## Abstract

We present results for Lyα forest and metal absorbers from ∼7 km s^{-1} resolution Space Telescope Imaging Spectrograph data for QSO PKS 0405-123 (z = 0.574). We analyze strong and weak samples of Lyα forest lines, containing 60 absorbers with column density log N_{H1} ≥ 13.3 over 0.002 < z < 0.423 and 44 with log N_{H1} ≥ 13.1 over 0.020 < z < 0.234, respectively. Seven absorbers contain metals, all with associated O VI and often offset in velocity from Lyα. The strong and weak Doppler parameter distributions have 〈b〉 = 41 ± 22 and 44 ± 21 km s^{-1}, respectively. Simulated spectra suggest that line blending and signal-to-noise ratio effects inflate b. For absorbers with 13.1 < log N_{HI}, < 14.0, we find a redshift overdensity of ∼0.2-0.3 dex at 0.127 < z < 0.234, which we attribute to cosmic variance. There is a void in the strong sample at 0.0320 < z < 0.0814 with probability of random occurrence P < 0.0004. We detect Lyα-Lyα clustering in our sample on a scale of Δ_{v} ≤ 250 km s ^{-1} for log N_{HI} ≥ 13.3, consistent with a numerical model of structure evolution. We detect velocity correlations of up to 250 km s^{-1} between Lya absorbers and 39 galaxies at z < 0.43 out to a transverse distance of 1.6 h_{70}^{-1} local frame Mpc. The Lyα-galaxy two-point correlation function is significant out to Δ_{v} < 250 km s^{-1} and grows with minimum H I column density. The strongest signal occurs for log N_{HI} ≳ 13.5-14.0 absorbers and is similar to the galaxy-galaxy correlation, implying that such Lyα absorbers have masses log(M/M_{Ȯ}) = 11.3 _{-0.6}^{+1.0}. We find a correlation between local galaxy counts and local summed H I column density, with peak significance on scales of 4000-6000 km s^{-1} and probability of random occurrence P = 0.0009. Finally, we present column densities for a number of Galactic species.

Original language | English (US) |
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Pages (from-to) | 631-653 |

Number of pages | 23 |

Journal | Astrophysical Journal |

Volume | 636 |

Issue number | 2 I |

DOIs | |

State | Published - Jan 10 2006 |

Externally published | Yes |

## Keywords

- Cosmology: observations
- Intergalactic medium
- Quasars: absorption lines

## ASJC Scopus subject areas

- Astronomy and Astrophysics
- Space and Planetary Science