The Age-Metallicity Relation of the Universe in Neutral Gas: The First 100 Damped Lyα Systems

By J. Xavier Prochaska, E. Gawiser, A. Wolfe, S. Castro, S. George Djorgovski. 2003

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We discuss accurate metallicity measurements for 125 damped Lyα (DLA) systems at 0.5 < z < 5, including ≈50 new measurements from our recently published Echellette Spectrograph and Imager surveys. This data set is analyzed to determine the age-metallicity relation of neutral gas in the universe. Contrary to previous analyses, this sample shows statistically significant evolution in the cosmic mean metallicity. The best linear fit for metallicity evolution is -0.26 ± 0.07 dex per unit redshift. The DLA systems continue to maintain a floor in metallicity of ≈1/700 solar, independent of observational effects. This metallicity threshold limits the prevalence of primordial gas in high-redshift galaxies and stresses the correspondence between damped systems and star formation. Finally, we comment on an apparent "missing metals problem:" the mean metallicity of the damped systems is ≈10 times lower than the value expected from their inferred star formation history. This problem is evident in current theoretical treatments of galaxy formation and may indicate a serious flaw in our understanding of the interplay between star formation and metal enrichment.

Subfields: Astronomy and Astrophysics

View Paper: https://www.semanticscholar.org/paper/c2aadb59fcf7bee7ec845bc3fd74d9d9d360e272

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The big problems in star formation: The star formation rate, stellar clustering, and the initial mass function (2014, background): “…the stellar population, and since this is dominated by young stars, it is a reasonable proxy for the star formation rate. ted – roughly 20% of Solar for the SMC (Bolatto et al. 2011), and likely between 1% and 10% of Solar for DLAs and LBG outskirts1 (Prochaska et al. 2003; Rafelski et al. 2012).”
Damped Lyman α systems in galaxy formation simulations (2008, methodology): “These are derived from the Prochaska et al. (2003) sample described inSection 4.2.2, restricted to2 < z < 4.”
THE BIMODAL METALLICITY DISTRIBUTION OF THE COOL CIRCUMGALACTIC MEDIUM AT z ≲ 1 (2013, background): “5 (e.g., Prochaska et al. 2003; Battisti et al. 2012; Rafelski et al. 2012).”
The physics of the intergalactic medium (2007, background): “They are the dominant reservoir of neutral hydrogen at high redshifts (z > 3) (Jorgenson et al., 2006; Prochaska et al., 2005), 2. with the cosmic gas mass density ΩDLAg decreasing and metallicity increasing with cosmic time (Prochaska et al., 2003).”
METALLICITY EVOLUTION OF DAMPED Lyα SYSTEMS OUT TO z ∼ 5 (2012, methodology): “This yields an 6.7σ detection in the evolution of〈Z〉, which is a significant improvement over the previous∼ 3σ detections by Prochaska et al. (2003b), Kulkarni et al. (2005), Kulkarni et al. (2007), and Kulkarni et al. (2010).”
Absorption-line systems in simulated galaxies fed by cold streams (2011, background): “DLA gas inside the main galaxy and satellites is significantly enriched, with values close to 1/10 solar (in reasonable agreement with DLA observations; e.g. Prochaska et al. 2003).”
Simulations of Cosmic Chemical Enrichment (2006, background): “The metallicities of DLA systems (error bars, Prochaska et al. 2003; triangles, Kulkarni et al. 2005) are comparable with our galaxies, suggesting an identification of DLAs with dwarf galaxies or the outskirts of massive galaxies.”
Mg II Absorption Systems in Sloan Digital Sky Survey QSO Spectra (2005, background): “Furthermore, unsaturated low-ionization metal lines associated with strong Mg ii systems can be used to deduce neutral phase metal abundances (Pettini et al. 1999; Nestor et al. 2003; Prochaska et al. 2003).”
Implications for Cosmic Reionization from the Optical Afterglow Spectrum of the Gamma-Ray Burst 050904 at z = 6.3 (2005, background): “However,such a low m etallicity isnotobserved in any Q SO -DLAsatz 1{5,though thereisnom easurem entsofQ SO -DLA m etallicityatz> 6 (Prochaska et al. 2003).”
Damped Lyα Systems at z < 1.65: The Expanded Sloan Digital Sky Survey Hubble Space Telescope Sample (2006, background): “For example, there is now clear evidence that the neutral gas phase element abundances are increasing from high to low redshift (e.g., Prochaska et al. 2003a; Rao et al. 2005).”
Galaxy bimodality due to cold flows and shock heating (2004, background): “Observations in the range z = 1−4 (Prochaska et al. 2003) can be fitted on average by eq.”
Probing the Interstellar Medium near Star-forming Regions with Gamma-Ray Burst Afterglow Spectroscopy: Gas, Metals, and Dust (2007, methodology): “The echellette observations, in particular, have too poor data quality to generally achieve better than 0.1 dex precision (Prochaska et al. 2003) and are not included.”
The enrichment of the intergalactic medium with adiabatic feedback – I. Metal cooling and metal diffusion (2009, methodology): “We computed the mean metallicities of the halo gas and the ISM and compared it with the metallicity evolution of the DLAs and sub-DLAs from Prochaska et al. (2003) (triangle symbols in the bottom right panel of Figure 6).”
Chemical enrichment in cosmological, smoothed particle hydrodynamics simulations (2009, methodology): “We compare our predictions for overdense, cold non-starforming gas to the observations of damped Lyα (DLA) systems of Prochaska et al. (2003) and find excellent agreement.”
Cosmological simulations of intergalactic medium enrichment from galactic outflows (2006, background): “This enrichment level and evolution is similar to that seen for damped Lyα systems (Prochaska et al. 2003), which are expected to arise in condensed gas.”
FORMATION OF THE FIRST NUCLEAR CLUSTERS AND MASSIVE BLACK HOLES AT HIGH REDSHIFT (2008, methodology): “The cosmic metallicity history (MEH) has been investigated both from an observational and a theoretical prospective (Scannapieco et al. 2003, Tornatore et al. 2006, Savaglio 2006, Savaglio et al. 2005, Prochaska et al. 2003, Prochaska et al. 2007, Kulkarni et al. 2005, Li 2007).”
The SDSS Damped Lyα Survey: Data Release 3 (2005, background): “In general, we focused on the strongest low-ion transitions observed in the damped Lyα systems (e.g. Prochaska et al. 2003a): Si IIλ1260, 1304, 1526, O Iλ1302, C IIλ1334, Al IIλ1670, and Fe IIλ1608,2382,2600.”
Reconciling the local galaxy population with damped Lyman α cross-sections and metal abundances (2005, methodology): “For all measurements of metallicity a slope between−0.25 and −0.3 dex per unit redshift can be seen, in agreement with the findings of Prochaska et al. (2003) and Kulkarni et al. (2005), on whose compilations of data this figure is based.”