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| doi: 10.32023/0001-5237/70.1.5 | Vol. 70 (2020), No. 1 | pp. 75-85 |
Merger Signatures in Radio Loud and Radio Quiet Quasars
D. Garofalo, B. Webster and K. Bishop
Department of Physics, Kennesaw State University, Marietta, GA 30060, USA
Received: January 24, 2020
ABSTRACT
While the origin of the radio loud/radio quiet dichotomy is still debated, the consensus is that radio loud and radio quiet quasars are both triggered by mergers, yet merger signatures are not evenly distributed among the two groups. Whereas they are detected in radio loud quasars at a rate of 80-100%, the rate is considerably smaller in radio quiet quasars at 20-30%. Because the radio loud/radio quiet dichotomy is a counterrotation/co-rotation accretion dichotomy around spinning black holes in our paradigm, and counterrotation spins black holes down rapidly, radio loud quasars live comparably shorter lifetimes. As a result, they are more likely to be observed when less time elapses from the merger that triggered them. In order to check our model, we work backwards from the observed merger rates to obtain accretion rates for both the jetted and non-jetted quasars in our model. The goal is to check the model prescription that both families of active galaxies accrete at a rate that is compatible with cold, radiatively efficient, thin disks.
We find that if average accretion rates in radio loud quasars span the
range 2-80% of the Eddington accretion rate, we obtain a match with
the observed 80-100% rate of merger signatures. Because radio quiet
quasars emerge in different ways in the model with phases whose
lifetimes vary by much more, from a few million to a billion years,
the rates of merger signatures are more difficult to obtain.
Nonetheless, we show that for the radio quiet quasars with longest
lifetimes that should dominate the merger signature rates, average
accretion rates in the range 5-7.5% of the Eddington limit make
theory compatible with observations. Interestingly, these numbers are
compatible with the assumption in the model that the relevant radio
quiet quasars in the analysis live longer and therefore experience a
decline in accretion rate over time.
Key words:
quasars: general - quasars:
supermassive black holes - Galaxies: active
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