Large Metallicity Variations in the Galactic Interstellar Medium

Abstract

The Interstellar Medium (ISM) comprises gases at different temperatures and densities, including ionized, atomic, molecular species, and dust particles. The neutral ISM is dominated by neutral hydrogen and has ionization fractions up to 8%. The concentration of chemical elements heavier than helium (metallicity) spans orders of magnitudes in Galactic stars, because they formed at different times. Instead, the gas in the Solar vicinity is assumed to be well mixed and have Solar metallicity in traditional chemical evolution models. The ISM chemical abundances can be accurately measured with UV absorption-line spectroscopy. However, the effects of dust depletion, which removes part of the metals from the observable gaseous phase and incorporates it into solid grains, have prevented, until recently, a deeper investigation of the ISM metallicity. Here we report the dust-corrected metallicity of the neutral ISM measured towards 25 stars in our Galaxy. We find large variations in metallicity over a factor of 10 (with an average 55 +/- 7% Solar and standard deviation 0.28 dex) and including many regions of low metallicity, down to ~17% Solar and possibly below. Pristine gas falling onto the disk in the form of high-velocity clouds can cause the observed chemical inhomogeneities on scales of tens of pc. Our results suggest that this low-metallicity accreting gas does not efficiently mix into the ISM, which may help us understand metallicity deviations in nearby coeval stars.

arXiv commentThis version of the article has been accepted for publication on Nature, after peer review, but is not the Version of Record (http://dx.doi.org/10.1038/s41586-021-03780-0) and does not reflect post-acceptance improvements, or any corrections. An Addendum is included at the end of the article and is published here: https://www.nature.com/articles/s41586-022-04811-0

References in corpus (38)

• Gaia Data Release 2. Summary of the contents and survey properties
• The Gaia mission
• The Chemical Evolution of the Galaxy: the two-infall model
• A Unified Representation of Gas-Phase Element Depletions in the Interstellar Medium
• Mass models of the Milky Way
• Gaseous Galaxy Halos
• A reappraisal of the chemical composition of the Orion nebula based on VLT echelle spectrophotometry
• Mixing Time Scales in a Supernova-Driven Interstellar Medium
• Ultraviolet Extinction Properties in the Milky Way
• Mapping metallicity variations across nearby galaxy disks
• A Reservoir of Ionized Gas in the Galactic Halo to Sustain Star Formation in the Milky Way
• Metallicity Gradients in the Milky Way Disk as Observed by the SEGUE Survey
• The Fate of High-Velocity Clouds: Warm or Cold Cosmic Rain?
• The Far Ultraviolet Spectroscopic Explorer Survey of OVI Absorption in the Disk of the Milky Way
• Evolution of the dust-to-metals ratio in high-redshift galaxies probed by GRB-DLAs
• The Galactic radial abundance gradients of C, N, O, Ne, S, Cl and Ar from deep spectra of H II regions
• The chemical composition of the Orion star forming region: I. Homogeneity of O and Si abundances in B-type stars
• A Procedure for Correcting the Apparent Optical Depths of Moderately Saturated Interstellar Absorption Lines
• The cosmic evolution of dust-corrected metallicity in the neutral gas
• The chemical composition of the Orion star-forming region: II. Stars, gas, and dust: the abundance discrepancy conundrum
• Revisiting the radial abundance gradients of nitrogen and oxygen of the Milky Way
• Measuring the mixing scale of the ISM within nearby spiral galaxies
• The Mass Inflow and Outflow Rates of the Milky Way
• Small-Scale Interstellar Na I Structure Toward M92
• The Fractional Ionization of the Warm Neutral Interstellar Medium
• Atomic Data Revisions for Transitions Relevant to Observations of Interstellar, Circumgalactic, and Intergalactic Matter
• METAL: The Metal Evolution, Transport, and Abundance in the Large Magellanic Cloud Hubble program. II. Variations of interstellar depletions and dust-to-gas ratio within the LMC
• Measurements of the f-Values of the Resonance Transitions of Ni II at 1317.217A and 1370.132A
• Gas-phase Metallicity as a Diagnostic of the Drivers of Star-formation on Different Spatial Scales
• Gas Accretion onto the Milky Way
• Revealing the physical properties of gas accreting to haloes in the EAGLE simulations
• MusE GAs FLOw and Wind (MEGAFLOW) V. The dust/metallicity-anisotropy of the Circum-Galactic Medium
• Metals and dust in the neutral ISM: the Galaxy, Magellanic Clouds, and damped Lyman-α absorbers
• Mixing between High Velocity Clouds and the Galactic Halo
• Atomic data for Zn II - Improving Spectral Diagnostics of Chemical Evolution in High-redshift Galaxies
• HD 62542: Probing the Bare, Dense Core of a Translucent Interstellar Cloud
• A Closer Look at Some Gas-Phase Depletions in the ISM: Trends for O, Ge, and Kr vs. $F_{\ast }$, $f({\mathrm{H}}_2)$, and Starlight Intensity
• Interstellar absorptions towards the LMC: Small-scale density variations in Milky Way disc gas

