The Vertical Metallicity Gradient of the Milky Way Disk: Transitions in [a/Fe] Populations

Abstract

Using G dwarfs from the Sloan Extension for Galactic Understanding and Exploration (SEGUE) survey, we have determined a vertical metallicity gradient over a large volume of the Milky Way's disk, and examined how this gradient varies for different [a/Fe] subsamples. This sample contains over 40,000 stars with low-resolution spectroscopy over 144 lines of sight. We employ the SEGUE Stellar Parameter Pipeline (SSPP) to obtain estimates of effective temperature, surface gravity, [Fe/H], and [a/Fe] for each star and extract multiple volume-complete subsamples of approximately 1000 stars each. Based on the survey's consistent target-selection algorithm, we adjust each subsample to determine an unbiased picture of the disk in [Fe/H] and [a/Fe]; consequently, each individual star represents the properties of many. The SEGUE sample allows us to constrain the vertical metallicity gradient for a large number of stars over a significant volume of the disk, between ~0.3 and 1.6 kpc from the Galactic plane, and examine the in situ structure, in contrast to previous analyses which are more limited in scope. This work does not pre-suppose a disk structure, whether composed of a single complex population or a distinct thin and thick disk component. The metallicity gradient is -0.243 +0.039 -0.053 dex/kpc for the sample as a whole, which we compare to various literature results. Each [a/Fe] subsample dominates at a different range of heights above the plane of the Galaxy, which is exhibited in the gradient found in the sample as a whole. Stars over a limited range in [a/Fe] show little change in median [Fe/H] with height. If we associate [a/Fe] with age, our consistent vertical metallicity gradients with [a/Fe] suggest that stars formed in different epochs exhibit comparable vertical structure, implying similar star-formation processes and evolution.

arXiv comment62 pages, 12 figures, accepted by The Astrophysical Journal

References in corpus (74)

• Maps of Dust IR Emission for Use in Estimation of Reddening and CMBR Foregrounds
• The Sloan Digital Sky Survey: Technical Summary
• The Seventh Data Release of the Sloan Digital Sky Survey
• The 2.5 m Telescope of the Sloan Digital Sky Survey
• SDSS-III: Massive Spectroscopic Surveys of the Distant Universe, the Milky Way Galaxy, and Extra-Solar Planetary Systems
• The Dartmouth Stellar Evolution Database
• The Sloan Digital Sky Survey Photometric Camera
• The u'g'r'i'z' Standard Star Network
• The Geneva-Copenhagen survey of the Solar neighbourhood: Ages, metallicities, and kinematic properties of 14,000 F and G dwarfs
• The Ninth Data Release of the Sloan Digital Sky Survey: First Spectroscopic Data from the SDSS-III Baryon Oscillation Spectroscopic Survey
• The Milky Way Tomography with SDSS: I. Stellar Number Density Distribution
• SEGUE: A Spectroscopic Survey of 240,000 stars with g=14-20
• The New Galaxy: Signatures of its Formation
• The Multi-Object, Fiber-Fed Spectrographs for SDSS and the Baryon Oscillation Spectroscopic Survey
• Radial Mixing in Galactic Discs
• The Tenth Data Release of the Sloan Digital Sky Survey: First Spectroscopic Data from the SDSS-III Apache Point Observatory Galactic Evolution Experiment
• Astrometric Calibration of the Sloan Digital Sky Survey
• Elemental Abundance Survey of The Galactic Thick Disk
• New constraints on the chemical evolution of the solar neighbourhood and Galactic disc(s). Improved astrophysical parameters for the Geneva-Copenhagen Survey
• The Third Data Release of the Sloan Digital Sky Survey
• A photometricity and extinction monitor at the Apache Point Observatory
• Chemical evolution with radial mixing
• Kinematics of Metal-Poor Stars in the Galaxy. III. Formation of the Stellar Halo and Thick Disk as Revealed from a Large Sample of Non-Kinematically Selected Stars
• alpha-, r-, and s-process element trends in the Galactic thin and thick disks
• Simulations of Galaxy Formation in a Lambda CDM Universe II: The Fine Structure of Simulated Galactic Disks
• The Milky Way Tomography with SDSS: II. Stellar Metallicity
• The Geneva-Copenhagen Survey of the Solar neighbourhood III. Improved distances, ages, and kinematics
• The age structure of stellar populations in the solar vicinity. Clues of a two-phase formation history of the Milky Way disk
• Riding the Spiral Waves: Implications of Stellar Migration for the Properties of Galactic Disks
• Chemodynamical evolution of the Milky Way disk I: The solar vicinity
• The spatial structure of mono-abundance sub-populations of the Milky Way disk
• A Spectroscopic Study of the Ancient Milky Way: F- and G-Type Stars in the Third Data Release of the Sloan Digital Sky Survey
• The Galactic Thick Disk Stellar Abundances
• The Emergence of the Thick Disk in a CDM Universe
• A New Mechanism for Radial Migration in Galactic Disks: Spiral-Bar Resonance Overlap
• The Geneva-Copenhagen Survey of the Solar neighbourhood II. New uvby calibrations and rediscussion of stellar ages, the G dwarf problem, age-metallicity diagram, and heating mechanisms of the disk
• The thick disks of spiral galaxies as relics from gas-rich, turbulent, clumpy disks at high redshift
• Origin and structure of the Galactic disc(s)
• The Milky Way has no thick disk
• Inside Out and Upside Down: Tracing the Assembly of a Simulated Disk Galaxy Using Mono-Age Stellar Populations
• The Genesis of the Milky Way's Thick Disk via Stellar Migration
• Oxygen Abundances in Nearby FGK Stars and the Galactic Chemical Evolution of the Local Disk and Halo
• Vertical distribution of Galactic disk stars I - Kinematics and metallicity
• Formation and Evolution of the Disk System of the Milky Way: [alpha/Fe] Ratios and Kinematics of the SEGUE G-Dwarf Sample
• Chemodynamics of the Milky Way. I. The first year of APOGEE data
• Radial migration in galactic disks caused by resonance overlap of multiple patterns: Self-consistent simulations
• On the galactic disc age-metallicity relation
• A Structural and Dynamical Study of Late-Type, Edge-On Galaxies: II. Vertical Color Gradients and the Detection of Ubiquitous Thick Disks
• Radial Migration Does Little for Galactic Disc Thickening
• Chemical Cartography with APOGEE: Large-scale Mean Metallicity Maps of the Milky Way
• Chemistry and Kinematics in the Solar Neighborhood: Implications for Stellar Populations and for Galaxy Evolution
• Galactic masers and the Milky Way circular velocity
• Observations of Thick Disks in the Hubble Space Telescope Ultra Deep Field
• The RAdial Velocity Experiment (RAVE): Third Data Release
• Nearby Supernova Rates from the Lick Observatory Supernova Search. IV. A Recovery Method for the Delay Time Distribution
• Kinematics and chemical properties of the Galactic stellar populations. The HARPS FGK dwarfs sample
• Radial mixing in the outer Milky Way disk caused by an orbiting satellite
• Metallicity Gradients in the Milky Way Disk as Observed by the SEGUE Survey
• Radial Mixing in Galactic Disks: The Effects of Disk Structure and Satellite Bombardment
• A Short Scale Length for the α-Enhanced Thick Disk of the Milky Way: Evidence from Low-Latitude SEGUE Data
• MaGICC Thick Disk I: Comparing a Simulated Disk Formed with Stellar Feedback to the Milky Way
• A spectroscopic survey of thick disc stars outside the solar neighbourhood
• The Emergence of the Thick Disk in a CDM Universe II: Colors and Abundance Patterns
• Galactic Globular and Open Clusters in the Sloan Digital Sky Survey. II. Test of Theoretical Stellar Isochrones
• Stellar diffusion in barred spiral galaxies
• Distance determination for RAVE stars using stellar models II: Most likely values assuming a standard stellar evolution scenario
• The Metallicity Distribution Functions of SEGUE G and K dwarfs: Constraints for Disk Chemical Evolution and Formation
• Chemical gradients in the Milky Way from the RAVE data. I. Dwarf stars
• The Kinematics of Thick Disks in Nine External Galaxies
• Lick Indices in the Thin and Thick Disks of Edge-On Disk Galaxies
• The Metallicity Gradient of the Thick Disk Based on Red Horizontal Branch Stars From SDSS DR8
• Metallicity Gradients of Thick Disk Dwarf Stars
• Binary Contamination in the SEGUE sample: Effects on SSPP Determinations of Stellar Atmospheric Parameters
• Tracing the vertical composition of disc galaxies through colour gradients

