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For refcode 1990ApJS...74..675B:
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1990ApJS...74..675B ASSOCIATIONS BETWEEN QUASI-STELLAR OBJECTS AND GALAXIES G. BURBIDGE AND A. HEWITT Center for Astrophysics and Space Sciences, University of California, San Diego AND J. V. NARLIKAR AND P. DAS GUPTA Tata Institute of Fundamental Research, Bombay, India, and Inter-University Center for Astronomy and Astrophysics, Poona University Campus, Pune, India Received 1989 July 13; accepted 1990 March 30 ABSTRACT We present a table listing all close pairs of QSOs and galaxies that we have been able to find in a computer-aided search of the extensive QSO catalog of Hewitt and Burbidge and the bright galaxy catalog of Sulentic and Tifft, together with an extensive search of the literature. The table contains 577 QSOs and more than 500 galaxies, and includes 28 low-redshift QSOs associated with 42 galaxies with the same redshifts as the QSOs. For the remainder, z_Q_ >> Z_G_, since even when no galaxy redshift has been measured, we know that for m_G_ < 21, a normal galaxy will have z_G_ <= 0.2. The majority of the angular separations of the pairs are less than 10', corresponding, for example, to a maximum projected linear separation for z_G_ = 0.01 of about 180 kpc (H_0_ = 50 km S^-1^ Mpc^-1^). In addition to the pairs so far described, we have also looked for pairings between 3CR radio galaxies and QSOs. For most of the pair involving a powerful radio galaxy listed in the table, the separations are in excess of 1 Mpc and must be accidental. In only seven cases are the pairs close enough that physical associations may be suspected, so that only those cases are used in our general analysis. We show in two figures that 300 and 278 pairs, respectively , in which z_Q_ >> z_G_, there is a large excess of pairs with separations of 2' or less, or about 60 kpc, over the numbers expected if the configurations were accidental, thus suggesting that the pairs are physically associated. We analyze the plot z_G_ against the angular separation {theta} for 392 pairs. In 1972, when only five close galaxy-QSO pairs had been identified from a complete sample of QSOs and bright galaxies, it was shown that {theta} was proportional to z^-1^, thus adding further to the evidence for physical association. This relation was further investigated in 1980, and now, with more than 390 pairs, the relation is till present. We discuss selection effects which bear on it and show that they are not important. Our conclusion is that there is strong evidence that normal galaxies and QSOs tend to be clustered whether or not their redshifts are the same. This result supports the earlier work showing that many bright galaxies and QSOs with large redshift are physically associated, that small redshift QSOs and galaxies with the same redshift are clustered, and also the more recent work of Webster and her colleagues showing that faint galaxies tend to be clustered around high-redshift QSOs at very small separations (<= 6"). We believe that a general rule can be stated as follows: QSOs tend to lie in the vicinity of normal galaxies much more often than is expected by chance, whether or not the galaxies and the QSOs have the same redshifts. This rule can be extrapolated to apply to situations in which a single high-redshift galaxy is seen apparently in interaction with a small group (triplet, quartet, quintet, etc.) of galaxies all of about the same (lower) redshift. In the final sections we emphasize that this rule cannot be explained in terms of gravitational microlensing because, on the one hand, there are not enough faint QSOs to explain the effect seen at comparatively large angular separations involving bright galaxies, and, on the other, there is not enough mass (and hence mass points) to explain the effect where faint galaxies are seen very close to high-redshift QSOs. It is concluded that some part of the redshift of all classes of active nuclei is not associated with the expansion of the universe. Several possible explanations are briefly described. Subject headings: galaxies: clustering - galaxies: redshifts - gravitational lenses - quasars - radio sources: galaxies
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