ALMA and Reionization

ALMA is presenting a huge opportunity to find and study the very faintest targets, including the most distant galaxies. However, ALMA usually detects radiation reprocessed by metals, and thus requires that the debris from the first stars has polluted the interstellar and intergalactic mediums. The very first dusty objects should be revealed, although their surface brightness will be low. The 'negative K-correction' enjoyed by millimeter-wave observers continues to support ALMA users out to red shifts z > 10, but at great distances the cosmic microwave background (CMB) radiation imposes a minimum temperature. As a result, the favorable effect has a limit, and it also imposes a fixed color on the continuum radiation from the most distant objects regardless of redshift. Primordial molecules, shocked molecular hydrogen, perhaps even Hell, hydrogen recombination lines and high-n line series could provide insight into the environment, infall and outfall in the most massive, early protogalaxies. Denser ionized gas offers to be possibly visible via the Sunyaev Zeldovich (SZ) effect, with its a very characteristic spectral signature, and a surface brightness that is independent of redshift. Competing with and complementing James Webb Space Telescope (JWST) in the near- and mid-infrared (IR), Extremely Large Telescopes (ELTs) in the near-IR and the Square Kilometer Array (SKA) and its precursors in the radio, ALMA can enjoy a useful role in keeping a look out for reionizing galaxies in the archive of deep observations, enabled by its unprecedented, excellent sensitivity and spatial resolution.