Constraints from the Hubble Deep Field on High‐Redshift Quasar Models

High resolution, deep imaging surveys are instrumental in setting constraintson semi-analytical structure formation models in Cold Dark Matter (CDM)cosmologies. We show here that the lack of unresolved B-band ``dropouts'' withV > 25 mag in the Hubble Deep Field (HDF) appears to be inconsistent with theexpected number of quasars if massive black holes form with a constantuniversal efficiency in all CDM halos. To reconcile the models with the data, amechanism is needed that suppresses the formation of quasars in halos withcircular velocities v(circ) < 50-75 km/s. This feedback naturally arises due tothe photoionization heating of the gas by the UV background. We considerseveral alternative effects that would help reduce the quasar number counts,and find that these can not alone account for the observed lack of detections.If reddening by dust can be neglected at early epochs, consistency with theoptical data also requires that the luminous extent of dwarf galaxies at highredshifts be larger than a few percent of the virial radii of their dark matterhalos, in order not to overpredict the number of point-like B-band dropouts.Future deep observations in the J and H bands with NICMOS might reveal severalz > 5 objects per field or provide even stronger constraints on the models thanexisting B, V, and I data.Comment: 21 pages, latex, 6 figures included, submitted to Ap