younger component is required to match the late-stage enrichment.

arXiv comment33 pages, 13 figures, 5 tables. Published in The Astrophysical Journal

References in corpus (115)

• Galactic Stellar and Substellar Initial Mass Function
• On the variation of the Initial Mass Function
• The Star Formation Law in Nearby Galaxies on Sub-Kpc Scales
• The Apache Point Observatory Galactic Evolution Experiment (APOGEE)
• Co-formation of the Galactic disc and the stellar halo
• Observational clues to the progenitors of Type-Ia supernovae
• Galactic Chemical Evolution: Hydrogen Through Zinc
• Chemical evolution with radial mixing
• Updated stellar yields from Asymptotic Giant Branch models
• Abundance Gradients and the Formation of the Milky Way
• Molecular Gas and Star Formation in Nearby Disk Galaxies
• Chemical Cartography with APOGEE: Metallicity Distribution Functions and the Chemical Structure of the Milky Way Disk
• Presupernova evolution and explosive nucleosynthesis of rotating massive stars in the metallicity range -3 <=[Fe/H]<= 0
• Simulations of Galaxy Formation in a Lambda CDM Universe II: The Fine Structure of Simulated Galactic Disks
• The ACS Survey of Galactic Globular Clusters. I. Overview and Clusters Without Previous HST Photometry
• Improved Estimates of the Milky Way's Stellar Mass and Star Formation Rate from Hierarchical Bayesian Meta-Analysis
• Simulations of Galaxy Formation in a Lambda CDM Universe I: Dynamical and Photometric Properties of a Simulated Disk Galaxy
• Evolution of the Hubble Sequence in Hierarchical Models for Galaxy Formation
• The Evolution of Isotope Ratios in the Milky Way Galaxy
• Mapping the Three-Dimensional Density of the Galactic Bulge with VVV Red Clump Stars
• Dynamical modelling of the Galactic bulge and bar: the Milky Way's bar pattern speed, stellar, and dark matter mass distribution
• The Structure of the Milky Way's Bar Outside the Bulge
• Our Milky Way as a Pure-Disk Galaxy -- A Challenge for Galaxy Formation
• The Metal Content of Bulge Field Stars from FLAMES-GIRAFFE Spectra. I. Stellar parameters and Iron Abundances
• Chemical evolution with rotating massive star yields: I. The solar neighbourhood and the s-process elements
• An upper limit to the masses of stars
• Evidence for Mature Bulges and an Inside-out Quenching Phase 3 Billion Years After the Big Bang
• The Hubble Higher-Z Supernova Search: Supernovae to z=1.6 and Constraints on Type Ia Progenitor Models
• Two Red Clumps and the X-Shaped Milky Way Bulge
• Inside Out and Upside Down: Tracing the Assembly of a Simulated Disk Galaxy Using Mono-Age Stellar Populations
• The rates of Type Ia Supernovae. I. Analytical Formulations
• Oxygen, Carbon and Nitrogen evolution in galaxies
• Spiral arms, bar shape and bulge microlensing in the Milky Way
• An excess of massive stars in the local 30 Doradus starburst
• Where stars form: inside-out growth and coherent star formation from HST Halpha maps of 2676 galaxies across the main sequence at z~1
• Sub-Chandrasekhar-mass white dwarf detonations revisited
• The Bulge Radial Velocity Assay (BRAVA): II. Complete Sample and Data Release
• The metallicity distribution of bulge clump giants in Baade's Window
• A time-resolved picture of our Milky Way's early formation history
• NuGrid stellar data set I. Stellar yields from H to Bi for stars with metallicities Z = 0.02 and Z = 0.01
• The Sausage Globular Clusters
• Chemodynamical history of the Galactic Bulge
• Chemical evolution of the Galactic bulge as traced by microlensed dwarf and subgiant stars. IV. Two bulge populations
• The s process in massive stars at low metallicity. Effect of primary N14 from fast rotating stars
• Alpha element abundances and gradients in the Milky Way bulge from FLAMES-GIRAFFE spectra of 650 K giants
• Chemical evolution of the Galactic bulge as traced by microlensed dwarf and subgiant stars. VI. Age and abundance structure of the stellar populations in the central sub-kpc of the Milky Way
• Galactic Archaeology with asteroseismic ages: evidence for delayed gas infall in the formation of the Milky Way disc
• On the Formation of Galactic Thick Disks
• Evolution of the Milky Way with radial motions of stars and gas I. The solar neighborhood and the thin and thick disk
• NuGrid Stellar Data Set. II. Stellar Yields from H to Bi for Stellar Models with Mzams = 1 to 25Msun and Z = 0.0001 to 0.02
• Insights on the Milky Way bulge formation from the correlations between kinematics and metallicity
• Confirming chemical clocks: asteroseismic age dissection of the Milky Way disk(s)
• Chemodynamics of barred galaxies in cosmological simulations: On the Milky Way's quiescent merger history and in-situ bulge
• Revisiting the Integrated Star Formation Law. II. Starbursts and the Combined Global Schmidt Law
• Stellar density profile and mass of the Milky Way Bulge from VVV data
• The mmax-Mecl relation, the IMF and IGIMF: probabilistically sampled functions?
• The Effect of Different Type Ia Supernova Progenitors on Galactic Chemical Evolution
• The Milky Way bar and bulge revealed by APOGEE DR16 and Gaia EDR3
• Reddening and metallicity maps of the Milky Way bulge from VVV and 2MASS III. The first global photometric metallicity map of the Galactic bulge
