A Characterization of the ALMA Phasing System at 345 GHz

TL;DR

This paper characterizes the performance of the ALMA Phasing System at 345 GHz, extending its capabilities for very long baseline interferometry and reporting on tests including a 2018 EHT collaboration.

Contribution

It provides the first detailed assessment of ALMA's phasing system at 345 GHz, enabling higher frequency VLBI observations.

Findings

Successful characterization of APS at 345 GHz

Demonstrated capability for global VLBI at 345 GHz

Supported EHT observations at higher frequencies

Abstract

The development of the Atacama Large Millimeter/submillimeter Array (ALMA) phasing system (APS) has allowed ALMA to function as an extraordinarily sensitive station for very long baseline interferometry (VLBI) at frequencies of up to 230 GHz (~1.3 mm). Efforts are now underway to extend use of the APS to 345 GHz (~0.87 mm). Here we report a characterization of APS performance at 345 GHz based on a series of tests carried out between 2015-2021, including a successful global VLBI test campaign conducted in 2018 October in collaboration with the Event Horizon Telescope (EHT).