Speaker
Description
Radio emission from radio loud galaxies is dominated by synchrotron radiation from their powerful radio jets. Their radio quiet counterparts lack these powerful jets hence their source of radio emission is still unclear hence several options have been proposed including; AGN winds, corona, jets and star formation. In this work, we use NGC 1068 as a representative candidate of a radio quiet galaxy, to investigate the source of its nuclear radio emission. NGC 1068 is a prototypical radio quiet Seyfert 2 galaxy. We present a detailed study of the radio to sub-millimeter emission from the nucleus of NGC 1068. For this, we analyse observations between 5-700 GHz, matching them in resolution (0.06$''$) and $uv$-coverage (15$-$3300~k$\lambda$), in order to derive a consistent spectral energy distribution (SED), fitting synchrotron, free-free, dust and for the first time, a coronal component in the sub-mm. We confirm that the (sub)mm excess between $\sim 300$--700 GHz is consistent with synchrotron emission from a compact and optically thick corona with a radius $R_\mathrm{c}\approx(89\pm7)\,R_\mathrm{g}$, a fraction of $\sim$9% of the energy density in the form of non-thermal electrons, and a magnetic field strength $B\approx 148$ G.The detection of a corona provides strong evidence of the radio-mm/sub-mm-X-ray correlation proposed in the recent studies of radio-quiet AGN. The luminosity of the corona is roughly consistent with, though higher than the expected, from mm-X-ray correlations derived in recent studies of radio quiet AGN. This difference is likely due to the corona SED peaking at higher frequencies ($\approx$550 GHz). Below $\sim$200 GHz, the SED is dominated by free--free emission. High angular resolution observations at frequencies below 5~GHz are needed to constrain a putative optically-thin synchrotron component and the amount of free-free absorption.
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