The 2014 ALMA Long Baseline Campaign: An Overview
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 2014 September to late November, 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 3C 138 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.
© 2015 American Astronomical Society. Received 2015 March 9; accepted 2015 April 10; published 2015 July 14. This article is part of the ALMA Long Baseline Campaign collection. An introduction and the full list of articles can be found at http://iopscience.iop. org/2041-8205/page/Focus_on_the_ALMA_Long_Baseline_Campaign. This paper makes use of the following ALMA data: ADS/JAO. ALMA#2011.0.00013.SV, ADS/JAO.ALMA#2011.0.00014.SV, ADS/JAO.ALMA#2011.0.00015.SV, and ADS/JAO. ALMA#2011.0.00016.SV. ALMA is a partnership of ESO (representing its member states), NSF (USA) and NINS (Japan), together with NRC (Canada), NSC and ASIAA (Taiwan), and KASI (Republic of Korea), in cooperation with the Republic of Chile. The Joint ALMA Observatory is operated by ESO, AUI/NRAO and NAOJ. The National Radio Astronomy Observatory is a facility of the National Science Foundation operated under cooperative agreement by Associated Universities, Inc. We thank all those who have contributed to making the ALMA project possible. Facility: ALMA.
Submitted - 1504.04877v2.pdf
Published - 2041-8205_808_1_L1.pdf