ALMA

Fifty-four 12 m and twelve 7 m antennas at 5,000 m on the Chajnantor plateau, correlated as one interferometerinterferometryCombining waves from separate receivers coherently. In radio and optical astronomy, correlating signals from separated telescopes gives the resolution of one as large as their separation. In gravitational-wave detection, a laser Michelson interferometer measures tiny differential changes in its arm lengths. from 35 to 950 GHz on baselinesbaselineThe separation between two antennas of an interferometer, projected onto the plane perpendicular to the source. Long baselines give fine resolution; short ones recover extended emission. up to 16 km. Resolution reaches 4.4 masarcsecond1/3600 of a degree (″). A milliarcsecond (mas) is 10⁻³″ and a microarcsecond (µas) 10⁻⁶″. Atmospheric seeing limits ground telescopes to about 0.5–1″ without adaptive optics. at 950 GHz on the longest baselines, resolving thermal dust continuumcontinuumBroadband emission, such as synchrotron or thermal dust, as opposed to spectral lines. Continuum surveys sum over a wide bandwidth for sensitivity. and molecular-linespectral lineEmission or absorption at a specific frequency from an atomic or molecular transition. Its strength gives abundance and temperature; its Doppler shift gives line-of-sight velocity. emission in protoplanetary discs, star-forming cores and dusty galaxies at high redshiftredshiftz = λ_observed/λ_emitted − 1, the stretching of light by cosmic expansion (or by recession). For distant sources it stands in for distance and look-back time: z ≈ 1 is about 8 Gyr ago, z ≈ 10 about 13.3 Gyr..

Operator

ESO, NSF, NAOJ

Site

Chajnantor Plateau, Chile

Aperture

66 antennas, up to 16 km apart

Passband

35 GHz – 950 GHz

Early science

30 September 2011