The cosmic evolution of the metallicity distribution of ionized gas traced by Lyman limit systems
- Center of Astrophysics, Department of Physics, University of Notre Dame, 225 Nieuwland Science Hall, Notre Dame, IN 46556 (United States)
- Department of Chemistry and Physics, Saint Michael’s College, One Winooski Park, Colchester, VT 05439 (United States)
- Department of Astronomy and Astrophysics, University of California, 1156 High Street, Santa Cruz, CA 95064 (United States)
- Institute for Computational Cosmology and Centre for Extragalactic Astronomy, Department of Physics, Durham University, South Road, Durham, DH1 3LE (United Kingdom)
We present the first results from our KODIAQ Z survey aimed at determining the metallicity distribution and physical properties of the z≳2 partial and full Lyman limit systems (pLLSs and LLSs; 16.2⩽logN{sub HI}<19), which are probed of the interface regions between the intergalactic medium (IGM) and galaxies. We study 31 H i-selected pLLSs and LLSs at 2.3<3.3 observed with Keck/HIRES in absorption against background QSOs. We compare the column densities of metal ions to H i and use photoionization models to assess the metallicity. The metallicity distribution of the pLLSs/LLSs at 2.3<3.3 is consistent with a unimodal distribution peaking at [X/H]≃−2. The metallicity distribution of these absorbers therefore evolves markedly with z since at z≲1 it is bimodal with peaks at [X/H]≃−1.8 and −0.3. There is a substantial fraction (25%–41%) of pLLSs/LLSs with metallicities well below those of damped Lyα absorbers (DLAs) at any studied z from z≲1 to z∼2–4, implying reservoirs of metal-poor, cool, dense gas in the IGM/galaxy interface at all z. However, the gas probed by pLLSs and LLSs is rarely pristine, with a fraction of 3%–18% for pLLSs/LLSs with [X/H]⩽−3. We find C/α enhancement in several pLLSs and LLSs in the metallicity range −2≲[X/H]≲−0.5, where C/α is 2–5 times larger than observed in Galactic metal-poor stars or high-redshift DLAs at similar metallicities. This is likely caused by preferential ejection of carbon from metal-poor galaxies into their surroundings.
- OSTI ID:
- 22869626
- Journal Information:
- Astrophysical Journal, Vol. 833, Issue 2; Other Information: Country of input: International Atomic Energy Agency (IAEA); ISSN 0004-637X
- Country of Publication:
- United States
- Language:
- English
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