The origin of diverse $\alpha$-element abundances in galaxy discs

Abstract

Spectroscopic surveys of the Galaxy reveal that its disc stars exhibit a spread in $[\alpha /Fe]$ at fixed $[Fe/H]$, manifest at some locations as a bimodality. The origin of these diverse, and possibly distinct, stellar populations in the Galactic disc is not well understood. We examine the Fe and $\alpha$-element evolution of 133 Milky Way-like galaxies from the EAGLE simulation, to investigate the origin and diversity of their $[\alpha /Fe]$-$[Fe/H]$ distributions. We find that bimodal $[\alpha /Fe]$ distributions arise in galaxies whose gas accretion histories exhibit episodes of significant infall at both early and late times, with the former fostering more intense star formation than the latter. The shorter characteristic consumption timescale of gas accreted in the earlier episode suppresses its enrichment with iron synthesised by Type Ia SNe, resulting in the formation of a high-$[\alpha /Fe]$ sequence. We find that bimodality in $[\alpha /Fe]$ similar to that seen in the Galaxy is rare, appearing in approximately 5 percent of galaxies in our sample. We posit that this is a consequence of an early gas accretion episode requiring the mass accretion history of a galaxy's dark matter halo to exhibit a phase of atypically-rapid growth at early epochs. The scarcity of EAGLE galaxies exhibiting distinct sequences in the $[\alpha /Fe]$-$[Fe/H]$ plane may therefore indicate that the Milky Way's elemental abundance patterns, and its accretion history, are not representative of the broader population of $\sim L^{\star }$ disc galaxies.

19 Pages, 10 Figures, Submitted to MNRAS. Additional material related to the paper, including a movie, can be found at http://www.astro.ljmu.ac.uk/~astjmack/eagle-alpha.html

References in corpus (30)

• The NumPy array: a structure for efficient numerical computation
• The EAGLE project: Simulating the evolution and assembly of galaxies and their environments
• The EAGLE simulations of galaxy formation: calibration of subgrid physics and model variations
• The effect of photo-ionization on the cooling rates of enriched, astrophysical plasmas
• The Radial Velocity Experiment (RAVE): first data release
• The GALAH Survey: Scientific Motivation
• Chemical enrichment in cosmological, smoothed particle hydrodynamics simulations
• alpha-, r-, and s-process element trends in the Galactic thin and thick disks
• The Auriga Project: the properties and formation mechanisms of disc galaxies across cosmic time
• Inviscid SPH
• The GALAH Survey: Observational Overview and Gaia DR1 companion
• Tracing chemical evolution over the extent of the Milky Way's Disk with APOGEE Red Clump Stars
• On the Formation of Galactic Thick Disks
• The age-metallicity structure of the Milky Way disk
• Reconstructing the star formation history of the Milky Way disc(s) from chemical abundances
• The Structure and Dynamical Evolution of the Stellar Disk of a Simulated Milky Way-Mass Galaxy
• The Gaia-ESO Survey: metallicity and kinematic trends in the Milky Way bulge
• Origin of chemically distinct discs in the Auriga cosmological simulations
• Merger Rates of Dark-Matter Haloes
• Dissecting simulated disc galaxies II: the age-velocity relation
• The Extended HST Supernova Survey: The Rate of SNe Ia at z>1.4 Remains Low
• A radial age gradient in the geometrically thick disk of the Milky Way
• Chemical mixing in smoothed particle hydrodynamics simulations
• Why the Milky Way's bulge is not only a bar formed from a cold thin disk
• Dissecting simulated disc galaxies I: the structure of mono-age populations
• The relationship between mono-abundance and mono-age stellar populations in the Milky Way disk
• Size matters: abundance matching, galaxy sizes, and the Tully-Fisher relation in EAGLE
• Scalelength of disc galaxies
• The vertical structure of gaseous galaxy discs in cold dark matter halos
• Kinematics in the Galactic Bulge with APOGEE: II. High-Order Kinematical Moments and Comparison to Extragalactic Bar Diagnostics

Cited by in corpus (78)

