2004/01/05 by Steven V. Penton, John T. Stocke, J. Michael Shull · 14 citations
Physics and Astronomy · #Cosmology and Gravitation Theories #Galaxies: Formation, Evolution, Phenomena #Radio Astronomy Observations and Technology #astro-ph
paper · pdf · doi:10.1086/382877
published as Astrophys.J.Suppl.152:29,2004 · 71 pages, 6 tables, 26 EPS figures, to appear in ApJ Supplement
arxiv created 2004/01/05 · openalex publication_date 2004/04/19 · arxiv updated 2009/12/01 · openalex created_date 2016/06/24 · openalex updated_date 2026/07/31
We present Hubble Space Telescope ( HST ) Space Telescope Imaging Spectrograph (STIS) G140M spectra of 15 extragalactic targets, which we combine with GHRS/G160M data to examine the statistical properties of the low- z Lyα forest. With STIS, we detect 109 Lyα absorbers at significance level (SL) of ≥4 σ over 0.002 < z < 0.069, with a total redshift path length Δ z = 0.770. Our combined sample consists of 187 Lyα absorbers with SL ≥ 4 σ over Δ z = 1.157. We evaluate the physical properties of these Lyα absorbers and compare them to their high- z counterparts. Using two different models for Lyα forest absorbers, we determine that the warm, photoionized intergalactic medium contains 29% ± 4% of the total baryon inventory at z = 0 (assuming J 0 = 1.3 × 10 -23 ergs cm -2 s -1 Hz -1 sr -1 ). We derive the distribution in column density, N for 12.5 ≤ log ≤ 14.5, breaking to a flatter slope above log ≈ 14.5. As with the high equivalent width ( > 240 mÅ) absorbers, the number density of low- absorbers at z = 0 is well above the extrapolation of d / dz from z > 2. However, log = 1.40 ± 0.08 for > 240 mÅ is 25% below the value obtained by the HST QSO Key Project, a difference that may arise from line blending. The slowing of the number density evolution of high- Lyα clouds is not as great as previously measured, and the break to slower evolution may occur later than previously suggested ( z ∼ 1.0 rather than 1.6). We find a 7.2 σ excess in the two-point correlation function (TPCF) of Lyα absorbers for velocity separations Δ v ≤ 260 km s -1 , which is exclusively due to the higher column density clouds. From our previous result that higher column density Lyα clouds cluster more strongly with galaxies, this TPCF suggests a physical difference between the higher and lower column density clouds in our sample. The systematic error produced by cosmic variance on these results increases the total errors on derived quantities by ∼ .