4.2. The Hubble Deep Field

The Hubble Deep Field (HDF) has given us unprecedented new views of distant galaxies. In combination with spectroscopic observations with the Keck Telescopes, studies of galaxies are now well advanced at z > 3, redshifts that were unattainable previously. Consequently, we now have the opportunity to study directly the relationship of galaxies and quasars at and beyond the redshift of peak quasar activity.

Recently Conti et al. (1998) have carried out a detailed search for compact quasars and AGNs in the HDF to V₆₀₆ = 27 mag to study their presence and behavior at luminosities corresponding to AGNs in the nearby universe. Although the HDF contains more than 3000 galaxies, Conti et al. found an upper limit of 20 for the number of quasar candidates. Based on spectroscopic observations to date, the actual number may be much smaller, even close to 0. However, because of the great depth of the HDF exposures and the ~ 0.1 arcsec image quality, it is possible that any AGNs in the HDF are spatially resolved, and the next step is to develop sensitive techniques to detect AGN within faint, resolved galaxies in the HDF. A complication is that many of the distant galaxies being found by HST and Keck are undergoing intense star formation, which gives them colors similar to those of many quasars. Jarvis and MacAlpine (1998) report identification of 12 resolved objects harboring candidate AGN. The crucial next step will be to confirm the nature of the candidates with follow-up spectroscopy, a very difficult task because of their faintness.