An excess of damped Lyman α galaxies near quasi-stellar objects |
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Authors: | David M. Russell Sara L. Ellison Chris R. Benn |
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Affiliation: | Isaac Newton Group, Apartado 321, E-38700, Santa Cruz de La Palma, Spain;School of Physics &Astronomy, University of Southampton, Highfield, Southampton SO17 1BJ;Department of Physics &Astronomy, University of Victoria, 3800 Finnerty Road, Victoria, BC V8P 1A1, Canada |
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Abstract: | We present a sample of 33 damped Lyman α systems (DLAs) discovered in the Sloan Digital Sky Survey (SDSS) whose absorption redshifts ( z abs) are within 6000 km s−1 of the quasi-stellar object's (QSO) systemic redshift ( z sys). Our sample is based on 731 2.5 < z sys < 4.5 non-broad absorption line (non-BAL) QSOs from Data Release 3 (DR3) of the SDSS. We estimate that our search is ≈100 per cent complete for absorbers with N (H i ) ≥ 2 × 1020 cm−2 . The derived number density of DLAs per unit redshift, n ( z ), within Δ v < 6000 km s−1 is higher (3.5σ significance) by almost a factor of 2 than that of intervening absorbers observed in the SDSS DR3, i.e. there is evidence for an overdensity of galaxies near the QSOs. This provides a physical motivation for excluding DLAs at small velocity separations in surveys of intervening 'field' DLAs. In addition, we find that the overdensity of proximate DLAs is independent of the radio-loudness of the QSO, consistent with the environments of radio-loud and radio-quiet QSOs being similar. |
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Keywords: | quasars: emission lines quasars: general early Universe radio continuum: galaxies |
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