Resonance Line Scattering Modifies X‐Ray Surface Brightness of Elliptical Galaxies

The spatial distributions of the density and temperature of hot gases associated with some elliptical galaxies have been derived from X-ray observations made by the ROSAT and ASCA observatories with their high angular and energy resolution. Utilizing the thus-obtained density and temperature distributions already available in the literature, we investigate how resonance line scattering alters the surface brightness profile of line emission. To do this, the radiative transfer equations in spherical geometry are numerically solved by the Λ-iteration method with an acceleration scheme. It is found that resonance line scattering can depress the surface brightness of line emissions from the central region of X-ray-bright elliptical galaxies by as much as ~33% compared with that obtained by ignoring resonance line scattering. Thus, it is expected that the actual density profiles are different from those in the literature and/or that the abundance distributions that have been deduced from X-ray observations are underestimated in the central region and overestimated in the outer region. To deduce the density and temperature distribution of the hot gas of an elliptical galaxy, one should use the continuum photons that suffer no scattering; then the line emission would give the abundance distributions if resonance line scattering is properly taken into account.