The Space Distribution of the Lyman Alpha Clouds in the Line of Sight to the Z=3.66 QSO 0055-269

The spectrum of the quasar Q0055-269 ($z=3.66$) has been observed at the resolution of 14 km s${}^{-1}$ in the wavelength interval 4750–6300 \AA. We give a list of Lyman$-\alpha$ lines and metal-line systems for which column densities and Doppler widths have been derived by a fitting procedure. The statistical distribution of the Doppler parameter for the Lyman$-\alpha$ lines is peaked at $b\simeq 23$ km s${}^{-1}$, with 13% of lines with $15\leq b\leq 20$kms$^{-1}$\mathrm{.}ThecolumndensitydistributionoftheLyman$-\alpha$ lines is described by a power-law with a break or cutoff at $\log N_{HI}\simeq 14.5$. A featureless power-law distribution is rejected with a probability of $99.94$%. Significant clustering, with $\xi \simeq 1$ at $\mathrm{\Delta }v=100$ km s${}^{-1}$, is detected only for lines with $\log N_{HI}\text{magcir}13.8$. In addition, two voids of size $\sim 2000$ km s${}^{-1}$ are found in the spectrum with a random probability of $2\times {10}^{-4}$. {}From the proximity effect for lines in the interval $\log N_{HI}=13.3-14.2$ it is possible to infer an UV ionizing background $J=5\times {10}^{-22}$ ergs s${}^{-1}$ cm${}^{-2}$ Hz${}^{-1}$ sr${}^{-1}$, within a factor of two from the integrated quasar contribution.