Bimodality of [α/Fe]-[Fe/H] distributions is a natural outcome of dissipative collapse and disc growth in Milky Way-type galaxies

Abstract

We present a set of self-consistent chemo-dynamical simulations of MW-type galaxies formation to study the origin of the bimodality of $\alpha$-elements in stellar populations. We explore how the bimodality is related to the geometrically and kinematically defined stellar discs, gas accretion and radial migration. We find that the two $\alpha$-sequences are formed in quite different physical environments. The high-$\alpha$ sequence is formed early from a burst of star formation (SF) in a turbulent, compact gaseous disc which forms a thick disc. The low-$\alpha$ stellar populations is the result of quiescent SF supported by the slow accretion of enriched gas onto a radially extended thin disc. Stellar feedback-driven outflows during the formation of the thick disc are responsible for the enrichment of the surrounding gaseous halo, which subsequently feeds the disc on a longer time-scale. During the thin disc phase, chemical evolution reaches an equilibrium metallicity and abundance, where the stars pile-up. This equilibrium metallicity decreases towards the outer disc, generating the ridgeline that forms the low-$\alpha$ sequence. We identify a second mechanism capable of creating a low-$\alpha$ sequence in one of our simulations. Rapid shutdown of the SF, provoked by the feedback at the end of the thick disc phase, suppresses the chemical enrichment of the halo gas, which, once accreted onto the star-forming disc, dilutes the ISM at the beginning of the thin disc formation. Both mechanisms can operate in a galaxy, but the former is expected to occur when SF efficiency ceases to be dominated by the formation of the thick disc, while the latter can occur in the inner regions. Being the result of the presence of low and high gas density environments, the bimodality is independent of any particular merger history, suggesting that it could be much more widespread than has been claimed.

22 pages, 19 figures, accepted for publication in MNRAS

References in corpus (37)

• Trigonometric Parallaxes of Massive Star Forming Regions: VI. Galactic Structure, Fundamental Parameters and Non-Circular Motions
• Combined CO & Dust Scaling Relations of Depletion Time and Molecular Gas Fractions with Cosmic Time, Specific Star Formation Rate and Stellar Mass
• Mass, Metal, and Energy Feedback in Cosmological Simulations
• Evidence for Two Early Accretion Events That Built the Milky Way Stellar Halo
• Rapid formation of exponential disks and bulges at high redshift from the dynamical evolution of clump cluster and chain galaxies
• Accretion of gas onto nearby spiral galaxies
• Constraining the Milky Way's Hot Gas Halo with OVII and OVII Emission Lines
• Tracing chemical evolution over the extent of the Milky Way's Disk with APOGEE Red Clump Stars
• Reconstructing the star formation history of the Milky Way disc(s) from chemical abundances
• ZFOURGE/CANDELS: On the Evolution of M* Galaxy Progenitors from z=3 to 0.5
• Disentangling the Galactic Halo with APOGEE: I. Chemical and Kinematical Investigation of Distinct Metal-Poor Populations
• Why stellar feedback promotes disc formation in simulated galaxies
• Origin of chemically distinct discs in the Auriga cosmological simulations
• A Magellanic Origin for the Warp of the Galaxy
• The AMBRE Project: chemical evolution models for the Milky Way thick and thin discs
• Bar quenching in gas-rich galaxies
• The imprint of clump formation at high redshift. I. A disc alpha-abundance dichotomy
• Predictions for the Angular Dependence of Gas Mass Flow Rate and Metallicity in the Circumgalactic Medium
• Stellar Kinematic Constraints on Galactic Structure Models Revisited: Bar and Spiral Arm Resonances
• The formation of stellar nuclear discs in bar-induced gas inflows
• The Rich Are Different: Evidence from the RAVE Survey for Stellar Radial Migration
• Quantifying stellar radial migration in an N-body simulation: blurring, churning, and the outer regions of galaxy discs
• An Iterative Method for Constructing Equilibrium Phase Models of Stellar Systems
• Resonances in Barred Galaxies
• Stellar migrations and metal flows -- Chemical evolution of the thin disc of a simulated Milky Way analogous galaxy
• Why the Milky Way's bulge is not only a bar formed from a cold thin disk
• Evidence of ongoing radial migration in NGC 6754: Azimuthal variations of the gas properties
• Revisiting long-standing puzzles of the Milky Way: the Sun and its vicinity as typical outer disk chemical evolution
• Hic sunt dracones: Cartography of the Milky Way spiral arms and bar resonances with Gaia Data Release 2
• Metallicity-dependendent kinematics and morphology of the Milky Way bulge
• From Diversity to Dichotomy, and Quenching: Milky-Way-Like and Massive-Galaxy Progenitors at 0.5<z<3.0
• Geometric properties of galactic discs with clumpy episodes
• The Milky Way as a High Redshift Galaxy: The Importance of Thick Disk Formation in Galaxies
• The Role of Cold Flows and Reservoirs in Galaxy Formation With Strong Feedback
• The Gaia-ESO Survey: Churning through the Milky Way
• The changing circumgalactic medium over the last 10 Gyr I: physical and dynamical properties
• The study of two barred galaxies with curious kinematical features

