
TY  - JOUR
A1  - Zwaan, Martin A 
A1  - Briggs, Frank H 
A1  - Verheijen, Marc AW 
T1  - The HI Column Density Distribution Function at z=0: the Connection to Damped Ly alpha Statistics
JF  - Publications of the Astronomical Society of Australia
JO  - Publ. Astron. Soc.  Aust.
Y1  - 1999
VL  - 16
IS  - 1
SP  - 100
EP  - 105
KW  - 
UR  - https://doi.org/10.1071/AS99100 
N2  - We present a measurement of the HI column density distribution function f(N_HI) at the present epoch for column densities > 10^20 cm^-2. These high column densities compare to those measured in damped Ly alpha lines seen in absorption against background quasars. Although observationally rare, it appears that the bulk of the neutral gas in the Universe is associated with these damped Ly alpha systems. In order to obtain a good anchor point at z = 0 we determine f(N_HI) in the local Universe by using 21 cm synthesis observations of a complete sample of spiral galaxies. We show that f(N_HI) for damped Ly alpha systems has changed significantly from high z to the present and that change is greatest for the highest column densities. The measurements indicate that low surface brightness galaxies make a minor contribution to the cross section for HI, especially for N_HI > 10^21 cm^-2. 
ER  -

