The UCSD HIRES/Keck I Damped Lyα Abundance Database. II. The Implications

By J. Xavier Prochaska, A. Wolfe. 2001

172 citations recorded by the source corpus.

We present a comprehensive analysis of the damped Lyα (DLA) abundance database presented in the first paper of this series. This database provides a homogeneous set of abundance measurements for many elements including Si, Cr, Ni, Zn, Fe, Al, S, Co, O, and Ar from 38 DLA systems with zabs > 1.5. With little exception, these DLA systems exhibit very similar relative abundances. There is no significant correlation in X/Fe with [Fe/H] metallicity, and the dispersion in X/Fe is small at all metallicity. We search the database for trends indicative of dust depletion and in a few cases find strong evidence. Specifically, we identify a correlation between [Si/Ti] and [Zn/Fe] which is unambiguous evidence for depletion. Following Hou and colleagues, we present [X/Si] abundances against [Si/H] + log N(H ) and note trends of decreasing X/Si with increasing [Si/H] + log N(H ) which argue for dust depletion. Similarly, comparisons of [Si/Fe] and [Si/Cr] against [Si/H] indicate significant depletion at [Si/H] > -1 but suggest essentially dust-free damped systems at [Si/H] < -1.5 dex. We present a discussion on the nucleosynthetic history of the DLA systems by focusing on abundance patterns which are minimally affected by dust depletion. We find [Si/Fe] → 0.25 dex as [Zn/Fe] → 0 and that the [Si/Fe] values exhibit a plateau of ≈0.3 dex at [Si/H] < -1.5 dex. Together these trends indicate significant α-enrichment in the DLA systems at low metallicity, an interpretation further supported by the observed O/Fe, S/Fe, and Ar/Fe ratios. Comparing the relative abundances of the Fe peak elements, we identify important offsets from solar relative abundances for Cr, Ni, and Fe which suggest variations in nucleosynthesis along the Fe peak. Finally, the DLA systems exhibit a modest odd-even effect revealed by Si/Al, [Si/Al] ≈ 0.4 dex, which is significantly smaller than values observed in Galactic halo stars of comparable metallicity. These observations present strong evidence that the DLA systems and Galactic halo had different enrichment histories. To assess the impact of dust obscuration, we present estimates of the dust-to-gas ratios for the DLA sight lines and crudely calculate dust extinction corrections. The distribution of extinction corrections suggests that the effects of dust obscuration are minimal and that the population of "missing" damped systems has physical characteristics similar to the observed sample. We update our investigation on the chemical evolution of the early universe in neutral gas. The results are in good agreement with our previous work, but we emphasize two differences: (1) the unweighted and N(H I)-weighted [Fe/H] mean metallicities now have similar values at all epochs except z > 3.5, where small number statistics dominate the N(H I)-weighted mean; and (2) there is no evolution in the mean [Fe/H] metallicity from z = 1.7 to 3.5 but possibly a marked drop at higher redshift. We conclude with a general discussion on the physical nature of the DLA systems. We stress the uniformity of the DLA chemical abundances which indicates that the protogalaxies identified with DLA systems have very similar enrichment histories, i.e., a nearly constant relative contribution from Type Ia and Type II supernovae. The DLA systems also show constant relative abundances within a given system, which places strict constraints on the mixing timescales of the damped systems and may pose a great challenge to the protogalactic clump scenarios favored by hierarchical galaxy formation.

Subfields: Astronomy and Astrophysics

View Paper: https://www.semanticscholar.org/paper/dce42b5325b40a6fda5c5cda1ecca76f47249335

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In Astronomy and Astrophysics

