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The Magellan uniform survey of damped Lyman α systems - I. Cosmic metallicity evolution

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posted on 2024-07-26, 14:02 authored by R. A. Jorgenson, Michael MurphyMichael Murphy, R. Thompson
We present the chemical abundance measurements of the first large, medium-resolution, uniformly selected damped Lyman α system (DLA) survey. The sample contains 99 DLAs towards 89 quasars selected from the SDSS DR5DLA sample in a uniform way. We analyse the metallicities and kinematic diagnostics, including the velocity width of 90 per cent of the optical depth,δν90, and the equivalent widths of the Si II λ1526 (Wλ1526), CIV λ1548 and MgII λ2796 transitions. To avoid strong line-saturation effects on the metallicities measured in medium-resolution spectra (FWHM ~ 71 km s-1), we derived metallicities from metal transitions which absorbed at most 35 per cent of the quasarcontinuum flux. We find the evolution in cosmic mean metallicity of the sample, (Z) = (-0.04 +/- 0.13)z - (1.06 +/- 0.36), consistent with no evolution overthe redshift range z ~ [2.2, 4.4], but note that the majority of our samplefalls at z ~ [2.2, 3.5]. The apparent lack of metallicity evolution with redshift is also seen in a lack of evolution in the median δν90 and Wλ1526 values. While this result may seem to conflict with other large surveys that have detected significant metallicity evolution,such as Rafelski et al. who found (Z) = (-0.22 +/- 0.03)z - (0.65 +/- 0.09) over z ~ [0, 5], several tests show that these surveys are not inconsistent with our new result. However, over the smaller redshift range covered by our uniformly selected sample, the true evolution of the cosmic mean metallicity in DLAs may be somewhat flatter than the Rafelski et al. estimate.

Funding

Galaxy formation and femtosecond frequency combs

Australian Research Council

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Pristine fuel for early galaxies

Australian Research Council

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PDF (Published version)

ISSN

0035-8711

Journal title

Monthly Notices of the Royal Astronomical Society

Volume

435

Issue

1

Pagination

19 pp

Publisher

Oxford University Press

Copyright statement

Copyright © 2013 The authors. Published by Oxford University Press on behalf of the Royal Astronomical Society. The published version is reproduced in accordance with the copyright policy of the journal.

Language

eng

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