A NEW MEASUREMENT OF THE BARYONIC FRACTION USING THE SPARSE NGC-3258 GROUP OF GALAXIES

New X-ray observations of the sparse NGC 3258 group of galaxies made b y the ASCA satellite with good spectral and spatial resolution has rev ealed that this group has a gravitational potential deep enough to pro hibit significant mass removal from the system. The baryonic fraction within 240 h(50)(-1) kpc is found to be 0.065(-0.020)(+0.051) for h(50 ) = 1, where h(50) = H-0/50 km s(-1) Mpc(-1), in good agreement with t he universal value of 0.05 +/- 0.01 predicted by standard big bang nuc leosynthesis for a universe with Omega(0) = 1 and h(50) = 1. Since the deep potential of the NGC 3258 group ensures that all pristine intrag roup gas has been retained, the baryonic fraction of the NGC 3258 grou p is indicative of the universal value. Consequently, it seems prematu re to rule out a critical universe.