Understanding inverse metallicity gradients in galactic discs as a consequence of inside-out formation

Abstract

The early stages of a galaxy's evolution leave an imprint on its metallicity distribution. We discuss the origins and evolution of radial metallicity gradients in discs of spiral galaxies using an analytical chemical evolution model. We explain how radial metallicity gradients in stellar populations are determined by three factors: the radial metallicity profile of the star-forming ISM, radial changes in the star-formation history (in particular inside-out formation), and radial mixing of stars. Under reasonable assumptions, inside-out formation steepens the negative ISM metallicity gradient, but contributes positively to the stellar metallicity gradient, up to inverting the metallicity profile to a positive d[Fe/H]/dR. This reconciles steep negative d[Fe/H]/dR in some high redshift galaxies to generally flatter gradients in local observations. We discuss the evidence for inverse radial metallicity gradients (positive d[X/H]/dR) at high redshifts and the inverse relationship between azimuthal velocity and the metallicity (positive dV_ϕ/d[Fe/H]) of stars for the Milky Way's thick disc. The former can be achieved by high central gas-loss rates and re-distribution processes, e.g. re-accretion of enriched material in conjunction with inside-out formation, and near-disc galactic fountaining. For the Milky Way thick disc, we show that the positive dV_ϕ/d[Fe/H] correlation points to comparable timescales for inside-out formation, initial metal enrichment and SNIa enrichment. We argue that the original ISM metallicity gradient could be inferred with better data from the high-metallicity tail of the alpha enhanced population. Including inside-out formation in our models changes the local vertical metallicity gradient by about -0.2dex/kpc, in line with local measurements.

22 pages, 16 figures, published as MNRAS 467, 1154

References in corpus (2)

• Inflow, Outflow, Yields, and Stellar Population Mixing in Chemical Evolution Models
• Impacts of a Flaring Star-forming Disc and Stellar Radial Mixing on the Vertical Metallicity Gradient

Cited by in corpus (74)

