Next Section: Evolution of the HI

Local HI: Constraints on the evolution of the HI content of the Universe

F. H. Briggs
Kapteyn Astronomical Institute
fbriggs@astro.rug.nl

Abstract:

Analyses of QSO absorption lines are showing that HI content has evolved over the redshift range z=5 to z= 0. The 21cm line measurements of the z=0 HI content avoid several biases inherent in the absorption line technique, such as the influence of evolving dust content in the absorbers, and will producing a reliable measure to anchor theories of galaxy evolution. Examples of important questions to be addressed by local HI surveys are: (1) is there a significant population of gas-rich galaxies or intergalactic clouds that is missing from the census of optically selected galaxies? (2) is there an adequate reservoir of neutral gas to substantially prolong star formation at its present rate? and (3) are there massive objects of such low HI column density that they can have escaped detection in the ``unbiased'' HI surveys that have been conducted so far?

Keywords: galaxies: distances and redshifts - galaxies: compact
galaxies: formation - radio lines: galaxies

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