Neutral hydrogen in the local Universe

Research output: Chapter in Book/Conference paperConference paperpeer-review


We revisit the composition of neutral hydrogen, i.e. atomic (HI) and molecular (H2), in the local Universe, with focus on the H 2-to-HI mass ratio ηgal in various galaxies and the H2-mass function (MF). First, we derive the H2-MF from the CO-luminosity function (LF) of the FCRAO Extragalactic CO Survey, using a variable CO-to-H2 conversion fitted to nearby observations. This implies a universal H2 density ΩH2=(6.9±2.7) 10-5h-1 and ΩH2/HI=0. 26±0.11, which could, however, suffer from incompleteness of the CO-sample. Therefore, a second approach derives the H2-MF from a HI-sample with well described completeness (HIPASS). This premisses an estimation of ηgal, for which we introduce a set of phenomenological models based on a sample of 245 galaxies drawn from the literature. Our best model in terms of statistical scatter describes ηgal as a function of galaxy type and cold gas mass. This model leads to an H2-MF that matches the one derived from the CO-LF, thus supporting that model and settling completeness uncertainties.

Original languageEnglish
Title of host publicationThe Evolution of Galaxies Through the Neutral Hydrogen Window
Number of pages7
Publication statusPublished - 2008
Externally publishedYes
EventThe Evolution of Galaxies Through the Neutral Hydrogen Window - Arecibo, Puerto Rico
Duration: 1 Feb 20083 Feb 2008

Publication series

NameAIP Conference Proceedings
ISSN (Print)0094-243X
ISSN (Electronic)1551-7616


ConferenceThe Evolution of Galaxies Through the Neutral Hydrogen Window
Country/TerritoryPuerto Rico


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