Deep imaging of high redshift QSO fields below the Lyman limit. I - The field of Q0000-263 and galaxies at Z = 3.4

We present the results for the first field completed in a new survey involving very deep imaging of the fields of high redshift QSOs which exhibit optically thick Lyman limit absorption systems which completely remove the QSO from the observed broadband ultraviolet bandpass. In particular, we examine the broadband colors of galaxies near the QSO sightline with knowledge of the redshifts of heavy element absorption systems already discovered in the QSO spectrum. Fortuitously, this first field examined, that of Q0000-263 (Zₑm_ = 4. 106) happens to be the same as a recently identified galaxy claimed to have z= 3. 408; our new data appear to rule out this redshift, on the basis of the absence of the expected flux decrement across the putative rest frame Lyman limit of the galaxy. We suggest that the colors and magnitudes are more consistent with a moderately underluminous galaxy at z=0. 438. However, we have identified a galaxy which is 2. 3 mag fainter and is only 2. 8" from the QSO sightline, which is undetected in our UV bandpass, and could plausibly be associated with the object responsible for the z= 3. 390 damped Lyman aLPHA absorption system in the spectrum of Q0000-263. The object, which we call galaxy "A, " is not implausibly luminous (L~3L^*^) if the identification is correct. Moreover, the projected separation of the galaxy from the QSO is in the range 10-19H^-1^₁00_ kpc at z = 3. 390, so that it is reasonable to suggest that galaxy A is responsible for giving rise to the damped Lyman α absorption. There is another object in the field (~25" from the QSO) with very similar colors and R magnitude (RAB_= 25), suggesting the possibility that the galaxies may have similar redshifts. These two galaxies are the only ones (of 35 total) within 30" of the QSO line of sight which have the expected colors for star-forming galaxies at z = 3. 390. Our new method of obtaining deep continuum observations in the fields of well-studied (spectroscopically) high redshift QSOs may provide significant advantages over the largely unsuccessful attempts using narrow-band imaging in search of substantial Lyman α emission.