A deep survey of fields around z > 4 quasars

Abstract

A deep three-color (B, I, and K) imaging survey was undertaken to search for z > 4 galaxies in the area surrounding known z > 4 QSOs. We have detected a slight excess of bright (K ~19) red (I - K ~3.5) galaxies in the QSO fields. If they are indeed at z > 4, they must be extremely bright (~100L*). Their red colors suggest that these objects are heavily reddened or already matured at z ~ 4, giving a possible explanation for the non-detections of previous Lyα PG surveys. On the other hand, their color and magnitude also match what is expected for an L* elliptical at z ~1. If this is the case, this result supports the premise that there are well-formed ellipticals at z ~ 1, and they are abundant enough to be the progenitors of present L* field galaxies. This strengthens the recently emerging picture that bright normal galaxies are quite quiescent up to z ~ 1 or higher, implying very high formation redshifts for these galaxies. Our scheduled ISO observation of one of the QSO fields should help determine which interpretation applies to these galaxies. Finally, no new population of possible z > 4 galaxies is appearing near the detection limit of K = 21 in these QSO fields.