1999ApJ...514..765S

We have observed the X-ray-faint, early-type galaxy NGC 3923 with the X-ray satellite ASCA. The observed images were restored using the Richardson-Lucy algorithm. The total mass of hot gas and the total mass of Fe in the halo have been derived from the restored images. We found that NGC 3923 contains a very small amount of hot gas and Fe compared with X-ray-bright early-type galaxies.

The observed mass of the hot gas, M_gas=5.7x10⁷ M_☉, can be produced in 0.063 Gyr by the stellar mass loss; the observed mass of Fe, M_Fe=1.2(0.71-2.2)x10⁵M_☉, can be produced in 0.027 Gyr by Type Ia supernovae. From the short timescales that are inferred, we conclude that NGC 3923 must be in the outflow phase at present.

We show that most early-type galaxies are in their outflow phase at present and that the dynamical accretion of gas clouds, which has been expected from the hierarchical clustering theory, is necessary to explain the observed Fe abundances of early-type galaxies. The outflow driven by Type Ia supernovae and gas accretion due to the dynamical interaction of dark matter clouds produce a large-scale circulation of intergalactic matter.