MgiiAbsorber Number Density atz ≃ 0.05: Implications for ΩDLAEvolution
Citations Over TimeTop 12% of 2001 papers
Abstract
An unbiased sample of 147 quasar/AGN spectra, obtained with the Faint Object Spectrograph on board the Hubble Space Telescope, has been searched for intervening Mgii λλ2796,2803 absorbers over the redshift range 0 < z ≤ 0.15. The total redshift path searched is 18.8, with the survey being 80 % complete to a 5 σ rest–frame equivalent width, Wr(2796), of 0.6 ˚A and 20 % complete to Wr(2796) = 0.3 ˚A. Main results of this work are the following. (1) Four systems were found, with a mean redshift of 〈z 〉 = 0.06, yielding a redshift number density dN/dz = 0.22 +0.12 −0.09 for absorbers with Wr(2796) ≥ 0.6 ˚A. This is consistent with the value expected if these systems do not evolve from higher redshifts (z = 2.2). (2) No systems with Wr(2796) < 0.6 ˚A were found. Based upon no evolution expectations and accounting for the survey completeness, it is a 2 σ result to have a null detection of smaller Wr(2796) systems. If this implies a turnover in the low Wr(2796) region of the equivalent width distribution at z ∼ 0, then there is at least a 25 % reduction in the average galaxy gas cross section from z ≤ 0.2 galaxies.
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