SURFACE PHOTOMETRY OF EARLY-TYPE GALAXIES IN THE HUBBLE DEEP FIELD

The detailed surface photometry of a sample of early-type galaxies in the Hubble Deep Field is presented as part of a long-term project aime d to settle strong observational constraints to the theories modelling the evolution of elliptical galaxies from the early stages. The sampl e has been extracted, in the V-606 band, from the database provided by the ESO-STECF-HDF Group (Couch 1996). The selection criteria involve the total magnitude, the number of pixels detected above the backgroun d level and an automatic star/galaxy classifier. Moreover, form visual inspection of the frames, we excluded the galaxies showing unambiguou s late-type morphology. The analysis of the luminosity and geometrical profiles, carried out on the 162 candidates obeying our selection cri teria, resulted in a list of 99 ''bona fide'' early-type galaxies, for which accurate total magnitudes and effective radii were computed on the basis of the equivalent luminosity profiles. The comparison with t he magnitudes given by Williams et al. (1996) indicates that the autom ated photometry tends to underestimate the total luminosity of the ell ipticals.The luminosity profiles of most of galaxies in our sample fol low fairly well the de Vaucouleurs law (''Normal'' profiles). However, a relevant fraction of galaxies, even following the r(1/4) law in the main body light distribution, exhibit in the inner region a flattenin g of the luminosity profile not attributable to the PSF (''Flat'' prof iles) or, in some cases, a complex (multi-nucleus) structure (''Merger '' profiles). A statistically significant correlation is found between the shapes of the luminosity profiles and the ellipticity distributio n. In particular, the average ellipticity of galaxies belonging to the ''Flat'' and ''Merger'' classes is significantly higher than that of the ''Normal'' galaxies. Finally, even taken into account the relevant uncertainty of the outer position angle profiles, the amount of isoph otal twisting of HDF ellipticals turns out to be significantly larger with respect to that of the local samples.