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Merger Signatures in Radio Loud and Radio Quiet Quasars

Garofalo D., Webster B., Bishop K.

Acta Astronomica

2020

Vol. 70, No. 1

75--85

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.

3D joint inversion of Gradient and Mise-à-la-Masse borehole IP/Resistivity data and its application to magmatic sulfide mineral deposit exploration

Wondimu H. D., Mammo T., Webster B.

Acta Geophysica

2018

Vol. 66, no. 5

1031--1045

Gradient and Mise-à-la-Masse IP/Resistivity surveys were conducted on a group of 19 boreholes in Eagle’s Nest, Eagle One magmatic sulfide deposit in northern Ontario, Canada. The surveys were conducted as a follow-up to the many drilled boreholes, some of which missed the target. The surveys were intended to map the distribution of the ore mineralization, outline the deposit hosted by mafic and ultramafic rocks and then guide the drilling of new boreholes. Joint Gradient and Mise-à-la-Masse data inversion produced 3D chargeability and conductivity models. The inverted 3D models in turn help delineate the outline of the mineralized zone, and determine the shape, size, strength and economic viability of the deposit. The Gradient array determined the direction of the mineralization with respect to the boreholes, and the Mise-à-la-Masse array examined the highly conductive subsurface bodies and their surroundings. The mapped ore zone shows close similarity to the 0.5 Cu% and 1.05 Ni% iso-surfaces that are produced from core assay result confirming the reliability of the results obtained in this study.