Left panel: the field of view of GRB 050730 (z = 3.969) observed in F775W with HST/ACS. Middle panel: zoom-in on the inner 288. The different slit orientations from Table 1 are overplotted. Right panel: zoom-in on the inner 6′′; the panel was smoothed by a boxcar filter (width: ). The afterglow position is marked by an “ × ” in all panels. The 100-kpc radius (shown in the middle panel) represents the assumed maximum impact parameter of the absorber at z = 3.56. Objects are labelled if they lie within the circle and if they are covered by any of the slits. Their magnitudes are summarised in Table 4.