Atacama Large Millimeter/submillimeter Array

Atacama Large Millimeter/submillimeter Array
Iztok Bončina/ESO · CC BY 4.0 · source
Name	Atacama Large Millimeter/submillimeter Array
Location	Chajnantor Plateau, Atacama Desert
Altitude	5,000 m
Established	2011
Wavelength	0.3–9.6 mm
Type	Radio interferometer

Atacama Large Millimeter/submillimeter Array is a major international radio observatory located on the Chajnantor Plateau in the Atacama Desert near San Pedro de Atacama, Chile. The facility is a collaboration among institutions from North America, Europe, East Asia, and Chile, and is designed to observe millimeter and submillimeter wavelength emission from cold gas and dust in astrophysical environments. Its capabilities have transformed research in star formation, galaxy evolution, and planetary science by combining high angular resolution with high sensitivity.

Overview

The array comprises 66 high-precision antennas operating as an interferometer on a high, dry site to minimize atmospheric absorption, enabling observations across millimeter and submillimeter bands. Its baseline configurations provide angular resolution comparable to optical telescopes such as the Hubble Space Telescope and complement facilities like the Very Large Telescope, James Webb Space Telescope, and the Karl G. Jansky Very Large Array. The observatory supports programs ranging from targeted proposals by teams at institutions such as the National Radio Astronomy Observatory, European Southern Observatory, and National Astronomical Observatory of Japan to legacy surveys coordinated with projects like the Sloan Digital Sky Survey and missions including Herschel Space Observatory.

History and construction

Planning grew from concepts developed by organizations including the National Science Foundation, the European Organisation for Astronomical Research in the Southern Hemisphere, and Japanese agencies, with roots in earlier projects such as the Owens Valley Radio Observatory upgrades and the Submillimeter Array. Site selection favored the Chajnantor Plateau for its proximity to Cerro Toco and Licancabur, and construction involved logistics comparable to projects like the Atacama Cosmology Telescope and the ALMA Pathfinder. Major milestones included antenna delivery from manufacturers in Japan, Spain, and United States contractors, array commissioning with arrays of increasing antenna counts, and formal inauguration events attended by representatives from Chile, United States of America, Japan, and European partners.

Array design and instrumentation

The facility uses a heterogeneous array model combining 12-meter and 7-meter dishes, with a compact Atacama Compact Array and main array configurations. The correlator, a high-performance digital backend, processes signals akin to systems used at the Very Long Baseline Array and the Event Horizon Telescope collaboration, enabling aperture synthesis imaging and very long baseline interferometry when tied to networks including European VLBI Network partners. Receiver suites cover multiple bands with cryogenic mixers and superconducting technology developed in partnerships with laboratories such as the NRAO Central Development Laboratory and institutions like the Max Planck Institute for Radio Astronomy, National Astronomical Observatory of Japan, and Instituto de Astrofísica de Canarias.

Operations and governance

Operations are governed through a partnership model involving the European Southern Observatory, the National Science Foundation, the National Institutes of Natural Sciences (Japan), and Chilean institutions, with user support provided through regional centers including the North American ALMA Regional Center, the European ALMA Regional Center, and the East Asian ALMA Regional Center. Time allocation processes mirror competitive peer review systems used by organizations like the Hubble Space Telescope Science Institute and the European Southern Observatory’s Observing Programmes Committee. Day-to-day operations rely on engineering teams with expertise comparable to staff at the Green Bank Observatory and the South African Radio Astronomy Observatory.

Scientific contributions and discoveries

Scientific output spans studies of protoplanetary disks in systems such as HL Tauri and detections of complex organic molecules in sources like Sgr B2, measurements of molecular gas in high-redshift galaxies related to surveys by the Atacama Cosmology Telescope and Planck (spacecraft), and imaging of jet-launching regions around young stellar objects comparable to observations of T Tauri stars. ALMA results have influenced models of planet formation and informed observations by missions including Cassini–Huygens, Rosetta (spacecraft), and Kepler (spacecraft), while enabling follow-up of transients discovered by facilities such as the Fermi Gamma-ray Space Telescope and the Zwicky Transient Facility. The array has contributed to multi-messenger campaigns with observatories like LIGO and the European Southern Observatory on counterparts to gravitational-wave events.

Site and environment

The Chajnantor site lies within the Atacama Region near protected areas and indigenous communities, requiring coordination with Chilean authorities such as the Ministry of Foreign Affairs (Chile) and cultural stakeholders including local municipalities around San Pedro de Atacama. Environmental and logistical considerations echo challenges faced by projects on Mauna Kea and Cerro Tololo, including high-altitude health protocols for personnel and infrastructure resilience against extreme aridity and ultraviolet exposure, with support from institutions like Comunidad Indígena representatives and national research agencies.

Future upgrades and developments

Planned upgrades include receiver enhancements, expansion of bandwidth and correlator capacity, and integration with global very long baseline interferometry campaigns including the Event Horizon Telescope and future networks envisioned by consortia involving the Square Kilometre Array Organization and the International Astronomical Union. Science-driven proposals aim to extend sensitivity for molecular line surveys and deep extragalactic imaging to address questions raised by missions such as the James Webb Space Telescope and programs like the Large Synoptic Survey Telescope project, while governance discussions involve partner agencies including the National Science Foundation and European Commission funding mechanisms.

Category:Radio telescopes Category:Observatories in Chile