• Chemical Enrichment and Radial Migration in the Galactic Disk -- the origin of the [$\alpha /\mathrm{Fe}]$ Double Sequence
• The X-shaped Bulge of the Milky Way revealed by WISE
• Formation & evolution of the Galactic bulge: constraints from stellar abundances
• Detailed comparison of the structures and kinematics of simulated and observed barred galaxies
• Effects of radial flows on the chemical evolution of the Milky Way disk
• Selecting accreted populations: metallicity, elemental abundances, and ages of the Gaia-Sausage-Enceladus and Sequoia populations
• Before the Bar: Kinematic Detection of A Spheroidal Metal-Poor Bulge Component
• A boxy bulge in the Milky Way. Inversion of the stellar statistics equation with 2MASS data
• Constraining the structure and formation of the Galactic bulge from a field in its outskirts. FLAMES-GIRAFFE spectra of about 400 red giants around (l,b)=(0°,-10°)
• Empirical photometric calibration of the Gaia Red Clump: colours, effective temperature and absolute magnitude
• Galactic bulge formation as a maximum intensity starburst
• Age dating of an early Milky Way merger via asteroseismology of the naked-eye star $\nu$ Indi
• The Pristine Inner Galaxy Survey (PIGS) I: Tracing the kinematics of metal-poor stars in the Galactic bulge
• How Many Components? Quantifying the Complexity of the Metallicity Distribution in the Milky Way Bulge with APOGEE
• Galactic Archaeology with asteroseismic ages. II. Confirmation of a delayed gas infall using Bayesian analysis based on MCMC methods
• Metallicity Distribution Functions, Radial Velocities, and Alpha Element Abundances in Three Off-Axis Bulge Fields
• Single Degenerate Models for Type Ia Supernovae Progenitor's Evolution and Nucleosythesis Yields
• Efficient emulators of computer experiments using compactly supported correlation functions, with an application to cosmology
• Field Stars and Clusters of the Galactic Bulge: Implications for Galaxy Formation
• Chemodynamical Modelling of the Galactic Bulge and Bar
• NuGrid stellar data set - III. Updated low-mass AGB models and s-process nucleosynthesis with metallicities Z=0.01, Z=0.02 and Z=0.03
• Bar-formation as driver of gas inflows in isolated disc galaxies
• Chemical evolution of the Galactic bulge: different stellar populations and possible gradients
• The Close Binary Fraction as a Function of Stellar Parameters in APOGEE: A Strong Anti-Correlation With $\alpha$ Abundances
• Uncertainties in Galactic Chemical Evolution Models
• Effects of Galactic fountains and delayed mixing in the chemical evolution of the Milky Way
• Cosmology with galaxy-galaxy lensing on non-perturbative scales: Emulation method and application to BOSS LOWZ
• The Similarity of Abundance Ratio Trends and Nucleosynthetic Patterns in the Milky Way Disk and Bulge
• The origin of stellar populations in the Galactic bulge from chemical abundances
• Rates and delay times of type Ia supernovae in the Dark Energy Survey
• SDSS-IV MaNGA: The link between bars and the early cessation of star formation in spiral galaxies
• Validating Semi-Analytic Models of High-Redshift Galaxy Formation using Radiation Hydrodynamical Simulations
• New insights on the Galactic Bulge Initial Mass Function
• Metallicity-dependent nucleosynthetic yields of Type Ia supernovae originating from double detonations of sub-M${}_{\text{Ch}}$ white dwarfs
• Two-Component Galactic Bulge Probed with Renewed Galactic Chemical Evolution Model
• The Metallicity Distribution of the Milky Way Bulge
• Stellar populations across galaxy bars in the MUSE TIMER project
• Near-Infrared photometry of four metal-rich Bulge globular clusters: NGC6304, NGC6569, NGC6637, NGC6638
• The Ages of Galactic Bulge Stars with Realistic Uncertainties
• Stochastic Chemical Evolution of Radioactive Isotopes with a Monte Carlo Approach
• The Milky Way's bulge star formation history as constrained from its bimodal chemical abundance distribution
• The BaLROG project - II. Quantifying the influence of bars on the stellar populations of nearby galaxies
• The chemodynamics of prograde and retrograde Milky Way stars
• Weighing the two stellar components of the Galactic Bulge
• Mapping radial abundance gradients with Gaia-ESO open clusters: Evidence of recent gas accretion in the Milky Way disk
• Analytic solution of Chemical Evolution Models with Type Ia SNe
• Type Ia Supernova Nucleosynthesis: Metallicity-Dependent Yields
• Detailed $\alpha$ abundance trends in the inner Galactic bulge
• Evidence For Multiple Accretion Events in the $Gaia$-Sausage/Enceladus Structures
• Modeling Asteroseismic Yields for the Roman Galactic Bulge Time-Domain Survey
• Double X/Peanut Structures in Barred Galaxies -- Insights from an $N$--body Simulation
• Using chemical evolution models of the Milky Way disk to constrain Type Ia supernova progenitors
• Metallicity Properties of the Galactic Bulge Stars Near and Far: Expectations from the Auriga Simulation
• Chemical Abundances in the Milky Way's Nuclear Stellar Disc
• The oldest stars of the bulge: new information on the ancient Galaxy
• The impact of radial migration on disk galaxy star formation histories I. Biases in spatially resolved estimates