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Paper: Quasar pairs at large redshifts
Volume: 21, The Space Distribution of Quasars
Page: 349
Authors: Djorgovski, S.
Abstract: A sample of apparently close physical pairs of quasars at large redshifts has been compiled. There are at least a half-dozen such systems now known. They seem to divide into two groups with about equal frequencies, approximately 10 exp -3 pairs per cataloged quasar: a set of wide, Mpc-scale pairs (arcmin separations), and a set of close pairs, with projected separations of a few arcsec, or not greater than 100 kpc. A simple hierarchical clustering model matches well the observed frequency of the wide pairs, but the close pairs are about two orders of magnitude overabundant relative to the predictions of this model. This is interpreted as a signature of galaxy interactions, which trigger the nuclear activity in both members of close quasar pairs. These systems may represent birth events of quasars at the epoch where the comoving density of quasars was near its maximum.
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