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• Chemical Cartography with APOGEE: Metallicity Distribution Functions and the Chemical Structure of the Milky Way Disk
• Tracing chemical evolution over the extent of the Milky Way's Disk with APOGEE Red Clump Stars
• Formation of In Situ Stellar Haloes in Milky Way-Mass Galaxies
• In the Galactic disk, stellar [Fe/H] and age predict orbits and precise [X/Fe]
• A Tale of Two Disks: Mapping the Milky Way with the Final Data Release of APOGEE
• Impacts of a Flaring Star-forming Disc and Stellar Radial Mixing on the Vertical Metallicity Gradient
• The GALAH survey: properties of the Galactic disk(s) in the solar neighbourhood
• Bridging the gap -- the disappearance of the intermediate period gap for fully convective stars, uncovered by new ZTF rotation periods
• Scaling K2. VI. Reduced Small Planet Occurrence in High Galactic Amplitude Stars
• Yule-Simpson's paradox in Galactic Archaeology
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• Effects of the selection function on metallicity trends in spectroscopic surveys of the Milky Way
• Local Stellar Kinematics from RAVE data - VII. Metallicity Gradients from Red Clump Stars
• The Gaia-ESO Survey: Oxygen abundance in the Galactic thin and thick disks
• The orbital evolution of UFDs and GCs in an evolving Galactic potential
• Disc dichotomy signature in the vertical distribution of [Mg/Fe] and the delayed gas infall scenario
• Extinction Law at a Distance up to 25 kpc toward the Galactic Poles
• Asymmetric Mean Metallicity Distribution of the Milky Way's Disk
• The vertical metallicity gradients of mono-age stellar populations in the Milky Way with the RAVE and Gaia data
• Metallicity Calibration and Photometric Parallax Estimation: II. SDSS photometry
• Metallicities of old open clusters: A new Galactic map
• Blanco DECam Bulge Survey (BDBS) IV: Metallicity Distributions and Bulge Structure from 2.6 Million Red Clump Stars