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Astron. Astrophys. 364, 26-42 (2000)

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8. Summary and conclusions

We have implemented a code to analyze the surface brightness distribution of faint galaxies, optimized to work on deep HST images, and we have tested its performances on a large set of simulated galaxies. We have then used this code to fit model brightness distributions to a sample of 41 EROs, imaged by HST in the optical or near-infrared wide-band filters, in order to identify a set of high-z elliptical candidates on a morphological basis. The main results of this work can be summarized as follows.

a) We have determined the fraction of irregular objects among the EROs of our sample, amounting to about 15%. These galaxies are the favourite candidates to be the hosts of dusty starbursts.

b) Considering the whole sample, the galaxies characterized by a brightness distribution typical of local ellipticals are at least 50%. This estimate is based on a simple distinction between irregular/exponentials and de Vaucouleurs profiles; a more accurate analysis, allowing for different values of the shape index n, yields a higher fraction of ellipticals (70-80%).

c) We find that a rather small fraction of EROs (15 [FORMULA] 30%) is made up of compact objects whose brightness distributions do not resemble the ones of local elliptical galaxies, but are better described by a pure exponential law.

d) Our data suggest that irregular EROs are found predominantly in the field, and that they are characterized - on average - by the reddest colors.

e) We have determined the rest-frame Kormendy relation for a subsample of 6 cluster ellipticals, at redshift [FORMULA]. The relation turns out to be brighter than the local one, at fixed size, by 1.4 mag in the B band.

In the near future, we plan to extend this work to larger, complete samples of high redshift galaxies, in particular devoting our efforts to obtain a reliable picture of the whole population of high-redshift ellipticals.

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© European Southern Observatory (ESO) 2000

Online publication: December 15, 2000