Heavy Element Analysis of X-Ray Faint Elliptical Galaxies

Abstract

Past ASCA and ROSAT observations could not support the general view that elliptical galaxies are sources of metals in the intracluster medium, since observational results have shown that X-ray faint elliptical galaxies exhibit too low metal abundances of hot interstellar medium (ISM). We investigated the radial profiles of the temperature and abundance of 9 X-ray faint elliptical galaxies using the Chandra data. It is found that the heavy element abundance is as high as ∼0.7 solar at the central region. Moreover, toward the periphery of galaxies, the metallicity sharply declines. Therefore, the existence of low-metallicity intergalactic gas around X-ray faint elliptical galaxies is indicated. We also investigated the abundance ratios among several elements of 5 X-ray faint elliptical galaxies using the XMM-Newton data, and obtained a hint that the O/Fe ratio of X-ray faint elliptical galaxies is smaller than that of X-ray bright elliptical galaxies. This result perhaps indicates that, in X-ray faint elliptical galaxies, the contribution of SNeIa is smaller than that in X-ray bright ones, and it is speculated that many of the metals in ISM of X-ray faint elliptical galaxies have escaped into the surrounding space.