1. M. Pettini
2. C. Steidel
3. A. Shapley
4. D. Erb
5. Naveen A. Reddy
6. R. Dav'e
7. P. Hopkins
8. L. Hernquist

Citations in the corpus

• Feedback and metal enrichment in cosmological smoothed particle hydrodynamics simulations ¿ I. A model for chemical enrichment (2005, background): “…1994; Mushotzky et al. 1996; Ettori et al. 2002; Tremonti et al. 2004; Lamareille et al. 2004) as well as at intermediate and high redshifts (e.g. Prochaska & Wolfe 2002; Adelberger ⋆ E-mail: cecilia@iafe.uba.ar (CS); patricia@iafe.uba.ar (PBT); swhite@mpa-garching.mpg.de (SDMW);…”
• Stellar sources of dust in the high-redshift Universe (2009, methodology): “Evidence for the presence of dust at high redshifts comes from observations of damped Lyα systems (Pettini et al. 1994; Prochaska & Wolfe 2002; Ledoux, Bergeron & Petitjean 2002) and from the detection of dust thermal emission from high redshift quasars (QSOs) selected from the Sloan Digital Sky…”
• The most metal-poor damped Lyα systems: insights into chemical evolution in the very metal-poor regime★ (2011, background): “The reason is that the most readily available O i absorption lines are almost always saturated, and the weakest lines are often blended with unrelated absorption in the Lyα forest (Prochaska & Wolfe 2002).”
• C II* Absorption in Damped Lyα Systems. I. Star Formation Rates in a Two-Phase Medium (2003, background): “Such stars emit FUV radiation (hν = 6 − 13.6 eV) that illuminates dust grains known to be present in the gas (Pei & Fall 1995; Prochaska & Wolfe 2002; hereafter PW02).”
• First detection of CO in a high-redshift damped Lyman-α system (2008, background): “The inferred metallicities relative to solar vary between [Zn/H] = −2.0 and 0 for 2 ≤ zabs ≤ 3 (e.g. Pettini et al. 1997; Prochaska & Wolfe 2002).”
• A UNIFIED REPRESENTATION OF GAS-PHASE ELEMENT DEPLETIONS IN THE INTERSTELLAR MEDIUM (2009, methodology): “Witt, A. N., Smith, R. K., & Dwek, E. 2001, ApJ, 550, L201 Wolfe, A. M., Gawiser, E., & Prochaska, J. X. 2005, ARA&A, 43, 861 Wolff, B., Koester, D., & Lallement, R. 1999, A&A, 346, 969 Wood, B. E., & Linsky, J. L. 1997, ApJ, 474, L39 Wood, B. E., Redfield, S., Linsky, J. L., & Sahu, M. S. 2002, ApJ”
• Oxygen, carbon and nitrogen evolution in galaxies (2002, background): “In fact, DLAs offer another important piece of information (Pettini et al. 1995; Prochaska & Wolfe 2002) as in this case it is possible to probe the very early phases of evolution of such systems.”
• Probing the Interstellar Medium near Star-forming Regions with Gamma-Ray Burst Afterglow Spectroscopy: Gas, Metals, and Dust (2007, background): “Similarly, the QSO-DLAs show a plateau of [Si/Fe] =+0.25dex values at low metallicity indicative of Type II enrichment (Prochaska & Wolfe 2002), and enhanced α/Fe ratios in “dust free” systems (Dessauges-Zavadsky et al. 2006).”
• Evidence for Solar Metallicities in Massive Star-forming Galaxies at z ≳ 2 (2004, background): “At much higher redshift, z > 2:5, most of the information about the abundances of galaxies has been derived from absorption lines in damped Ly systems (DLAs; e.g., Pettini et al. 1997; Prochaska & Wolfe 2002).”
• New Observations of the Interstellar Medium in the Lyman Break Galaxy MS 1512–cB58 (2001, background): “Second, and somewhat paradoxically, the enhancement of the -elements relative to Fe, expected at these low metallicities by analogy with metal-poor stars in the Milky Way, has proved very elusive to pin down in DLAs (Vladilo 1998; Pettini et al. 2000a; Prochaska & Wolfe 2002).”
• METALLICITY EVOLUTION OF DAMPED Lyα SYSTEMS OUT TO z ∼ 5 (2012, methodology): “While Si has nearly twice the mass density of S, it is a mildly refractory element and its gas-phase measurement may under- estimate the total metal abundance (Prochaska & Wolfe 2002; Vladilo et al. 2011).”
• Molecular hydrogen in high-redshift Damped Lyman-alpha systems: The VLT/UVES database (2008, background): “Our understanding of DLAs is mainly based on the study of low-ionisation metal absorptions (e.g., Prochaska & Wolfe 2002) but also high-ionisation species (Lu et al. 1996; Wolfe & Prochaska 2000; Fox et al. 2007a,b) and, in a few cases, molecular absorptions (e.g., Ledoux et al. 2003).”
• The Very Large Telescope Ultraviolet and Visible Echelle Spectrograph survey for molecular hydrogen in high‐redshift damped Lyman α systems (2003, unknown): “However, from this alone, it was unclear whether this trend is a consequence of dust depletion effects or peculiar nucleosynthesis history of zinc (Prochaska & Wolfe 2002).”