Science with ALMA: Cosmology Extragalactic

For more details, see the:

• MMA Report of the Cosmology & Extragalactic Working Group
• Science with the LSA/MMA - Early Universe Studies

The Early Universe

Star-forming galaxies will be detectable out to z = 20 because of the large negative K-correction in the far-infrared dust emission peak. This may be the best way to find the first galaxies in the "dark ages" beyond z = 5, and the star-forming galaxies invisible to HST and VLT because of dust obscuration. (Sub)millimeter observations are essential to our understanding of the star-formation history of the Universe. The "ladder" of molecular transitions essentially guarantees that a redshifted line will appear in one of the observing bands. Millimeter continuum and line emission has already been detected in some of the most distant objects known, at redshifts near 5.

Gravitational Lenses

Many gravitational lenses may be found - possibly more numerous and at higher redshifts than in the optical or radio wavebands because of the very steep source count. Gravitational arcs will be mapped in molecular lines.

Quasar Absorption Lines

Quasar molecular absorption lines will be observed in the spectra of many sources. This is a new field with great potential, which was recently pioneered at the SEST. Over 30 molecular transitions have already been detected in individual absorption systems up to z = 0.9. In such systems one can study detailed chemistry at cosmological distances, the microwave background temperature vs. redshift, and gravitational lens time delays. The high sensitivity of the ALMA will make a large number of distant sources accessible.

Active Galactic Nuclei

AGN can be studied "in depth", because of the low synchrotron and dust opacity and the unprecedented angular resolution of millimeter VLBI. The ALMA will provide millijansky VLBI sensitivity, corresponding to brightness temperatures as low as 100-10000 K. The optically-obscured molecular tori and the circumnuclear starbursts of nearby galaxies can be resolved. The presence of central black holes can be studied kinematically in a large number of galaxies.

Normal Galaxies

The ALMA will make observations of normal galaxies at z = 1-2 with the same detail as is presently possible in nearby galaxies. The main dynamical features of nearby spirals will be resolved with enough resolution and sensitivity to constrain theoretical scenarios of galaxy evolution. The mass spectrum of molecular clouds in galaxies of different types will be determined.

Magellanic Clouds

In the Magellanic Clouds, large statistical samples of many types of objects at essentially the same distance can be studied and compared in detail with the corresponding objects in the Galaxy: molecular clouds, star-forming regions, SiO masers, circumstellar shells, supernova remnants.