Letters of Intent received in 2018

LoI 2020-2041
The Cold Interstellar Medium at Fifty Years

Topics

molecular clouds in the Milky Way, galaxies and galactic nuclei;
chemistry;
clouds and cores;
star and planet formation;
Molecules in planetary systems;
Molecules in evolved stars;
instrumentation;

Rationale

Beginning in the mid to late 60s improvements in telescope technology enabled molecular observations which gradually revealed the Cold Universe to astronomers, beginning with OH, water, ammonia and formaldehyde and culminating in the discovery of CO in 1970. While the earlier molecules suggested a significant cold component to the interstellar medium, the discovery of the ubiquity of strong CO emission surprised astronomers. Its widespread emission suggested that the cold dense phase of the interstellar medium was pervasive and significant—at last the cold dense dust which had foiled optical observations could be measured through molecular lines. Not only could the quantity of material be accurately deduced but its kinematics could be traced and its chemistry explored.

Continuing improvements in telescopes have fueled research in the cold interstellar medium. Around 200 molecules have been now detected in the interstellar medium or circumstellar shells; more than five dozen have been detected in extragalactic sources.

Studies of interstellar molecules, particularly CO, have transformed our understanding of the phases and dynamics of the interstellar medium, the initial stages of stellar and planetary evolution, the chemistry of dense and diffuse interstellar and circumstellar matter and of the solar system, the structure of the Milky Way galaxy, and the content and structure of other galaxies, back to the time of deionization in the Early Universe. Molecular variety and abundance has given rise to the new field of Astrochemistry. Spectroscopic studies of CO and other molecules are primary tools for investigating all these topics, which are among the most fundamental and active research areas in astrophysics.

Molecular emission has been detected from extremely remote massive and luminous galaxies, emitted within the first few hundred million years after the Big Bang. Even at this early stage, the observations suggest that supermassive black holes had formed; spectroscopy of their hosts reveals their character and their kinematics.

In this Symposium we will review our understanding of the cold interstellar medium at the half century mark since its exploration began.