• The formation and assembly history of the Milky Way revealed by its globular cluster population
• The origin of accreted stellar halo populations in the Milky Way using APOGEE, $\text{Gaia}$, and the EAGLE simulations
• Evidence from APOGEE for the presence of a major building block of the halo buried in the inner Galaxy
• Dynamical heating across the Milky Way disc using APOGEE and $Gaia$
• Galactic Archaeology with asteroseismic ages: evidence for delayed gas infall in the formation of the Milky Way disc
• Age dissection of the Milky Way discs: red giants in the Kepler field
• From the bulge to the outer disc: StarHorse stellar parameters, distances, and extinctions for stars in APOGEE DR16 and other spectroscopic surveys
• VINTERGATAN I: The origins of chemically, kinematically and structurally distinct discs in a simulated Milky Way-mass galaxy
• Chemical Cartography with APOGEE: Multi-element abundance ratios
• Chronologically dating the early assembly of the Milky Way
• Chemical Enrichment and Radial Migration in the Galactic Disk -- the origin of the [$\alpha /\mathrm{Fe}]$ Double Sequence
• The imprint of clump formation at high redshift. I. A disc alpha-abundance dichotomy
• Weighing the stellar constituents of the Galactic halo with APOGEE red giant stars
• VINTERGATAN II: the history of the Milky Way told by its mergers
• Stellar migrations and metal flows -- Chemical evolution of the thin disc of a simulated Milky Way analogous galaxy
• Feedback from supermassive black holes transforms centrals into passive galaxies by ejecting circumgalactic gas
• Formation histories of stars, clusters and globular clusters in the E-MOSAICS simulations
• APOGEE DR14/DR15 Abundances in the Inner Milky Way
• A Tale of Two Disks: Mapping the Milky Way with the Final Data Release of APOGEE
• Nitrogen enrichment and clustered star formation at the dawn of the Galaxy
• Bimodality of [α/Fe]-[Fe/H] distributions is a natural outcome of dissipative collapse and disc growth in Milky Way-type galaxies
• The oxygen abundance gradients in the gas discs of galaxies in the EAGLE simulation
• Galactic Simulations of r-process Elemental Abundances
• The age-chemical abundance structure of the Galactic disc II: $\alpha$-dichotomy and thick disc formation
• The Stellar Halo of the Galaxy is Tilted & Doubly Broken
• VINTERGATAN III: how to reset the metallicity of the Milky Way
• Unveiling the time evolution of chemical abundances across the Milky Way disk with APOGEE
• The SLUGGS Survey: Measuring globular cluster ages using both photometry and spectroscopy
• Constraints on the assembly history of the Milky Way's smooth, diffuse stellar halo from the metallicity-dependent, radially-dominated velocity anisotropy profiles probed with K giants and BHB stars using LAMOST, SDSS/SEGUE, and Gaia
• The contribution of N-rich stars to the Galactic stellar halo using APOGEE red giants
• The evolution of CNO elements in galaxies
• The K2 Galactic Archaeology Program Data Release 3: Age-abundance patterns in C1-C8 and C10-C18
• Chemical Cartography with APOGEE: Mapping Disk Populations with a Two-Process Model and Residual Abundances
• The Milky Way tomography with APOGEE: intrinsic density distribution and structure of mono-abundance populations
• Age-chemical abundance structure of the Galaxy I: Evidence for a late accretion event in the outer disc at z ~ 0.6
• Predicting accreted satellite galaxy masses and accretion redshifts based on globular cluster orbits in the E-MOSAICS simulations
• The challenge of simultaneously matching the observed diversity of chemical abundance patterns in cosmological hydrodynamical simulations
• Geometric properties of galactic discs with clumpy episodes
• A Comparative Analysis of the Chemical Compositions of Gaia-Enceladus/Sausage and Milky Way Satellites using APOGEE
• The [α/Fe]-[Fe/H] relation in the E-MOSAICS simulations: its connection to the birth place of globular clusters and the fraction of globular cluster field stars in the bulge
• APOGEE [C/N] Abundances Across the Galaxy: Migration and Infall from Red Giant Ages
• The kinematics of globular cluster populations in the E-MOSAICS simulations and their implications for the assembly history of the Milky Way
• [Mg/Fe] ratios in the solar neighbourhood: stellar yields and chemical evolution scenarios
• Are the Milky Way and Andromeda unusual? A comparison with Milky Way and Andromeda Analogs
• Elemental Abundances in M31: Gradients in the Giant Stellar Stream
• Timing the Milky Way bar formation and the accompanying radial migration episode
• An [$\alpha$/Fe]-enhanced thick disk in a Milky Way Analogue
• The stellar halo in Local Group Hestia simulations II. The accreted component
• Variations in $\alpha$-element ratios trace the chemical evolution of the disk
• The stellar halo in Local Group Hestia simulations III. Chemical abundance relations for accreted and in-situ stars
• Mapping radial abundance gradients with Gaia-ESO open clusters: Evidence of recent gas accretion in the Milky Way disk
• The assembly history of the Galactic inner halo inferred from alpha-patterns
• The imprint of clump formation at high redshift. II. The chemistry of the bulge
• High- and Low-$\alpha$ Disk Stars Separate Dynamically at all Ages
• The globular cluster system of the Auriga simulations
• An enquiry on the origins of N-rich stars in the inner Galaxy basedon APOGEE chemical compositions
• Galactic Chemical Evolution Models Favor an Extended Type Ia Supernova Delay-Time Distribution
• Explaining the chemical trajectories of accreted and in-situ halo stars of the Milky Way
• Stellar populations and origin of thick disks in AURIGA simulations
• Gas accretion in Milky Way-like galaxies: temporal and radial dependencies
• Chemodynamical Analysis of Metal-rich High-eccentricity Stars in the Milky Way's Disk
• Predicting the water content of interstellar objects from galactic star formation histories
• The chemical enrichment of the Milky Way disk evaluated using conditional abundances
• The GALAH Survey: Dependence of elemental abundances on age and metallicity for stars in the Galactic disc
• Rediscovering the Milky Way with orbit superposition approach and APOGEE data II. Chrono-chemo-kinematics of the disc
• On the variation in stellar $\alpha$-enhancements of star-forming galaxies in the EAGLE simulation
• A Galactic Self-Portrait: Density Structure and Integrated Properties of the Milky Way Disk
• Stellar Migration and Chemical Enrichment in the Milky Way Disc: A Hybrid Model
• The building blocks of the Milky Way halo using APOGEE and Gaia -- or -- Is the Galaxy a typical galaxy?
• The Milky Way in context: The formation of galactic discs and chemical sequences from a cosmological perspective
• Chemical tagging with APOGEE, MUSE, and HST: constraints on the formation of $\omega$ Centauri
• Inferring Galactic Parameters from Chemical Abundances: A Multi-Star Approach
• The SAMI Survey: Evidence for dynamical coupling of ionised gas and young stellar populations
• Modelling the chemical evolution of the Milky Way
• New families in our Solar neighborhood: applying Gaussian Mixture models for objective classification of structures in the Milky Way and in simulations
• The origin of metal-poor and metal-rich globular clusters in E-MOSAICS
• A Tilt in the Dark Matter Halo of the Galaxy
• Neutron-capture elements record the ordered chemical evolution of the disc over time