Detection of multiple velocity components in partially overlapping emitting regions

TL;DR

This paper introduces a new wavelet-based method combining stacked cross-correlation to detect and track multiple velocity components in overlapping astrophysical features, improving analysis of complex evolving structures.

Contribution

A novel method integrating wavelet decomposition and stacked cross-correlation for separating and tracking overlapping velocity components in astronomical images.

Findings

Successfully detected multiple velocity components in simulated jets.

Revealed distinct superluminal streams in 3C 273.

Observed flow acceleration in 3C 120.

Abstract

Velocity measurements made from multiple-epoch astronomical images of evolving objects with optically thin continuum emission (e.g. as relativistic jets or expanding supernova shells) may be confused as a result of the overlap of semi-transparent features moving at different speeds. Multi-scale wavelet decomposition can be effectively applied to identify and track such overlapping features, provided that their respective structural responses can be separated over the spatial scales used for the decomposition. We developed a new method that combines the stacked cross-correlation with the wavelet-based image segmentation and evaluation (WISE) technique of decomposition of two-dimensional structures, to separate and track dominant spatial responses of overlapping evolving features. The method is tested on a set of simulated images of a stratified relativistic jet, demonstrating the robust detection of both the faster spine and the slower sheath speeds. The method is applied to mutliple-epoch images from the MOJAVE survey, revealing two different superluminal streams inside the jet in 3C 273 and the acceleration of the flow in 3C 120. The method can be applied to densely monitored objects with composite structural evolution such as the parsec-scale jet in M87 or heavily resolved expanding supernova shells.