2011/05/03 by Joseph Ribaudo, Nicolas Lehner, J. Christopher Howk · 1 citation
Physics and Astronomy · #Astronomy #Astronomy and Astrophysical Research #Astrophysical Phenomena and Observations #Astrophysics #Galaxies: Formation, Evolution, Phenomena #Galaxy #Hubble space telescope #Intergalactic medium #Lyman limit #Physics #Quasar #Redshift #Space Telescope Imaging Spectrograph #Spectral density #astro-ph.CO
paper · pdf · doi:10.1088/0004-637x/736/1/42
Accepted by ApJ
arxiv created 2011/05/03 · openalex publication_date 2011/07/05 · arxiv updated 2015/05/28 · openalex created_date 2016/06/24 · openalex updated_date 2026/08/05
We present a survey for optically thick Lyman limit absorbers at z < 2.6 using archival Hubble Space Telescope observations with the Faint Object Spectrograph and Space Telescope Imaging Spectrograph. We identify 206 Lyman limit systems (LLSs), increasing the number of cataloged LLSs at z < 2.6 by a factor of ∼10. We compile a statistical sample of 50 τ LLS ⩾ 2 LLSs drawn from 249 QSO sight lines that avoid known targeting biases. The incidence of such LLSs per unit redshift, l ( z ) = dn / dz , at these redshifts is well described by a single power law, l ( z )∝(1 + z ) γ , with γ = 1.33 ± 0.61 at z < 2.6, or with γ = 1.83 ± 0.21 over the redshift range 0.2 ⩽ z ⩽ 4.9. The incidence of LLSs per absorption distance, l ( X ), decreases by a factor of ∼1.5 over the ∼0.6 Gyr from z = 4.9 to 3.5; l ( X ) evolves much more slowly at low redshifts, decreasing by a similar factor over the ∼8 Gyr from z = 2.6 to 0.25. We show that the column density distribution function, f ( N H i ), at low redshift is not well fitted by a single power-law index ( f ( N H i ) ∝ N −β H i ) over the column density range 13 ⩽ log N H i ⩽ 22 or log N H i ⩾ 17.2. While low- and high-redshift f ( N H i ) distributions are consistent for log N H i >19.0, there is some evidence that f ( N H i ) evolves with z for log N H i ≲ 17.7, possibly due to the evolution of the UV background and galactic feedback. Assuming LLSs are associated with individual galaxies, we show that the physical cross section of the optically thick envelopes of galaxies decreased by a factor of ∼9 from z ∼ 5 to 2 and has remained relatively constant since that time. We argue that a significant fraction of the observed population of LLSs arises in the circumgalactic gas of sub- L * galaxies.