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Coma is one of the most studied clusters of galaxies of the sky, along with Virgo and Perseus (1). While being the most distant of the three, with a mean redshift z appeq 0.023, Coma has also been the most appealing to observers because of its location near the galactic pole (bII = 88°) and because of its richness (2).

Another characteristic that differentiates Coma from Virgo and Perseus is its regular and (roughly) spherical shape. In Shane & Wirtanen [122]'s words:

There appear to be two extreme structural types among the populous clusters, exemplified by the Virgo and the Coma clusters. The Virgo type is characterized by the absence of a strong central condensation and by lack of symmetry [...] The Coma-type cluster is characterized by a strong central condensation and a tendency towards spherical symmetry.

What could be more charming than spherical symmetry (even if only approximate, see e.g. Schipper & King [119]) for a theoretician? It is indeed not surprising that Coma has been chosen as the prototype cluster by theoreticians, since the early papers of Zwicky [163], [164] and others (e.g. Carpenter [25], Holmberg [70], Tuberg [141]), and until the recent estimates of the density of matter in the Universe (e.g. the "baryon catastrophe" of Briel et al. [19]) and recent scenarios for the structure formation (e.g. the "filament" scenario of West et al. [154]).

Nevertheless, Coma's richness and regularity are not typical of all clusters. As Kent & Gunn [78] pointed out:

Coma is quite atypical among clusters in its richness, compactness, and degree of symmetry.

On the other hand, the title of this conference indicates that we now have "a new vision" of Coma, that emerged through the (once controversial) works of many people (e.g. Fitchett & Webster [47], Mellier et al. [93]). As Biviano et al. [16] wrote:

Coma can now be considered as the prototype of rich clusters endowed with subclusters, and thus not fully relaxed

Figure 1

Figure 1. The number of papers published on the Coma cluster through the years (dashed line), and the ratio between the number of papers published on Coma and the number of papers published on galaxy clusters in general (solid line).

The interest of the astronomical community in Coma can be traced by counting the number of publications dealing with this cluster, through the years. While the total number of publications on Coma has continuously increased with time (Fig. 1), the increase rate diminished in the 70's, when Coma became one of many well-studied clusters. This can be also seen by plotting the same number divided by the number of publications on galaxy clusters in general (Fig. 1): there is a continuously decreasing trend from the 70's on. No doubt the proceedings of this conference will mark a change in this trend!

In the next sections I will describe how our vision of Coma has evolved through the years (3). For topics not covered in this review, I refer the reader to the contributions of Feretti, Gavazzi, Jones, and West in these same proceedings.

1 Of the three clusters, Perseus was never dedicated a whole conference, while it was the case for Virgo [148] and Coma (these proceedings). Back.

2 Of the nearby clusters (distance class leq 1) only five are as rich or richer than Coma (according to Abell et al. [6]). Back.

3 I have stopped my historical review with the year 1995. More recent works are cited only occasionally (with a possible bias towards my owns!). Back.

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