• De Re Metallica: The cosmic chemical evolution of galaxies
• The Biggest Splash
• The GALAH survey and Gaia DR2: dissecting the stellar disc's phase space by age, action, chemistry and location
• Probing cosmic isotropy with a new X-ray galaxy cluster sample through the $L_{\text{X}}-T$ scaling relation
• On the origin of the chemical bimodality of disk stars: A tale of merger and migration
• Confirming chemical clocks: asteroseismic age dissection of the Milky Way disk(s)
• Measuring Radial Orbit Migration in the Milky Way Disk
• Distances and parallax bias in Gaia DR2
• Origin of chemically distinct discs in the Auriga cosmological simulations
• Sausage & Mash: The dual origin of the Galactic thick disc and halo from the gas-rich Gaia-Enceladus-Sausage merger
• The Inside-out Growth of the Galactic Disk
• Keeping it Cool: Much Orbit Migration, yet Little Heating, in the Galactic Disk
• APOGEE DR16: a multi-zone chemical evolution model for the Galactic disc based on MCMC methods
• Tree-ring structure of Galactic bar resonance
• On the metallicity dependance of the [Y/Mg] - age relation for solar type stars
• The physics of gas phase metallicity gradients in galaxies
• Stellar migrations and metal flows -- Chemical evolution of the thin disc of a simulated Milky Way analogous galaxy
• First gas-phase metallicity gradients of $0.1\lesssim z\lesssim 0.8$ galaxies with MUSE
• Chemical evolution of the Milky Way: constraints on the formation of the thick and thin discs
• Aurigaia: mock Gaia DR2 stellar catalogues from the Auriga cosmological simulations
• Unveiling the Distinct Formation Pathways of the Inner and Outer Discs of the Milky Way with Bayesian Machine Learning
• SDSS-IV MaNGA: Modelling the metallicity gradients of gas and stars - radially dependent metal outflow vs IMF
• Evolution of N/O ratios in galaxies from cosmological hydrodynamical simulations
• Chasing the impact of the Gaia-Sausage-Enceladus merger on the formation of the Milky Way thick disc
• Prospects for Measuring Abundances of >20 Elements with Low-resolution Stellar Spectra
• Impacts of a Flaring Star-forming Disc and Stellar Radial Mixing on the Vertical Metallicity Gradient
• On the origin of the mass-metallicity gradient relation in the local Universe
• Chemical and Kinematic Properties of the Galactic Disk from the LAMOST and Gaia Sample Stars
• Intermediate- and high-velocity clouds in the Milky Way I: covering factors and vertical heights
• Orbital tori for non-axisymmetric galaxies
• The chemical evolution of r-process elements from neutron star mergers: the role of a 2-phase interstellar medium
• Measuring bar pattern speeds from single simulation snapshots
• Intermediate- and high-velocity clouds in the Milky Way II: evidence for a Galactic fountain with collimated outflows and diffuse inflows
• Constraints on Radial Migration in Spiral Galaxies - II. Angular momentum distribution and preferential migration
• Yule-Simpson's paradox in Galactic Archaeology
• Inverse stellar population age gradients of post-starburst galaxies at z=0.8 with LEGA-C
• The innate origin of radial and vertical gradients in a simulated galaxy disc
• The Flattening Metallicity Gradient in the Milky Way's Thin Disk
• The Gas-phase Metallicity Profiles of Star-forming Galaxies in the Modified Accretion Disk Framework
• The structural evolution of galaxies with both thin and thick discs
• The chemodynamics of prograde and retrograde Milky Way stars
• Dynamics and Morphology of the Milky Way Spiral Arms from the Metallicity Distribution and Radial Mixing
• A dynamical view on stellar metallicity gradient diversity across the Hubble sequence with CALIFA
• Migration and kinematics in growing disc galaxies with thin and thick discs
• Metallicity distributions of mono-age stellar populations of the Galactic disc from the LAMOST Galactic spectroscopic surveys
• The GALAH Survey: Temporal Chemical Enrichment of the Galactic Disk
• Neutron Star Mergers as the Main Source of R-process: Natal Kicks And Inside-Out Evolution to The Rescue
• Galactic disc profiles and a universal angular momentum distribution from statistical physics
• The AMBRE Project: Solar neighbourhood chemodynamical constraints on Galactic disc evolution
• A Blueprint for the Milky Way's Stellar Populations. III. Spatial Distributions and Population Fractions of Local Halo Stars
• Radial migration and vertical action in N-body simulations
• When Cold Radial Migration is Hot: Constraints from Resonant Overlap
• Correlations between age, kinematics, and chemistry as seen by the RAVE survey
• Cardinal kinematics: I. Rotation fields of the APOGEE Survey
• The resolved chemical abundance properties within the interstellar medium of star-forming galaxies at $\text{z}\approx 1.5$
• The role of the halo magnetic field on accretion through High-Velocity Clouds
• The vertical metallicity gradients of mono-age stellar populations in the Milky Way with the RAVE and Gaia data
• The Milky Way Revealed by Variable Stars I: Sample Selection of RR Lyrae stars, and Evidence for the Merger History
• The Non-Axisymmetric Influence: Radius and Angle-Dependent Trends in a Barred Galaxy
• Insights into the Formation and Evolution History of the Galactic Disk System
• Metallicity-Suppressed Collapsars Cannot be the Dominant r-Process Source in the Milky Way
• Galactic r-process abundance feature shaped by radial migration
• The small boxy/peanut structure of the Milky Way traced by old stars
• Evidence of a large scale positive rotation-metallicity correlation in the Galactic thick disk
• The vertical structure of the spiral galaxy NGC 3501: first stages of the formation of a thin metal-rich disc
• The parametrization of gas flows in discs in the Auriga simulations
• On the radial metallicity gradient and radial migration effect of the Galactic disk
• The physical origin of positive metallicity radial gradients in high-redshift galaxies: insights from the FIRE-2 cosmological hydrodynamic simulations
• Constraints on $R$-process Nucleosynthesis from ${}^{129}$I and ${}^{247}$Cm in the Early Solar System
• The effects of Galactic model uncertainties on LISA observations of double neutron stars
• Chemical Evolution in Nuclear Stellar Discs
• Galactic Surveys in the Gaia Era
• Metallicity Structure in Galactic Longitude-Velocity Diagrams of the Milky Way Disk and FIRE-2 Simulations
• Blanco DECam Bulge Survey (BDBS) IV: Metallicity Distributions and Bulge Structure from 2.6 Million Red Clump Stars