A new candidate of a cluster of galaxies behind the Galactic plane, AX J145732-5901

Abstract AX J145732-5901 is an unidentified X-ray source discovered in the ASCA Galactic Plane Survey. Its extended nature and heavily absorbed X-ray spectrum suggest that AX J145732-5901 is a cluster of galaxies behind the Galactic plane. However, due to limited photon statistics, the spectral shape was not well examined. Using the results of the Galactic ridge X-ray emission and cosmic X-ray background studies based on the Suzaku observations, we reanalyzed the ASCA data of AX J145732-5901. We confirmed that the source is more extended than the point spread function and the angular size is $14^{\prime }\times 10^{\prime }$. The spectrum was heavily absorbed by interstellar matter equivalent to an $N_{\rm H}$ of ${\sim}10^{23}$ cm$^{-2}$ and the emission line feature was confirmed. The spectrum was represented by a thin thermal plasma model with a temperature of 2.6 keV and a redshift of 0.12. Assuming the redshift value, the X-ray luminosity is calculated to be $2.6\times 10^{44}$ erg s$^{-1}$ in the 1–10 keV energy band. The observational results indicate that AX J145732-5901 is a cluster of galaxies behind the Galactic plane.