The radio properties of the broad-absorption-line QSOs

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Abstract

A VLA radio detection survey has been conducted for a large sample of broad-absorption-line (BAL) QSOs. Together with results from a similar, previous survey and a few observations from two other surveys, 68 BALQSOs have now been well observed with no strong radio sources detected. The absence of luminous radio sources among 68 known BALQSOs reported here, together with a complementary spectroscopic study which finds no BALQSOs among a large sample of radio-loud quasars, establishes a strong anticorrelation between luminous radio sources and the BALQSO phenomenon. Specifically, using a larger control sample of high-z, high-luminosity, optically selected non-BALQSOs than was previously available, we estimate the probability that no luminous radio sources were found among the BALQSOs to be ~1% if the BALQSOs were drawn from the same parent population as the non-BALQSOs. Applying a quantitative statistical test calibrated by Monte Carlo realizations, the long-suggested bimodal division of all QSOs into radio- loud and radio-quiet objects is found to be present at greater than 98% confidence level In several samples. Further, these tests suggest that the dividing line between radio-louds and radio-quiets occurs at log R^*^~1.0 or at log L_rad_~26 W Hz^-1^ for z~2 QSOs. There is some evidence that the separation between radio-loud and radio-quiet objects is less distinct for the most luminous QSOs with log L_opt_ > 24.8 [i.e., M(B) < - 28]. The BALQSOs are exclusively members of the radio-quiet population and have radio properties that are indistinguishable from other radio-quiet QSOs. However, the statistical basis for this last assertion is limited at present due to the lack of sufficient radio detections among high-z, radio-quiet QSOs. The absence of strong radio emitters among BALQSOs cannot be due solely to free-free absorption of the core source by the BAL cloud. We suggest that QSOs produce either a highly collimated, powerful, relativistic jet that gives rise to luminous radio emission or to a subrelativistic, uncollimated wind that accelerates the BAL clouds, but not both.

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