We present images and spectroscopy of objects close to the sightline of Q2302+029 in order to search for galaxies responsible for the remarkable z\ > = \ > 0.7 high-ionization absorption line system found by .
This system shows ‘ normal ’ narrow O VI , N V , and C IV lines superimposed on broader ( 3,000 - 5,000 km s ^ { -1 } wide ) , unsaturated absorption troughs some 56,000 km s ^ { -1 } away from the QSO emission redshift ( z _ { em } \ > = \ > 1.052 ) .
Despite reaching sensitivities sufficient to detect 1 / 10 L ^ { * } galaxies in the optical and 1 / 20 L ^ { * } in the infra-red , we are unable to detect any obvious bright galaxies which might be responsible for the absorption beyond \approx 6 h ^ { -1 } kpc of the sightline .
This supports the hypotheses that the absorption is either intrinsic to the QSO , or arises in intracluster gas .
Adopting either explanation is problematic : in the first case , ‘ associated ’ absorption at such high ejection velocities is hard to understand , and challenges the conventional discrimination between intrinsic and intervening absorbers ; in the second case , the gas must reside in a \sim \ > 40 h ^ { -1 } Mpc long filament aligned along the line of sight in order to reproduce the broad absorption .
Since the absorption system is unusual , such a chance alignment might not be unreasonable .

Spectroscopy of objects beyond the immediate vicinity of the QSO sightline reveals a galaxy cluster at z\ > = \ > 0.59 , which coincides with strong Ly \alpha and more narrow high ionization lines in the quasar spectrum .
Here too , the lack of galaxies at distances comparable to those found for , e.g. , Ly \alpha -absorbing galaxies , suggests that the absorption may arise from intracluster gas unassociated with any individual galaxies .