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We present spectra of QSOs 1343+266A, B, covering Ly $\beta$ to C~IV emission at 2\AA~resolution, and find further evidence that this system is not gravitationally lensed. We see, however, a large number of Ly $\alpha$ and some C~IV absorption features common to both spectra. The frequency of C~IV lines in common indicates that these absorbers have a radius close to the sightline separation, $39~h^{-1}$kpc (where $h \equiv (H_o / 100$ km s$^{-1}$ Mpc$^{-1}$, $q_o=0.5$), implying a spatial number density of these absorbers the same as current day $L>0.3L_*$ galaxies. Furthermore, the velocity mismatch for C~IV systems indicates absorber masses in the range $10^{11}~M_{\odot} < M < 10^{12}~M_{\odot}$. These results confirm that typical galaxies cause QSO C~IV-line absorption.
This system is well-suited for probing the Ly$\alpha$ forest, since the two component spectra show several Ly$\alpha$ lines in common and several others not. Using Bayesian statistics, under the idealization of uniform-radius spherical absorbers, we find that the Ly$\alpha$ cloud radius at $z \approx 1.8$ lies in the range $40h^{-1}$kpc$< R < 280 h^{-1}$kpc with $98\%$ confidence in a $(\Omega_o, \Lambda_o) = (1, 0)$ model universe. The median value of $R$ is $90h^{-1}$kpc. These numbers scale up by a factor 1.44 for $(\Omega_o, \Lambda_o) =(0.1, 0)$; and by a factor 1.85 for (0.1, 0.9). Pressure-confined and freely-expanding Ly$\alpha$ cloud models in which the absorbers formed in a significantly more compressed state at $z \gg 2$ are contradicted by these new data, as are models involving stably-confined gas concentrations in photoionization equilibrium within minihalos of cold dark matter. The comoving density of Ly$\alpha$ forest objects at $z\sim 2$ is $\sim 0.3 \, h \, (R/100$ kpc$)^{-2}$ Mpc$^{-3}$ in a (1,0) model universe. This suggests a possible identification of Ly$\alpha$ clouds with the unvirialized, collapsing progenitors of the faint, blue galaxies at $z\sim 1$.
