ALMA: An Overview

alma 7 antenni Image courtesy ALMA (ESO/NAOJ/NRAO).

Upon completion, the Atacama Large Millimeter Array (ALMA) will be composed of at least 66 high-precision antennae. The array is located on the Chajnantor plain of the Chilean Andes, a site that offers the exceptionally dry and clear sky required to operate at millimeter and submillimeter wavelength. The quality of the observing site, combined with the unprecedented combination of sensitivity, angular resolution, spectral resolution and image fidelity made possible with ALMA, will enable astronomers to carry out transformational research in a wide variety of astronomical areas. The wavelengths covered by ALMA range from 0.3 mm to 3.6 mm (frequency coverage of 84 GHz to 950 GHz) - this range is essential for probing the first stars and galaxies, directly imaging the disks in which planets are formed, and probing the energy output from active supermassive black holes in extremely luminous starburst galaxies.

A brief introduction to ALMA and ALMA observing is given in the document Observing with ALMA: A Primer, developed by our North American ALMA partners from NRC-HIA and the University of Calgary.

The specific level one science goals for the completed ALMA array are:

  • The ability to detect spectral line emission from CO or C+ in a normal galaxy like the Milky Way at a redshift of z = 3, in less than 24 hours of observation.

  • The ability to image the gas kinematics in a solar-mass protostellar/ protoplanetary disk at a distance of 150 pc (roughly, the distance of the star-forming clouds in Ophiuchus or Corona Australis), enabling one to study the physical, chemical, and magnetic field structure of the disk and to detect the tidal gaps created by planets undergoing formation.

  • The ability to provide precise images at an angular resolution of 0.1″. Here the term "precise image" means an accurate representation of the sky brightness at all points where the brightness is greater than 0.1% of the peak image brightness. This requirement applies to all sources visible to ALMA that transit at an elevation greater than 20 degrees.

ALMA will be a complete astronomical imaging and spectroscopic instrument for the millimeter/submillimeter regime, providing scientists with capabilities and wavelength coverage that complement those of other research facilities of its era, such as the Expanded Very Large Array (EVLA), James Webb Space Telescope (JWST), Thirty Metre Telescope (TMT), European Extremely Large Telescope (E-ELT), and Square Kilometer Array (SKA). Specifically, ALMA will fill in a crucial scientific gap by providing a sensitive, high-resolution probe of the cold gas and dust properties of star-forming region in our Galaxy and other galaxies out of high-redshift, and in protoplanetary disks. These region are obscured at shorter wavelengths, thus ALMA complements shorter wavelengths observations by providing a complete picture of these cold regions in which stars and planets are formed.

The Quick Reference Guide summarizing the specifications and observational parameters of ALMA at Early Science (2011) relative to ALMA at Inauguration (2012) is provided on the Early Science Webpage.

Support for the North American community will be provided by the NRAO North American ALMA Science Center in Charlottesville, Virginia, with the assistance of the Herzberg Institute of Astrophysics.

Staff  |   Policies  |   Diversity