ASCA observation of A1674 Original Research Article

We observed a rich but X-ray faint cluster of galaxies A1674 with ASCA. The cluster belongs to richness class 3, but its X-ray luminosity is as low as 5 × 1043 erg/s. ASCA observation of A1674 revealed its low gas temperature of 3 keV and asymmetric profile of the X-ray emission. Moreover, we find its heavy metal abundance is low; we obtained the upper limit of 0.2 for it. We calculate the total mass of the gas, galaxies, and gravitational matter in A1674, and find the cluster has high galaxy/gravitational mass ratio and low gas/gravitational mass ratio, comparing with other clusters. It is strange, at first sight, that the cluster having large amount of metal source (galaxies) like A1689 indicates such a low metal abundance in the X-ray spectrum. However, by inspecting the color-magnitude diagram of the cluster galaxies, we got a hint that the cluster contains small number of elliptical population. If the low elliptical fraction is confirmed, this cluster provides a valuable proof for the widely believed model in which metal in the intra-cluster gas is dominantly produced by the ellipticals, not by spirals.