THE LOCAL Lyα FOREST. II. DISTRIBUTION OF H l ABSORBERS, DOPPLER WIDTHS, AND BARYON CONTENT

摘要

In Paper I of this series we described observations of l5 extragalactic targets taken with the Hubble Space Telescope+GHRS +Gl60M grating for studies of the low-z Lyα forest. We reported the detection of 1ll Lyα absorbers at significance level (SL) ≥3 σ, 8l with SL ≤ 4 σ, in the redshift range 0.002 < z < 0.069, over a total path length cΔz = l16,000 km s~-1 . In this second paper, we evaluate the physical properties of these Lyα absorbers and compare them to their high-z counterparts. The SL 2 4 o distribution of Doppler parameters is similar to that at high redshift, with (b) = 38.0 ± l5.7 km s~-1. The true Doppler parameter may be somewhat lower, owing to component blends and nonthermal velocities. The distribution of equivalent Widths exhibits a significant break at W ≤ 133 mA. with an increasing number of weak absorbe,s (l0 mA < W < l00 mA). Adopting a curve of growth with b = 25 ± 5 km s~-1 and applying a sensitivity correction as a function of equivalent width and wavelength, we derive the distribution in column density, N~-1.72±0.06_H1, for l2.5 ≤ log [N_HI] ≤S 140.