Not –So-Dense Gas in Not-So-Distant Galaxies

Andrew Baker (Rutgers University) 

To understand how galaxies evolve across cosmic time, we must

understand not only their dark matter and their stars, but also the

properties of their interstellar gas, from which new stars form and

into which old stars release the products of their nucleosynthesis.

In normal galaxies like the Milky Way, a majority of this gas lies at

temperatures that are neither hot enough to ionize hydrogen atoms

nor cold enough to permit the formation of hydrogen molecules. Such

material is best traced at radio wavelengths using the 21cm spin-flip

transition of neutral atomic hydrogen (HI). I will describe what we

can learn from observations of HI emission in galaxies, and how we

will use a powerful new array of 64 radio telescopes in South Africa

to observe a single position on the sky for thousands of hours,

thereby probing the evolution of galaxies' HI reservoirs over the

last nine billion years. This effort, constituting the LADUMA (Looking

At the Distant Universe with the MeerKAT Array) survey, will benefit

from close connections with optical-wavelength observations and

theoretical modeling.