Nature 379, 613 - 616 (15 February 1996); doi:10.1038/379613a0

Galaxy harassment and the evolution of clusters of galaxies

Ben Moore^*, Neal Katz^*, George Lake^*, Alan Dressler^† & Augustus Oemler^‡

^* Department of Astronomy, University of Washington, Seattle, Washington 98195-1580, USA
^† Observatories of the Carnegie Institution of Washington, Pasadena, California 91101-1292, USA
^‡ Yale University Astronomy Department, New Haven, Connecticut 06511, USA

NEARBY clusters of galaxies are filled with red elliptical 'E' and lenticular 'SO' galaxies¹, while younger clusters (at redshifts of > 0.4) contain substantial populations of blue spiral galaxies with morphological peculiarities^2–7 (see Fig. 1). Thus, within the last 4–5 billion years, galaxies in clusters underwent strong evolution that completely changed their character. By contrast, galaxies that are not associated with clusters show far less morphological evolution⁸. Here we propose that multiple highspeed encounters between galaxies—'galaxy harassment'— drives the morphological evolution in clusters. Our simulations show that these encounters are very different from mergers; they transform small disk galaxies into dwarf elliptical or dwarf spheroidal galaxies. Harassment will leave detectable debris arcs and could provide fuel for quasars in sub-luminous host galaxies.

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