NAME:
dens_in_meanmatterdens
PURPOSE:
convert density to units of the mean matter density
INPUT:
vo - velocity unit in km/s
ro - length unit in kpc
H= (default: 70) Hubble constant in km/s/Mpc
Om= (default: 0.3) Omega matter
OUTPUT:
conversion from units where vo=1. at ro=1. to units of the mean matter density
HISTORY:
2014-01-28 - Written - Bovy (IAS)