ALMA Outreach

The Atacama Large Millimeter Array (ALMA) will be the forefront instrument for studying the cool universe - the relic radiation of the Big Bang, and the molecular gas and dust that constitute the very building blocks of stars, planetary systems, galaxies, and life itself. This material typically resides at temperatures of 3-100 K, resulting in spectral energy distributions peaking at submillimeter through to far-infrared wavelengths. Most of the energy in the Universe lies in two thermal components - the cosmic background and the far infrared background - whose Earth-accessible spectrum lies within the ALMA frequency coverage. Indeed, the peak of the spectral energy distribution for dusty objects in the distant universe becomes redshifted entirely to submillimeter wavelengths. While a number of current and future telescopes will operate at submillimeter wavelengths in order to exploit the wealth of information available in this part of the electromagnetic spectrum, none will have the combination of sensitivity, resolution, and frequency coverage of ALMA.

The power of ALMA will enable new science in many areas, examples of which are highlighted below. The design of the instrument is being driven by three key science goals:

1. The ability to detect spectral line emission from CO or CII in a normal galaxy like the Milky Way at a redshift of z = 3, in less than 24 hours of observation. (C. DeBreuck ppt presentation from "Dusty" Meeting Oct 2004)
2. The ability to image the gas kinematics in protostars and in protoplanetary disks around young Sun-like stars at a distance of 150 pc (roughly the distance of the star-forming clouds in Ophiuchus or Corona Australis), enabling the study of their physical, chemical and magnetic field structures and to detect the tidal gaps created by planets undergoing formation in the disks. (J. Richer ppt presentation from "Dusty" Meeting Oct 2004)
3. The ability to provide images at an angular resolution of 0.01 arcsec, and precise images at an angular resolution of 0.1 arcsec. Here the term "precise image" means being able to represent, within the noise level, the sky brightness at all points where the brightness is greater than 0.1% of the peak image brightness.

These three goals drive the large collecting area, the spectral capabilities, and the number of elements of ALMA, as detailed in ALMA Scientific Specifications and Requirements.

This remarkable instrument will be able to:

• Image the redshifted dust continuum emission from evolving galaxies at epochs of formation as early as z = 10. The inverse K-correction on the Rayleigh-Jeans side of the spectral energy distribution of a dusty galaxy compensates for dimming at high redshift, making ALMA the ideal instrument for investigating the origins of galaxies in the early universe, with confusion minimized by the high spatial resolution. (A. Blain ppt presentation from UMd ALMA Workshop May 2004)
• Use the emission from CO to measure the redshift of star-forming galaxies throughout the universe. The spacing between successive transitions of CO shrinks with redshift as (1 + z), and the large instantaneous total bandwidth of ALMA will make possible blind surveys in order to establish the star-forming history of the universe, without the uncertainties inherent in optical and UV studies caused by dust extinction.
• Probe the cold dust and molecular gas in nearby galaxies, allowing detailed studies of the interstellar medium in different galactic environments, the effect of the physical conditions on the local star formation history, and galactic structure. The resolution of ALMA will reveal the kinematics of obscured active galactic nuclei and quasars on spatial scales of 10-100 pc, and will be able to test unification models of Seyfert galaxies.
• Image the complex dynamics of the molecular gas at the center of our own Galaxy with unprecedented spatial resolution, thereby revealing the tidal, magnetic, and turbulent processes that make stellar birth and death at the Galactic Center more extreme than in the local Solar neighborhood.
• Reveal the details of how stars form from the gravitational collapse of dense cores in molecular clouds. The spatial resolution of ALMA will allow the accretion of cloud material onto an accretion disk to be imaged, and will trace the formation and evolution of disks and jets in young protostellar systems. For older protostars and pre-main sequence stars ALMA will show how planets form, sweeping gaps in circumstellar and debris disks. (N. Evans ppt presentation from UMd ALMA Workshop May 2004)
• Uncover the chemical composition of the molecular gas surrounding young stars, including establishing the role of the freeze-out of gas-phase species onto grains, the re-release of these species back into the gas phase in the warm inner regions of circumstellar disks, and the subsequent formation of complex organic molecules. ALMA will have the large total bandwidth, high spectral resolution, and sensitivity needed to detect the myriad of lines associated with heavy, pre-biotic molecules such as those which may have been present in the young Solar System.
• Image the formation of molecules and dust grains in the circumstellar shells and envelopes of evolved stars, novae, and supernovae. ALMA will resolve the crucial isotopic and chemical gradients within these circumstellar shells, which reflect the chronology of the invisible stellar nuclear processing. (M. Meixner ppt presentation from UMd ALMA Workshop May 2004)
• Refine dynamical and chemical models of the atmospheres of planets in our own Solar System, and provide unobscured images of cometary nuclei, hundreds of asteroids, Centaurs, and Kuiper Belt Objects. (M. Gurwell ppt presentation from UMd ALMA Workshop May 2004)