Metal-Poor, Cool Gas in the Circumgalactic Medium of a z = 2.4 Star-Forming Galaxy: Direct Evidence for Cold Accretion?

Abstract

In our current galaxy formation paradigm, high-redshift galaxies are predominantly fuelled by accretion of cool, metal-poor gas from the intergalactic medium. Hydrodynamical simulations predict that this material should be observable in absorption against background sightlines within a galaxy's virial radius, as optically thick Lyman-limit systems (LLSs) with low metallicities. Here we report the discovery of exactly such a strong metal-poor absorber at an impact parameter R_perp = 58 kpc from a star-forming galaxy at z = 2.44. Besides strong neutral hydrogen [N(HI) = 10^(19.50 +/- 0.16) cm^-2] we detect neutral deuterium and oxygen, allowing a precise measurement of the metallicity: log10(Z / Zsolar) = -2.0 +/- 0.17, or (7-15) x 10^-3 solar. Furthermore, the narrow deuterium linewidth requires a cool temperature < 20,000 K. Given the striking similarities between this system and the predictions of simulations, we argue that it represents the direct detection of a high redshift cold-accretion stream. The low-metallicity gas cloud is a single component of an absorption system exhibiting a complex velocity, ionization, and enrichment structure. Two other components have metallicities > 0.1 solar, ten times larger than the metal-poor component. We conclude that the photoionized circumgalactic medium (CGM) of this galaxy is highly inhomogeneous: the majority of the gas is in a cool, metal-poor and predominantly neutral phase, but the majority of the metals are in a highly-ionized phase exhibiting weak neutral hydrogen absorption but strong metal absorption. If such inhomogeneity is common, then high-resolution spectra and detailed ionization modelling are critical to accurately appraise the distribution of metals in the high-redshift CGM.

Changed to the final version accepted by ApJL; main results and conclusions are unchanged. Data and code used in this analysis are available at https://github.com/nhmc/z2.4CGM, and changes with respect to the previous version are summarised here: https://github.com/nhmc/z2.4CGM/blob/master/CHANGES

References in corpus (7)

• Cold streams in early massive hot haloes as the main mode of galaxy formation
• The Mass-Metallicity Relation at z~2
• A Unified Representation of Gas-Phase Element Depletions in the Interstellar Medium
• H-alpha Observations of a Large Sample of Galaxies at z~2: Implications for Star Formation in High Redshift Galaxies
• Moving mesh cosmology: tracing cosmological gas accretion
• The VLT LBG Redshift Survey - III. The clustering and dynamics of Lyman-break galaxies at z ~ 3
• Multiphase Plasma in Sub-Damped Lyman Alpha Systems: A Hidden Metal Reservoir

Cited by in corpus (65)

