Dissecting the properties of optically-thick hydrogen at the peak of cosmic star formation history

Understand

We present results of a blind survey of Lyman limit systems (LLSs) detected in absorption against 105 quasars at z~3 using the blue sensitive MagE spectrograph at the Magellan Clay telescope.

• By searching for Lyman limit absorption in the wavelength range ~3000-4000A, we measure the number of LLSs per unit redshift l(z)=1.21+/-0.28 at z~2.8.
• Using a stacking analysis, we further estimate the mean free path of ionizing photons in the z~3 Universe lambda^912 = 100+/-29 Mpc/h_70.4.
• Combined with our LLS survey, we conclude that systems with log N_HI >= 17.5 cm^-2 contribute only ~40% to the observed mean free path at these redshifts.