January 13, 2016

martha haynesMartha Haynes
Cornell University
Ithaca, NY

A Renaissance in Surveys of Gas in Galaxies: From ALFA to the Future

Abstract

Ever since its detection in the Milky Way by Ewen and Purcell in 1951, the ground-state “spin-flip” 21 cm line of atomic hydrogen (HI) has been used by radio astronomers to probe the cool-to-warm gas in the interstellar medium of galaxies. Exploiting the huge collecting area of the Arecibo 305 meter antenna, the ALFALFA HI line survey has mapped 7000 square degrees of sky, cataloging ~30,000 HI line sources, and for the first time, covering a cosmologically-significant volume of the local universe. Virtually all star-forming galaxies contain a cool neutral component of their interstellar medium, representing the fuel reservoir from which stars may form in the future.

In this talk, I will review the relationship between galaxy populations traced by optical/IR and radio HI line surveys, the differences in their clustering properties, and the importance of HI-selected samples in contributing to the understanding of apparent conflicts between observation and theory on the abundance of low mass dark matter halos. I will also give an overview of planned Square Kilometre array pathfinder surveys which will explore the cosmic evolution of properties of the HI population.