The Column Density Distribution and Continuum Opacity of the
  Intergalactic and Circumgalactic Medium at Redshift <z>=2.4
  We present new high-precision measurements of the opacity of the
intergalactic and circumgalactic medium (IGM, CGM) at <z>=2.4. Using Voigt
profile fits to the full Lyman alpha and Lyman beta forests in 15
high-resolution high-S/N spectra of hyperluminous QSOs, we make the first
statistically robust measurement of the frequency of absorbers with HI column
densities 14 < log(NHI) < 17.2. We also present the first measurements of the
frequency distribution of HI absorbers in the volume surrounding high-z
galaxies (the CGM, 300 pkpc), finding that the incidence of absorbers in the
CGM is much higher than in the IGM. In agreement with Rudie et al. (2012), we
find that there are fractionally more high-NHI absorbers than low-NHI absorbers
in the CGM compared to the IGM, leading to a shallower power law fit to the CGM
frequency distribution. We use these new measurements to calculate the total
opacity of the IGM and CGM to hydrogen-ionizing photons, finding significantly
higher opacity than most previous studies, especially from absorbers with
log(NHI) < 17.2. Reproducing the opacity measured in our data as well as the
incidence of absorbers with log(NHI) > 17.2 requires a broken power law
parameterization of the frequency distribution with a break near log(NHI) ~ 15.
We compute new estimates of the mean free path (mfp) to hydrogen-ionizing
photons at z=2.4, finding mfp = 147 +- 15 Mpc when considering only IGM
opacity. If instead, we consider photons emanating from a high-z star-forming
galaxy and account for the local excess opacity due to the surrounding CGM of
the galaxy itself, the mean free path is reduced to mfp = 121 +- 15 Mpc. These
mfp measurements are smaller than recent estimates and should inform future
studies of the metagalactic UV background and of ionizing sources at z~2-3.
