Observation of the Cluster of Galaxies MS 0839 . 9 + 2938 at z = 0 . 194 : the Central Excess Iron and SN Ia Enrichment

We present the Chandra study of the intermediately distant (z = 0.194) cluster of galaxies MS 0839.9+2938. By performing both the projected and deprojected spectral analyses, we find that the gas temperature is approximately constant at about 4 keV in 130 − 444h 70 kpc. In the inner regions, the gas temperature descends towards the center, reaching < ∼ 3 keV in the central 37h 70 kpc. This infers that the lower and upper limits of the mass deposit rate are 9−34M⊙ yr and 96−126M⊙ yr, respectively within 74h 70 kpc where the gas is significantly colder. Along with the temperature drop, we detect a significant inward iron abundance increase from about 0.4 solar in the outer regions to ≃1 solar within the central 37h 70 kpc. Thus MS 0839.9+2938 is the cluster showing the most significant central iron excess at z ∼ 0.2. We argue that most of the excess iron should have been contributed by SNe Ia. By utilizing the observed SN Ia rate and stellar mass loss rate, we estimate that the time needed to enrich the central region with excess iron is 6.4 − 7.9 Gyr, which is similar to those found for the nearby clusters. Coinciding with the optical extension of the cD galaxy (up to about 30h 70 kpc), the observed X-ray surface brightness profile exhibits an excess beyond the distribution expected by either the β model or the NFW model, and can be well fitted with an empirical two-β model that leads to a relatively flatter mass profile in the innermost region. Subject headings: galaxies: clusters: individual (MS 0839.9+2938) — intergalactic medium — galaxies: evolution — X-rays: galaxies: clusters Department of Physics, Shanghai Jiao Tong University, 1954 Huashan Road, Shanghai 200030, PRC; E-mail: [email protected], [email protected] National Astronomical Observatories, Chinese Academy of Sciences, 20A Datun Road, Beijing 100012, PRC; E-mail: [email protected], [email protected], [email protected] Department of Astronomy, Beijing Normal University, 19 Xinjiekouwai Street, Beijing 100875, PRC