• The COS-Halos Survey: Rationale, Design, and A Census of Circumgalactic Neutral Hydrogen
• Four phases of angular-momentum buildup in high-z galaxies: from cosmic-web streams through an extended ring to disc and bulge
• A Characteristic Scale for Cold Gas
• Magnetized Gas Clouds can Survive Acceleration by a Hot Wind
• Star formation sustained by gas accretion
• Neutral hydrogen in galaxy halos at the peak of the cosmic star formation history
• Metal-enriched, sub-kiloparsec gas clumps in the circumgalactic medium of a faint z = 2.5 galaxy
• Quasars Probing Quasars VII. The Pinnacle of the Cool Circumgalactic Medium Surrounds Massive z~2 Galaxies
• Galactic and Circumgalactic OVI and its Impact on the Cosmological Metal and Baryon Budgets at 2<z<3.5
• Instability of Supersonic Cold Streams Feeding Galaxies IV: Survival of Radiatively Cooling Streams
• Snap, Crackle, Pop: sub-grid supernova feedback in AMR simulations of disk galaxies
• High Angular Momentum Halo Gas: a Feedback and Code-Independent Prediction of LCDM
• The Azimuthal Dependence of Outflows and Accretion Detected Using OVI Absorption
• The ESO UVES Advanced Data Products Quasar Sample - VI. Sub-Damped Lyman-$\alpha$ Metallicity Measurements and the Circum-Galactic Medium
• Project AMIGA: The Circumgalactic Medium of Andromeda
• MUSE searches for galaxies near very metal-poor gas clouds at z~3: new constraints for cold accretion models
• The physics of gas phase metallicity gradients in galaxies
• The Cosmic Evolution of the Metallicity Distribution of Ionized Gas Traced by Lyman Limit Systems
• Circumgalactic Mg II Emission from an Isotropic Starburst Galaxy Outflow Mapped by KCWI
• Quasars Probing Quasars VIII. The Physical Properties of the Cool Circumgalactic Medium Surrounding z ~ 2-3 Massive Galaxies Hosting Quasars
• Probing the Circumgalactic Medium at High-Redshift Using Composite BOSS Spectra of Strong Lyman-alpha Forest Absorbers
• NIHAO VIII: Circum-galactic medium and outflows - The puzzles of HI and OVI gas distributions
• Tracing Outflowing Metals in Simulations of Dwarf and Spiral Galaxies
• Probing the Cool Interstellar and Circumgalactic Gas of Three Massive Lensing Galaxies at z=0.4-0.7
• Dissecting the Gaseous Halos of z~2 Damped Ly$\alpha$ Systems with Close Quasar Pairs
• The Stacked Lyman-Alpha Emission Profile from the Circum-Galactic Medium of z~2 Quasars
• Relationship between the Metallicity of the Circumgalactic Medium and Galaxy Orientation
• Galaxies Probing Galaxies in PRIMUS - I. Sample, Spectroscopy, and Characteristics of the z~0.5 MgII-Absorbing Circumgalactic Medium
• The COS CGM Compendium. III: Metallicity and Physical Properties of the Cool Circumgalactic Medium at z<1
• Cold-Mode Accretion: Driving the Fundamental Mass-Metallicity Relation at z~2
• A Deep Narrowband Imaging Search for CIV and He II Emission from Ly$\alpha$ Blobs
• The COS CGM Compendium (CCC). I: Survey Design and Initial Results
• The RESOLVE Survey Atomic Gas Census and Environmental Influences on Galaxy Gas Reservoirs
• The Relationship Between Galaxy ISM and Circumgalactic Gas Metallicities
• The High-Ion Content and Kinematics of Low-Redshift Lyman Limit Systems
• The Role of Cold Flows and Reservoirs in Galaxy Formation With Strong Feedback
• The Incidence of Low-Metallicity Lyman-Limit Systems at z~3.5: Implications for the Cold-Flow Hypothesis of Baryonic Accretion
• Galaxies Probing Galaxies in PRIMUS - II. The Coherence Scale of the Cool Circumgalactic Medium
• From large-scale environment to CGM angular momentum to star forming activities -- I: star-forming galaxies
• MAGIICAT IV. Kinematics of the Circumgalactic Medium and Evidence for Quiescent Evolution Around Red Galaxies
• Lyman Alpha and MgII as Probes of Galaxies and their Environments
• Simba: The average properties of the circumgalactic medium of $2\le z\le 3$ quasars are determined primarily by stellar feedback
• The CGM at Cosmic Noon with KCWI: Outflows from a Star-forming Galaxy at z=2.071
• A Fundamental Test for Galaxy Formation Models: Matching the Lyman-$\alpha$ Absorption Profiles of Galactic Halos over Three Decades in Distance
• An Introduction to Gas Accretion onto Galaxies
• GASP. VII. Gas accretion onto an isolated galaxy
• Gas inflow and outflow in an interacting high-redshift galaxy: The remarkable host environment of GRB 080810 at $z=3.35$
• The Bimodal Absorption System Imaging Campaign (BASIC) I. A Dual Population of Low-metallicity Absorbers at z $<1$
• Predominantly Low Metallicities Measured in a Stratified Sample of Lyman Limit Systems at z=3.7
• Spatially-resolved chemodynamics of the starburst dwarf galaxy CGCG 007-025: Evidence for recent accretion of metal-poor gas
• Gas Accretion in Star-Forming Galaxies
• Metal enrichment in a semi-analytical model, fundamental scaling relations, and the case of Milky Way galaxies
• A Long Stream of Metal-Poor Cool Gas around a Massive Starburst Galaxy at z = 2.67
• Numerical Simulations of a Shock-Filament Interaction
• Gas Accretion and Angular Momentum
• VLT/UVES observations of peculiar alpha abundances in a sub-DLA at z ~ 1.8 towards the quasar B1101-26
• Physical Conditions of Five O VI Absorption Systems Towards PG $1522+101$
• The Circumgalactic Medium in Massive Halos
• Probing IGM accretion onto faint Lyα emitters at z~2.8
• Gas Accretion via Lyman Limit Systems
• Cold stream stability during minor mergers
• Low Mass Group Environments have no Substantial Impact on the Circumgalactic Medium Metallicity
• Evolution of cold streams in hot gaseous halos
• On the Metallicities and Kinematics of the Circumgalactic Media of Damped Ly$\alpha$ Systems at $z\sim 2.5$
• You Are What You Eat: The Circumgalactic Medium Around BreakBRD Galaxies has Low Mass and Angular Momentum