86 GHz VLBI Survey of Ultra Compact Radio Emission in Active Galactic Nuclei

TLDR: In this article, the authors used gaussian model fitting to estimate the brightness temperature of the VLBI bright core (base) of the jet and inner jet components of AGN, taking into account the resolution limits of the data at 3mm.

Abstract: Very Long Baseline Interferometry (VLBI) Observations at 86 GHz reach a resolution of about 50 microarcseconds and sample the scales as small as 1010 Schwartzchild radii of the central black hole in Active Galactic Nuclei (AGN), and uncover the jet regions where accelaration and collimation of the relativistic flow takes place. Synchrotron radiation becomes optically thin at millimetre wavelengths ; making it possible to look deeper into the core and inner jets of AGN which is invisible at cm and longer wavelengths due to self absorption or free-free absorption by the torus. We present here results from a large global VLBI survey of 168 ultracompact radio sources at 86 GHz conducted in 2010 2011. All the sources were detected and imaged ; increasing by a factor of ~ 2 the total number of AGN imaged with VLBI at 86 GHz. We use gaussian modelfitting to represent the structure of the observed sources. The modelfitting yields estimates of the brightness temperature (Tb) of the VLBI bright core (base) of the jet and inner jet components of AGN, taking into account the resolution limits of the data at 3mm. We also compare the brightness temperature of the VLBI cores from this 86 GHz survey with similar estimates from the MOJAVE VLBI surveys at 15 GHz. We also compare the brightness temperatures obtained from the model fits with estimates of the brightness temperature limits made directly from the visibility data. For objects with sufficient structural detail detected, we investigate the effect of adiabatic energy losses on the evolution of brightness temperature along the jet.