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:
- 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)
- 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)
- The ability to provide 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)
More information on the scientific capabilities
of ALMA can be found at the following locations:
