Optically dim counterparts of hard X-ray selected AGNs

We present near-IR photometry and imaging observations of a small sample of sources identified in the BeppoSAX 5-10 keV survey (HELLAS) which resolves similar to 20-30% of the X-ray background at these energies. The near-IR d ata are combined with optical spectra and photometry. Only 40% of the sourc es in our sample have the blue, power law continuum typical of color-select ed QSOs. The remaining 60% are dominated by a galactic component which, on the basis of the continuum colors and shape, have ages ranging from 10(9) t o 10(10) years. The images show that the blue QSOs are pointlike at our ang ular resolution, while all the other sources are extended, consistent with their spectral appearance and low redshift. Since down to R = 20 only about two thirds of the HELLAS sources have a counterpart, the preliminary HELLA S census comprises in roughly equal parts: i) blue QSOs (mostly at high red shifts); ii) optically dim, galaxy-dominated active nuclei (mostly at modes t redshifts); and iii) empty fields (possibly highly absorbed QSOs at high redshifts).