Mertens, Florent

Longitudinal and transverse velocity fields in parsec-scale jets.

Author list: Florent Mertens, Andrei Lobanov

Radio-loud AGN typically manifest powerful realtivistc jets extending up to millions of light years and often showing superluminal motions organized in a complex kinematic pattern.  A number of physical models are still competing to explain the jet structure and kinematics revealed by radio images using the VLBI technique. Robust measurements of longitudinal and transverse velocity field in the jets would provide crucial information for these models. This is a difficult task, particularly for transversely resolved jets in objects like 3C273 and M87. To address this task, we have developed a new technique for identifying significant structural details (SSD) of smooth, transversely resolved flows and obtaining a velocity field from cross-correlation of these regions in multi-epoch observations. Detection of individual SSD is performed using the wavelet decomposition and multiscale segmentation of the observed structure. The cross-correlation algorithm combines structural information on different scales of the wavelet decomposition, providing a robust and reliable identification of related SSD in multi-epoch images. The algorithm enables recovering structural evolution on scales down to ~0.25 FWHM of the image PSF. We present here the results from application of this algorithm to obtaining the first detailed transverse velocity fields and studying the kinematic evolution in the parsec-scale jets in 3C273 and M87.