The ALMA Phasing System: A Beamforming Capability for Ultra-High-Resolution Science at (Sub)Millimeter Wavelengths

TL;DR

The ALMA Phasing System enables the ALMA array to function as a single large aperture for VLBI, significantly enhancing high-resolution astronomical observations at (sub)millimeter wavelengths.

Contribution

This paper introduces the design, implementation, and performance of the ALMA Phasing System, a novel hardware and software solution for coherent beamforming in VLBI.

Findings

Enhanced sensitivity and resolution in VLBI observations.

Successful deployment of the phased ALMA system.

Enabling new ultra-high angular resolution science applications.

Abstract

The Atacama Millimeter/submillimeter Array (ALMA) Phasing Project (APP) has developed and deployed the hardware and software necessary to coherently sum the signals of individual ALMA antennas and record the aggregate sum in Very Long Baseline Interferometry (VLBI) Data Exchange Format. These beamforming capabilities allow the ALMA array to collectively function as the equivalent of a single large aperture and participate in global VLBI arrays. The inclusion of phased ALMA in current VLBI networks operating at (sub)millimeter wavelengths provides an order of magnitude improvement in sensitivity, as well as enhancements in u-v coverage and north-south angular resolution. The availability of a phased ALMA enables a wide range of new ultra-high angular resolution science applications, including the resolution of supermassive black holes on event horizon scales and studies of the launch and collimation of astrophysical jets. It also provides a high-sensitivity aperture that may be used for investigations such as pulsar searches at high frequencies. This paper provides an overview of the ALMA Phasing System design, implementation, and performance characteristics.