Inter-comparison of Radio-Loudness Criteria for Type 1 AGNs in the XMM-COSMOS Survey

Abstract

Limited studies have been performed on the radio-loud fraction in X-ray selected type 1 AGN samples. The consistency between various radio-loudness definitions also needs to be checked. We measure the radio-loudness of the 407 type 1 AGNs in the XMM-COSMOS quasar sample using nine criteria from the literature (six defined in the rest-frame and three defined in the observed frame): R_L = log(L_(5GHz)/L_B), q_(24) = log(L_(24μm)/L_(1.4GHz)), R_(uv) = log(L_(5GHz)/L _(2500°A)), R_i = log(L_(1.4GHz)/L_i), R_X = log(νL_ν (5GHz)/L_X), P_(5GHz) = log(P_(5GHz)(W/Hz/Sr)), R_(L,obs) = log(f_(1.4GHz)/f_B) (observed frame), R_(i,obs) = log(f_(1.4GHz)/f_i) (observed frame), and q_(24,obs) = log(f_(24μm)/f_(1.4GHz)) (observed frame). Using any single criterion defined in the rest-frame, we find a low radio-loud fraction of ≲5% in the XMM-COSMOS type 1 AGN sample, except for R_(uv). Requiring that any two criteria agree reduces the radio-loud fraction to ≲2% for about 3/4 of the cases. The low radio-loud fraction cannot be simply explained by the contribution of the host galaxy luminos ity and reddening. The P_(5GHz) = log(P_(5GHz)(W/Hz/Sr)) gives the smallest radio-loud fraction. Two of the three radio-loud fractions from the criteria defined in the observed frame without k-correction (R_(L,obs) and R_(i,obs)) are much larger than the radio-loud fractions from other criteria.

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