Hubble Space Telescope observations of the gravitationally lensed Cloverleaf broad absorption line QSO H1413+1143:: Spectroscopy of the Lyα forest and metal-line systems

The intervening Ly alpha forest and metal-line absorbers toward the "Cloverleaf" gravitational lens H1413+1143 (z(em) = 2.54, m(v) approximate to 17) are examined along the four individual sight lines using HST-FOS spectra. The observations probe the Ly alpha forest systems on size scales of up to 4 h(-1) kpc(H-o = 100 h km s(-1) Mpc(-1), q(o) = 0.5) and metal-line systems on scales up to 6 h(-1) kpc. The equivalent widths of Ly alpha forest lines in general are well correlated along the four different lines of sight and are consistent with the sight lines piercing the same absorbers. The heavy-element systems clearly show evidence for differences. One striking difference is seen in a system at z(abs) = 2.0969 in which the Ly alpha line possesses a column density approaching log N(H I) = 19.7 in component B but not exceeding log N(H I) = 18.4 in any of the other three components. Simulations show that a circular absorber responsible for such a scenario has a radius of less than or equal to 10 h(-1) kpc with a 90% confidence level, assuming a lens redshift of z(lens) = 1.55. The z(abs) = 1.6595 system contains a probable damped Ly alpha line and shows evidence for rotation. A system at z(abs) = 1.4377 exhibits very significant Fe II absorption in only two of the components at the level of sensitivity of the observations. Examination of how the absorption-line equivalent widths are correlated between the component spectra can provide information about whether all four lines of sight to the QSO are passing through the same absorbers, placing limits on absorber sizes and shapes. The four sight lines toward H1413+1143 provide a unique geometry for this type of study.