Radiation field effect on the Fe plasma spectra in the Perseus cluster core.

Abstract

In 2016, x-ray microcalorimeter spectroscopy with the Hitomi soft x-ray spectrometer observed strong spectrum lines of Fe XXIV-XXVI in galaxy NGC 1275 at the center of the Perseus cluster of galaxies. Special attention was paid to the Kα lines of the Fe plasmas [Aharonian et al., Nature (London) 535, 117 (2016)0028-083610.1038/nature18627]. The dominant spectral component was treated as a collisional ionization equilibrium plasma using the SPEX code. However, it was found that the ratio of Fe XXV Heα resonant and forbidden lines is lower than the observed one. This difference could be attributed to the insufficient consideration of radiation field effects in the spectral modeling approach. To address this issue, we recalculated the emission spectra under astrophysical conditions using the nonlocal thermodynamic equilibrium collisional-radiative code. Our analysis reveals a pronounced sensitivity of the emission spectra to the radiative temperature and distribution. Furthermore, we performed a detailed investigation of the atomic processes involving photon interactions and their effects on the emission spectra of Fe plasmas. The recalculated spectra show excellent agreement with the measured spectra, highlighting the significant role of the radiation field in shaping the spectral characteristics of astrophysical plasmas.