Astronomy Colloquium (2016 Fall Semester)

* Date

Nov. 3

* Speaker

Jeffrey Hodgson (KASI)

* Title

VLBI – What can we do at the highest resolutions?

* Abstract

Very Long Baseline Interferomatry is a technique that has long been used to achieve extremely high angular resolution. With telescopes such as the Event Horizon Telescope (EHT), RadioAstron and the Global mm VLBI Array (GMVA), angular resolution of the 20-50 microarcseonds is possible with current technology. Concurrently, the Korean VLBI Network (KVN) is capable of observing simultaneously at 4 frequencies, with this ability currently being expanded to Yebes in Spain, the KVN and Vera Array (KaVA) and soon, tests with the 100m dish at Effelsberg in Germany and with the Very Long Baseline Array (VLBA).

Unfortunately, the power of these arrays has often been hampered by the logistical difficulties of organising many observatories and the difficulty of calibrating and analysing the data – particularly at high frequencies. Recent developments, however, are beginning to make VLBI more accessible to all astronomers, with automated pipelines to calibrate data, maximum entrepy methods to reconstruct images, wavelet transforms to compute kinematics and Markov Chains to fit Gaussians to the data using closure amplitudes. In this talk I will overview the current state-of-the art in VLBI and what is planned in the near future. I will then overview the results of a multi-year monitoring project of Gamma-ray bright blazars using the GMVA and then discuss the possibilities of using Active Galactic Nuclei and VLBI to test cosmology at redshifts higher than 2.