DEEP PROBING OF THE COMA CLUSTER

As a continuation of our study of the faint galaxy luminosity function in the Coma cluster of galaxies, we report here on the first spectros copic observations of very faint galaxies (R less than or equal to 21. 5) in the direction of the core of this cluster. Out of these 34 galax ies, only one may have a redshift consistent with Coma, all others are background objects. The predicted number of Coma galaxies is 6.7 +/- 6.0, according to Bernstein et al. (1995, B95). If we add the 17 galax ies observed by Seeker (1997), we end up with 5 galaxies belonging to Coma, while the expected number is 16.0 +/- 11.0 according to B95. Not ice that these two independent surveys lead to the same results. Altho ugh the observations and predicted values agree within the error, such results raise into question the validity of statistical subtraction o f background objects commonly used to derive cluster luminosity functi ons (e.g. B95). More spectroscopic observations in this cluster and ot hers are therefore urgently needed. As a by-product, we report on the discovery of a physical structure at a redshift z similar or equal to 0.5.