The Fe Kα emission line in water megamaser galaxies

Water maser emissions at around 22 GHz from extragalactic sources are significant in astrophysics, offering a unique means to measure cosmological distances and thus constrain the Hubble parameter with high precision. They also provide the most precise method for measuring black hole masses beyond the Milky Way. The challenge of their limited detection has spurred researchers to seek clues for better characterisation. Despite these efforts, the physical environments in which these masers form still need to be clarified. Consequently, statistical studies have been extensively employed to enhance our understanding of these environments. A sample of 32 Active Galactic Nuclei (AGN)-powered water megamaser galaxies and their Fe K alpha emission line at 6.4 keV data was compiled and statistically analysed to investigate any correlation between the two parameters for the first time. A Spearman correlation analysis shows a statistically significant inverse correlation between the maser luminosity (L-22 GHz) and the Fe K alpha luminosity (L-Fe K alpha). Specifically, Spearman's coefficient rho was -0.48, with a p-value = 5 x 10(-3). This anti-correlation suggests that in luminous X-ray galaxies, AGN feedback may heat the circumnuclear clouds, leading to more substantial maser emissions, as it favours warm gas while weakening Fe K alpha, which is associated with cold, dense gas environments. Additionally, the obscuration and orientation of the AGN's circumnuclear material play a significant role, with denser, edge-on tori potentially favouring maser production while diluting Fe K alpha emission. The lack of significant correlations between L-22 GHz and other AGN indicators, such as absorption-corrected L2-10 keV and L-12 mu, combined with the previously found anti-correlation between L-Fe K alpha and these indicators suggest that the observed L-22 GHz-L-Fe K alpha anti-correlation is driven by localised effects within the masing region rather than broader AGN properties. These findings highlight the need for further research with larger samples and more detailed modelling to disentangle the various factors influencing maser activity in AGN environments and validate the anticorrelation's significance, as sources of uncertainty might still have affected the results. (c) 2024 COSPAR. Published by Elsevier B.V. All rights are reserved, including those for text and data mining, AI training, and similar technologies.