Cited by in corpus (45)

• VINTERGATAN I: The origins of chemically, kinematically and structurally distinct discs in a simulated Milky Way-mass galaxy
• APOGEE DR16: a multi-zone chemical evolution model for the Galactic disc based on MCMC methods
• VINTERGATAN II: the history of the Milky Way told by its mergers
• A Tale of Two Disks: Mapping the Milky Way with the Final Data Release of APOGEE
• Unveiling the time evolution of chemical abundances across the Milky Way disk with APOGEE
• Characterizing epochs of star formation across the Milky Way disc using age-metallicity distributions of GALAH stars
• On the origin of the Galactic thin and thick discs, their abundance gradients and the diagnostic potential of their abundance ratios
• The evolution of CNO elements in galaxies
• Beyond the two-infall model I. Indications for a recent gas infall with Gaia DR3 chemical abundances
• The Milky Way tomography with APOGEE: intrinsic density distribution and structure of mono-abundance populations
• Quantifying radial migration in the Milky Way: Inefficient over short timescales but essential to the very outer disc beyond ~15 kpc
• The challenge of simultaneously matching the observed diversity of chemical abundance patterns in cosmological hydrodynamical simulations
• Radial structure and formation of the Milky Way disc
• Neutron star mergers as the astrophysical site of the r-process in the Milky Way and its satellite galaxies
• From giant clumps to clouds -- II. The emergence of thick disc kinematics from the conditions of star formation in high redshift gas rich galaxies
• Chemical Evolution with Radial Mixing Redux: Extending beyond the Solar Neighborhood
• [Mg/Fe] ratios in the solar neighbourhood: stellar yields and chemical evolution scenarios
• Timing the Milky Way bar formation and the accompanying radial migration episode
• (Re)mind the gap: a hiatus in star formation history unveiled by APOGEE DR17
• The stellar halo in Local Group Hestia simulations III. Chemical abundance relations for accreted and in-situ stars
• The Pristine survey -- XV. A CFHT ESPaDOnS view on the Milky Way halo and disc populations
• Observational Constraints of Radial Migration in the Galactic Disc Driven by the Slowing Bar
• The AMBRE Project: Solar neighbourhood chemodynamical constraints on Galactic disc evolution
• Universal properties of the high- and low-α disk: small intrinsic abundance scatter and migrating stars
• The imprint of clump formation at high redshift. II. The chemistry of the bulge
• ISM metallicity variations across spiral arms in disk galaxies: the impact of local enrichment and gas migration in the presence of radial metallicity gradient
• Analytic solution of Chemical Evolution Models with Type Ia SNe
• Disc dichotomy signature in the vertical distribution of [Mg/Fe] and the delayed gas infall scenario
• The metal-poor end of the Spite plateau. II. Detailed chemical investigation
• Stellar migration in the Auriga simulations
• Evolution of the radial ISM metallicity gradient in the Milky Way disk since redshift $\approx 3$
• Metallicity-Suppressed Collapsars Cannot be the Dominant r-Process Source in the Milky Way
• Efficient radial migration by giant molecular clouds in the first several hundred Myr after the stellar birth
• Formation of Transitional cE/UCD Galaxies through Massive/Dwarf Disc Galaxy Mergers
• The GALAH Survey: Stellar parameters and abundances for 800,000 Gaia RVS spectra using GALAH DR4 and The Cannon
• Rediscovering the Milky Way with orbit superposition approach and APOGEE data I. Method validation
• Rediscovering the Milky Way with orbit superposition approach and APOGEE data II. Chrono-chemo-kinematics of the disc
• Bar-spiral interaction produces radial migration and star formation bursts
• Stellar Migration and Chemical Enrichment in the Milky Way Disc: A Hybrid Model
• The Milky Way in context: The formation of galactic discs and chemical sequences from a cosmological perspective
• Milky Way Mapper decoded abundances -- I. Shared disc enrichment patterns
• Neutron-capture elements record the ordered chemical evolution of the disc over time
• Rapid early gas accretion for the inner Galactic disc
• J-PLUS Reconstructing the Milky Way Disc's star formation history with twelve-filter photometry
• An ancient system hidden in the Galactic plane?