8. AN OLD VISION OF A NEW CLUSTER: SUMMARY AND CONCLUSIONS
At the end of this long yet not exhaustive historical review, one is left with
the feeling that everything was already known since long ago. It is sufficient
to have a quick look to the important steps in our scientific understanding
of the Coma cluster, before 1980:
- 1901: Wolf gives a map of Coma in which the SW group is already clearly
visible;
- 1937: Zwicky discovers the "missing-mass" problem;
- 1954: Shane & Wirtanen's galaxy counts also show very clearly the SW
subcluster;
- 1957: Zwicky finds that bright and faint galaxies have different
radial distributions;
- 1958: Zwicky shows that the "missing-mass" problem is a "dark-matter"
problem, because clusters are stable and non-expanding;
- 1959: Abell finds the secondary peak in the otherwise monotonically
increasing luminosity function of Coma galaxies;
- 1959: Large et al. detect Coma C, the radio-halo, at 408 MHz;
- 1960: Mayall shows that the velocity dispersion decreases with
increasing clustercentric distance;
- 1961: van den Bergh makes the first objective detection of subclustering
in Coma;
- 1966: Reaves suggests that the lack of dwarf galaxies in the Coma core
is due to tidal disruption;
- 1971: Meekins et al. discover the X-ray emitting IC gas in Coma;
- 1973: Bahcall suggests the existence of subclustering around
each of the two central dominant galaxies;
- 1973: des Forêts & Schneider show that galaxies of different types
have different velocity distributions;
- 1975: Lecar shows that the lack of significant luminosity
segregation imply that cluster galaxies have lost their halos;
- 1978: Sullivan & Johnson find three HI-deficient spirals in Coma;
- 1979: Johnson et al.'s X-ray map of Coma hints at the presence of a SW
extension.
At the time they were produced, many of these early results needed firm
confirmation, that eventually came from more (and more accurate) data;
on the other hand, our theoretical understanding of these observational
evidences is still far from complete. However, it seems to me that the
picture of a dynamically young Coma cluster was already contained in these
early results. So, maybe a more appropriate choice for this conference title
could have been: "An Old Vision of a New Cluster".
Acknowledments
This paper is dedicated to my wife Patrizia, for sharing my busy life of
wandering astronomer.
No historical review is unbiased. I apologize for the excessive emphasis I may
have put on my personal results, and for all other people's results that I have
misquoted or forgotten to mention.
I wish to thank Fabienne Casoli, Florence Durret, Daniel Gerbal, Alain Mazure,
for the perfect organization of this conference. I thank Michael West for
pointing out to me Herschel's work on the Coma cluster.
I acknowledge the hospitality of the Trieste Astronomical Observatory,
where a significant part of my bibliographic research was done.