AAS 197, January 2001
Session 108. Radio Observations of Active Galaxies
Display, Thursday, January 11, 2001, 9:30-4:00pm, Exhibit Hall

[Previous] | [Session 108] | [Next]

[108.04] Radio Emission from Quasar-2 Candidates

J.S. Ulvestad (NRAO), S.G. Djorgovski, R.J. Brunner, A. Mahabal (Caltech)

A ``missing link'' in unified schemes for active galaxies has been the lack of a populous group of radio-quiet type 2 quasars (hereafter ``Q2s''), the more distant and powerful analogs of the narrow-lined Seyfert 2 galaxies. Recently, a population of Q2 candidates has been revealed in the redshift range 0.31 \leq z \leq 0.37, by means of extremely strong [O~III] emission found during spectroscopic follow-up observations of the Digital POSS-II (Djorgovski et al.~1999, BAAS, 31, 1467).

Nineteen Q2 candidates were observed in August 2000 using the Very Large Array in its most compact configuration, at a frequency of 8.4~GHz. Fourteen detections were achieved within 3'' of the optical positions of the candidates, with flux densities ranging from 70~\muJy to 1500~\muJy. The corresponding radio powers lie between 1022 and 1024~W~Hz-1, implying that the Q2 candidates are radio-quiet, and overlap the upper end of the radio luminosity function for Seyfert 2 galaxies. The ratio of radio power to [O~III] luminosity is consistent with the well-known relationship between those quantities for Seyfert~2 galaxies. Finally, the radio powers are consistent with those of radio-quiet quasars within the same redshift range, after allowance is made for possible differences in the radio/[O~III] ratios for type 1 and type 2 objects. Therefore, the radio imaging confirms a substantial population of type 2 quasars with optically weak continua. This is consistent with the hypothesis that these objects contain a nuclear torus that is closer to edge-on than to face-on, blocking the continuum radiation that excites the powerful [O~III] emission.

The National Radio Astronomy Observatory is a facility of the National Science Foundation operated under cooperative agreement by Associated Universities, Inc.

[Previous] | [Session 108] | [Next]