What sparks the radio-loud phase of nearby quasars?

Abstract

To better constrain the hypotheses proposed to explain why only a few quasars\nare radio loud (RL), we compare the characteristics of 1958 nearby $(z\\le 0.3)$\nSDSS quasars, covered by the FIRST and NVSS radio surveys. Only 22\\% are RL\nwith $\\log(L_{1.4{\\rm GHz}}) \\ge 22.5$ W Hz$^{-1}$, the majority being compact\n(C), weak radio sources (WRS), with $\\log(L_{1.4{\\rm GHz}}) < 24.5$ W\nHz$^{-1}$. 15\\% of the RL quasars have extended radio morphologies: 3\\% have a\ncore and a jet (J), 2\\% have a core with one lobe (L), and 10\\% have a core\nwith two lobes (T), the majority being powerful radio sources (PRS), with\n$\\log(L_{1.4{\\rm GHz}}) \\ge 24.5$ W Hz$^{-1}$. In general, RL quasars have\nhigher bolometric luminosities and ionisation powers than radio quiet (RQ)\nquasars. The WRS have comparable black hole (BH) masses as the RQ quasars, but\nhigher accretion rates or radiative efficiencies. The PRS have higher BH masses\nthan the WRS, but comparable accretion rates or radiative efficiencies. The WRS\nalso have higher $FWHM_{\\rm [OIII]}$ than the PRS, consistent with a coupling\nof the spectral characteristics of the quasars with their radio morphologies.\nInspecting the SDSS images and applying a neighbour search algorithm reveal no\ndifference between the RQ and RL quasars of their host galaxies, environments,\nand interaction. Our results prompt the conjecture that the phenomenon that\nsparks the radio-loud phase in quasars is transient, intrinsic to the AGN, and\nstochastic, due to the chaotic nature of the accretion process of matter onto\nthe BHs.\n