2006ApJ...636..631W

We present results for Lyα forest and metal absorbers from ∼7 km/s 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 logN_HI_≥13.3 over 0.002<z<0.423 and 44 with logN_HI_≥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≥47±22 and 44±21 km/s, respectively. Simulated spectra suggest that line blending and signal-to-noise ratio effects inflate b. For absorbers with 13.1<logN_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 Δv≤250 km/s for logN_HI_≥13.3, consistent with a numerical model of structure evolution. We detect velocity correlations of up to 250 km/s between Lyα absorbers and 39 galaxies at z<0.43 out to a transverse distance of 1.6 h^–1₇₀local frame Mpc. The Lyα-galaxy two-point correlation function is significant out to Δv<250 km/s and grows with minimum H I column density. The strongest signal occurs for logN_HI_≳13.5-14.0 absorbers and is similar to the galaxy-galaxy correlation, implying that such Lyα absorbers have masses log(M/M_☉)=11.3^+1.0_–0.6. 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 and probability of random occurrence P=0.0009. Finally, we present column densities for a number of Galactic species.