| Description: | Cold hydrogen gas, the fuel of star formation, plays a pivotal role in the evolution of galaxies. Direct observation of HI through its 21-cm emission provides morphological and kinematical information about the neutral hydrogen component in and around galaxies. Wide and deep surveys of extragalactic HI are ongoing, and I will give a "survey of surveys", with focus on the suite of Arecibo L-band Feed Array (ALFA) surveys. These current-generation surveys will provide samples of tens of thousands of galaxies, reaching to z~0.1. Existing and near-term facilities will continue to push our knowledge to intermediate redshifts in the coming years, and do pathfinding science work which will feed into the design of the ultimate deep (z>1), high-resolution HI surveys with the Square Kilometer Array. |
