Chandra ACIS-S Observations of Three Quasars with Low-Redshift Damped Ly-alpha Absorption: Constraints on the Cosmic Neutral-Gas-Phase Metallicity at Redshift z \approx 0.4

Abstract

Chandra X-Ray Observatory (CXO) ACIS-S spectra of three quasars which lie behind three foreground damped Lyman alpha (DLA) absorbers are analyzed in order to attempt to determine the amount of photoelectric absorption due to metals present in their x-ray spectra. These absorbers are the three largest neutral hydrogen column density absorption-line systems known at low redshift (0.313 \le z_abs \le 0.524). They have HI column densities which lie between 3E21 and 5E21 atoms/cm^2. At these redshifts the amount of photoelectric absorption at x-ray energies is primarily an indicator of the oxygen abundance. Since the column densities of these systems are so high, one would expect accurate metallicity measurements of them to yield a robust estimate of the column-density-weighted cosmic neutral-gas-phase metallicity at z \approx 0.4. We consider cases where the DLA gas has solar element abundance ratios and ones with the alpha-group element abundance ratios enhanced. For the adopted assumptions, the column-density-weighted cosmic neutral-gas-phase metallicity of the non-enhanced elements (e.g. Zn) at z \approx 0.4 likely lies in the range \approx 0.04-0.38 Z_solar.

arXiv comment15 pages, 6 figures. Accepted for publication in the Astrophysical Journal

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• Abundance Profiles and Kinematics of Damped Lyman-alpha Absorbing Galaxies at z < 0.65
• Low-Redshift Damped Lyman Alpha Galaxies Toward the Quasars B2 0827+243, PKS 0952+179, PKS 1127-145, and PKS 1629+120
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• Dust and Diffuse Interstellar Bands in the z_a = 0.524 Absorption System toward AO 0235+164
• Very different X-ray to optical column density ratios in gamma-ray burst afterglows: ionisation in GRB environments
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• X-ray emission from the blazar AO 0235+16: the XMM-Newton and Chandra point of view
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