Cited by in corpus (45)

• Gradients of chemical abundances in the Milky Way from HII regions: distances derived from Gaia EDR3 parallaxes and temperature inhomogeneities
• MUSE Analysis of Gas around Galaxies (MAGG) -- IV: The gaseous environment of $z\sim$ 3-4 Lyman-alpha emitting galaxies
• LAMOST meets Gaia: The Galactic Open Clusters
• CHAOS VII: A Large-Scale Direct Abundance Study in M33
• THEMIS 2.0: A self-consistent model for dust extinction, emission, and polarisation
• The chemical signature of the Galactic spiral arms revealed by Gaia DR3
• Dust depletion of metals from local to distant galaxies I: Peculiar nucleosynthesis effects and grain growth in the ISM
• Dissecting the interstellar medium of a z=6.3 galaxy: X-shooter spectroscopy and HST imaging of the afterglow and environment of the Swift GRB 210905A
• About Metallicity Variations in the Local Galactic Interstellar Medium
• Reliability and limitations of inferring birth radii in the Milky Way disk
• Dust depletion of of metals from local to distant galaxies II: Cosmic dust-to-metal ratio and dust composition
• The cerium content of the Milky Way as revealed by Gaia DR3 GSP-Spec abundances
• The Distribution of Metallicities in the Local Galactic Interstellar Medium
• A New Precise Determination of the Primordial Abundance of Deuterium: Measurement in the metal-poor sub-DLA system at z=3.42 towards quasar J1332+0052
• A High Precision Survey of the D/H Ratio in the Nearby Interstellar Medium
• A geostatistical analysis of multiscale metallicity variations in galaxies [II]: Predicting the metallicities of Hii and diffuse ionised gas regions via universal kriging
• Interstellar Extinction and Elemental Abundances: Individual Sight Lines
• Comprehensive UV and Optical spectral analysis of Cygnus X-1: Stellar and wind parameters, abundances, and evolutionary implications
• Spatially resolved study of the SS 433/W50 west region with Chandra: X-ray structure and spectral variation of non-thermal emission
• Caught in the Act: A Metal-Rich High-Velocity Cloud in the Inner Galaxy
• Constraints on the history of Galactic spiral arms revealed by Gaia GSP-Spec alpha-elements
• Formation and fate of low metallicity stars in IllustrisTNG50
• Presolar grains
• Impact of Radiation Feedback on the Formation of Globular Cluster Candidates during Cloud-Cloud Collisions
• X-ray Line Diagnostics of Ion Temperature at Cosmic-Ray Accelerating Collisionless Shocks
• Chemical diversity of gas in distant galaxies: The metal and dust enrichment and variations within absorbing galaxies
• HyGAL: Characterizing the Galactic ISM with observations of hydrides and other small molecules II. The absorption line survey with the IRAM 30 m telescope
• Galaxy Formation and Symbiotic Evolution with the Inter-Galactic Medium in the Age of ELT-ANDES
• Spatial metallicity variations of mono-temperature stellar populations revealed by early-type stars in LAMOST
• The Radcliffe Wave as traced by young open clusters: Stellar parameters, activity indicators, and abundances of solar-type members of eight young clusters
• Mapping the aliphatic hydrocarbon content of interstellar dust in the Galactic plane
• Geoastronomy: Rocky planets as the Lavosier-Lomonosov Bridge from the non-living to the living world
• Modelling of long gamma-ray burst host galaxies at cosmic noon from damped Lyman-α absorption statistics
• Constraining gas metal mixing strength in simulations using observations of the Milky Way's disc
• The effect of saturated thermal conduction on clouds in a hot plasma
• Discovery of a damped Ly$\alpha$ absorber originating in a spectacular interacting dwarf galaxy pair at $z=0.026$
• Velocity Dispersion and H$\alpha$ emission of Ionized Gas in Star-forming Regions
• On the origin of the Hercules group: I. chemical signatures indicating the outer bar origin
• Investigating chemical variations between interstellar gas clouds in the Solar neighbourhood
• Rapid Response Mode observations of GRB 160203A: Looking for fine-structure line variability at z=3.52
• Photometric Mapping of Carbonaceous/Siliceous Dust and Water Ice in the ISM with JWST: Applications to the Dense Sightlines
• First detections of CO absorption in the Magellanic Clouds and direct measurement of the CO-to-H${}_2$ ratio
• Families and Clusters of Diffuse Interstellar Bands: a Data-Driven Correlation Analysis
• Primordial helium-3 redux: The helium isotope ratio of the Orion nebula
• Connecting the dusty dots: dust depletion and extinction of local interstellar clouds