An Overview of the 2014 ALMA Long Baseline Campaign

TL;DR

The 2014 ALMA Long Baseline Campaign demonstrated the capability to achieve 19 milliarcsecond resolution at submillimeter wavelengths, enabling high-resolution imaging and establishing new possibilities for submm astronomy.

Contribution

This paper provides a comprehensive overview of the 2014 ALMA Long Baseline Campaign, including testing procedures, calibration, imaging results, and observing strategies for long baselines.

Findings

Achieved angular resolutions as fine as 19 mas at ~350 GHz.

Validated ALMA's capability to observe with baselines up to 15 km.

Demonstrated agreement between ALMA and VLA measurements within a few percent.

Abstract

A major goal of the Atacama Large Millimeter/submillimeter Array (ALMA) is to make accurate images with resolutions of tens of milliarcseconds, which at submillimeter (submm) wavelengths requires baselines up to ~15 km. To develop and test this capability, a Long Baseline Campaign (LBC) was carried out from September to late November 2014, culminating in end-to-end observations, calibrations, and imaging of selected Science Verification (SV) targets. This paper presents an overview of the campaign and its main results, including an investigation of the short-term coherence properties and systematic phase errors over the long baselines at the ALMA site, a summary of the SV targets and observations, and recommendations for science observing strategies at long baselines. Deep ALMA images of the quasar 3C138 at 97 and 241 GHz are also compared to VLA 43 GHz results, demonstrating an agreement at a level of a few percent. As a result of the extensive program of LBC testing, the highly successful SV imaging at long baselines achieved angular resolutions as fine as 19 mas at ~350 GHz. Observing with ALMA on baselines of up to 15 km is now possible, and opens up new parameter space for submm astronomy.