The low-redshift Lyα forest towards 3C 273

We present an analysis of the Ly alpha forest towards 3C 273 from the Space Telescope Imaging Spectrograph at similar to 7 km s(-1) resolution, along with reprocessed data from the Far Ultraviolet Spectroscopic Explorer. The high ultraviolet flux of 3C 273 allows us to probe the weak, low-z absorbers. The main sample consists of 21 HI absorbers that we could discriminate to a sensitivity of log N(HI) approximate to 12.5. The redshift density for absorbers with 13.1 < log N (HI) < 14.0 is similar to 1.5 sigma below the mean for other lines of sight; for log N(HI) >= 12.5, it is consistent with numerical model predictions. The Doppler parameter distribution is consistent with other low-z samples. We find no evidence for a break in the column density power-law distribution to log N(HI) = 12.3. A broad Ly alpha absorber is within Delta v <= 50 km s(-1) and 1.3 local-frame Mpc of two similar to 0.5L* galaxies, with an O VI absorber similar to 700 km s(-1) away, similarly close to three galaxies and indicating overdense environments. We detect clustering on the Delta v < 1000 km s(-1) scale at 3.4 sigma significance for log N(HI) >= 12.6, consistent with the level predicted from hydrodynamical simulations, and indication for a Ly alpha forest void at 0.09 < z < 0.12. We find at least two components for the z = 0.0053 Virgo absorber, but the total N(HI) column is not significantly changed.