Development Plans for the Atacama Large Millimeter/submillimeter Array (ALMA)

The Atacama Large Millimeter/submillimeter Array (ALMA) was the top-ranked priority for a new ground-based facility in the 2000 Long Range Plan. Ten years later, at the time of LRP2010, ALMA construction was well underway, with first science observations anticipated for 2011. In the past 8 years, ALMA has proved itself to be a high-impact, high-demand observatory, with record numbers of proposals submitted to the past few annual calls (more proposals than are submitted annually to HST) and large numbers of highly cited scientific papers across fields from protoplanetary disks to high-redshift galaxies and quasars. Since Cycle 4, ALMA has also begun to carry out large programs using more than 60 hours of observing time on the 12-m array or more than 200 hours of time on the Atacama Compact Array (ACA).

ALMA’s scientific impact reaches into nearly every area of astronomy. Highlights include the first image of a supermassive black hole in the centre of M87 by the Event Horizon Telescope Collaboration; Canadians led the analysis that extracted the physics, such as black hole mass and spin, from that image. A Canadian-led collaboration has shown that radio galaxies located in clusters and groups can drive molecular gas flows (both inflows and outflows) up to 10s of kpc in altitude. Canadians are also leading innovative studies of proto-stellar and proto-planetary disks, including the first systematic study of their morpohologies and the location of gaps that can signal unseen planets. VERTICO (PI. T. Brown) is the first Canadian-led ALMA large program. VERTICO will map 51 spiral galaxies in the nearby Virgo cluster and use a multi-wavelength approach to quantify the effect of cluster environment on the star-forming molecular gas.

The LRP2010 ALMA white paper laid out 8 specific metrics for ALMA and the Canadian ALMA user community that could be used to judge the success of Canada’s participation in ALMA.  These metrics ranged from publications (number; impact) to collaborations (international; multi-wavelength) to student training and leadership in ALMA operations, as well as the successful completion of the Band 3 (3mm, 100 GHz) receivers and ALMA development projects. All 8 metrics argue for Canada’s involvement in ALMA over the past decade to be judged a success. The successful achievement of these wide-ranging goals argues strongly for Canada’s continuing participation in operating and developing ALMA over the next decade and beyond.

To call out one particular success metric, Canadians are making excellent use of ALMA in training graduate students and postdocs. For example, 12 of 23 Canadian first-author papers published as of June 2018 were led by a graduate student, and a further 4 papers were led by postdocs. As of that date, the Canadian-led paper with the highest number of citations was by a graduate student. The first Canadian-led ALMA large program (VERTICO) is led by postdoc T. Brown at McMaster University.

The ALMA observatory has identified a set of short and medium-term development goals that will keep ALMA at the cutting-edge of astronomy and allow it to continue producing transformational scientific results in future decades. Over the next decade, the focus is on expanding the spectral bandwidth of ALMA by a factor of at least two. This increase in bandwidth requires upgrades to ALMA’s receivers, electronics, and correlator. These increases in bandwidth will reduce the integration time required for a variety of scientific programs, such as blind redshift surveys, spectral scans, and sensitive continuum imaging, by a factor of two. High-resolution spectral scans, for example of proto-planetary disks, will see an increase in speed by a factor of 8 or more. Improvements to the ALMA Archive is another important focus, particularly in the area of applying data mining to large spectral datasets. There are opportunities for Canadian participation and/or leadership in many of these development areas.

Looking forward to the next decade of ALMA operations, our community needs to:

1. maintain Canadian access to ALMA and our competitiveness in using ALMA;
2. preserve full Canadian funding for our share of ALMA operations;
3. identify components of ALMA development in which Canada can play a significant role, including stimulating expertise in submillimetre instrumentation to capitalize on future opportunities; and
4. keep Canadians fully trained and engaged in ALMA, as new capabilities become available, reaching the widest possible community of potential users.