Global Millimeter VLBI Array Survey of Ultracompact Extragalactic Radio Sources at 86 GHz

Very Long Baseline Interferometry (VLBI) observations at 86 GHz ($\sim 3$ mm) reach a resolution of about 50 micro arcsec and sample the scales as small as $10^{3}-10^{4}$ Schwarzschild radii of the central black hole in Active Galactic Nuclei (AGN), and uncover the jet regions where acceleration and collimation of the relativistic flow takes place. We present results from a large global 86 GHz VLBI survey of 162 ultra compact radio sources conducted in 2010-2011 using the Global Millimeter VLBI Array (GMVA). This survey has contributed an increase of $\sim 2$ on the total number of AGN ever imaged with VLBI at 86 GHz. For the first time, 3 mm VLBI maps of 138 sources are made. The survey data attained a baseline sensitivity of 0.1 Jy and a typical image sensitivity of 5 mJy/beam. Gaussian model fitting was used to represent the structure of the observed sources and to estimate the flux densities and sizes of the core and jet components. The model fitting yields estimates of the brightness temperature (T b ) 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. The model fit based estimates of brightness temperatures were compared to the estimates of brightness temperature limits made directly from the visibility data, demonstrating a good agreement between the two methods.