METALLICITY EVOLUTION OF DAMPED Lyα SYSTEMS OUT TO z ∼ 5

By M. Rafelski, A. Wolfe, J. Xavier Prochaska, M. Neeleman, A. Mendez. 2012

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We present chemical abundance measurements for 47 damped Lyα (DLA) systems, 30 at z > 4, observed with the Echellette Spectrograph and Imager and the High Resolution Echelle Spectrometer on the Keck telescopes. H i column densities of the DLAs are measured with Voigt profile fits to the Lyα profiles, and we find an increased number of false DLA identifications with Sloan Digital Sky Survey at z > 4 due to the increased density of the Lyα forest. Ionic column densities are determined using the apparent optical depth method, and we combine our new metallicity measurements with 195 from previous surveys to determine the evolution of the cosmic metallicity of neutral gas. We find the metallicity of DLAs decreases with increasing redshift, improving the significance of the trend and extending it to higher redshifts, with a linear fit of −0.22 ± 0.03 dex per unit redshift from z = 0.09–5.06. The metallicity “floor” of ≈1/600 solar continues out to z ∼ 5, despite our sensitivity for finding DLAs with much lower metallicities. However, this floor is not statistically different from a steep tail to the distribution. We also find that the intrinsic scatter of metallicity among DLAs of ∼0.5 dex continues out to z ∼ 5. In addition, the metallicity distribution and the α/Fe ratios of z > 2 DLAs are consistent with being drawn from the same parent population with those of halo stars. It is therefore possible that the halo stars in the Milky Way formed out of gas that commonly exhibits DLA absorption at z > 2.

Subfields: Astronomy and Astrophysics, Instrumentation

View Paper: https://www.semanticscholar.org/paper/0668cce38b0f5613d2b9ef267beec246fdbc7215

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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).”
Column density distribution and cosmological mass density of neutral gas: Sloan Digital Sky Survey-III Data Release 9 (2012, background): “We set the upper limit because the increasing density of the Ly-α forest can introduce a significant fraction of false DLA identifications owing to strong blending of the Ly-α forest lines at the SDSS resolution (Rafelski et al. 2012).”
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).”
Merging black hole binaries with the SEVN code (2018, result): “This formula comes from abundance measurements of a large sample of high-redshift damped Lyα systems (Rafelski et al. 2012), but re-scaled to have Z(z = 0) = Z , consistent with the Sloan Digital Sky Survey data (Gallazzi et al. 2008).”
Star formation sustained by gas accretion (2014, background): “From 0 < z < 5, the relationship has a slope of -0.2 dex per unit z, a large scatter (±1 dex at a given z), and a lower limit that extends at least to Z /3000 (Rafelski et al. 2012, 2014; Cooke et al. 2011b).”
De re metallica: the cosmic chemical evolution of galaxies (2018, background): “…2015a; Fumagalli, 2014; Pettini et al., 2008; Henry & Prochaska, 2007; Dessauges-Zavadsky et al., 2006; Wolfe et al., 2005; Prochaska et al., 2003a; Rafelski et al., 2012; Neeleman et al., 2013; Jorgenson et al., 2013; Berg et al., 2016a), although they probe a broad range of environments, whose…”
The progenitors of compact-object binaries: impact of metallicity, common envelope and natal kicks (2018, methodology): “In model 2 we assume that all stars formed in a given redshift bin ∆z have the same metallicity, but we calculate this metallicity as logZ(z)/Z = −0.19z if z ≤ 1.5 and logZ(z)/Z =−0.22z if z > 1.5, which corresponds to rescaling the formula by Rafelski et al. (2012), to obtain Z(z = 0) = Z .”
The effect of the metallicity-specific star formation history on double compact object mergers (2019, result): “…Section 6 that Z0 = 0.035, α = −0.23, and σ = 0.39 yield a good match to gravitational-wave observations when coupled with our other assumptions; this preferred model has a similar shape to the metallicity distribution inferred by Rafelski et al. (2012) from measurements of damped Lyman α galaxies.”
The Neutral Hydrogen Cosmological Mass Density at z = 5 (2015, methodology): “For example, Rafelski et al. (2012, 2014) find a misidentification rate of 26% for DLA candidates from SDSS DR5 at z > 4, and of 97% for candidates from DR9 at z > 4.7.”