We derive a non-parametric CO luminosity function using a FIR and an optical B -band selected sample of the galaxies included in the FCRAO Extragalactic CO Survey .
The FIR selected sample is defined using the IRAS Bright Galaxy Surveys ( BGS ; IRAS 60 micron flux density \geq 5.24 Jy ) .
Although our CO sample is not complete , the normalization using the BGS reproduces the IRAS 60 micron luminosity function in excellent agreement with those found in the literature .
Similarly , a B -band selected sample defined using the Revised Shapley-Ames ( RSA ) catalog is used to derive a CO luminosity function for a comparison .
A Schechter function describes the both derived CO luminosity functions reasonably well .
Adopting the standard CO-to-H _ { 2 } conversion factor , we derive a molecular gas density of \rho _ { H _ { 2 } } = ( 3.1 \pm 1.2 ) \times 10 ^ { 7 } hM _ { \odot } Mpc ^ { -3 } for the local volume .
Combining with the measurements of the local HI mass density and the helium contribution , we estimate that the total mass density of cold neutral gas in the local universe is \Omega _ { gas } = ( 4.3 \pm 1.1 ) \times 10 ^ { -4 } h ^ { -1 } , which is about 20 % of the total stellar mass density \Omega _ { * } .