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Host galaxy effects on the observational properties and evolution of active galactic nuclei

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How do black holes affect host galaxies?

EU-funded scientists shed new light onto the co-evolution of supermassive black holes and their host galaxies through star formation, a connection that has remained a mystery.

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Most galaxies formed early in the Universe's history have intensely luminous cores, powered by supermassive black holes. These so-called active galactic nuclei (AGN) were the topic of the EU-funded project 'Host galaxy effects on the observational properties and evolution of active galactic nuclei' (HGAGN). Researchers used the enormous amount of light across the entire electromagnetic spectrum produced by material falling into the black holes to analyse a large number of extragalactic sources. They discovered 'hidden' AGN, so heavily shrouded by dust that no visible and ultraviolet light escapes and, for this reason, was previously overlooked. To analyse observations of the XMM-Newton mission, the Sloan Digital Sky Survey (SDSS) and the Wide-field Infrared Survey Explorer (WISE), the SEABASs programme was developed. This software tool decomposes energy emissions across a broad range of wavelengths, the spectral energy distribution (SED). Based on Bayesian statistics, SEABASs combines the observations from AGN with synthetic stellar profiles to perform a maximum-likelihood fit to the input data. The software tool has been made freely available to the scientific community here. SEABASs results have shown a vast range of emissions in the X-ray, visible and infrared frequency bands, providing evidence of the different physical processes forming the SEDs. Infrared emissions, in particular, are no stranger to galactic astronomy. Stars form in dusty regions. The dust absorbs starlight and re-emits it in the infrared. Emissions in the infrared from AGN exhibit picks at different wavelengths and have different characteristic temperatures. These differences were used by HGAGN scientists to investigate how they evolve with respect to each other. Over the last decades, it had become clear that black holes co-evolve with the galaxies that host them, but the details of this co-evolution have yet to be elucidated. HGAGN resulted in new evidence of the co-evolution at red shifts larger than 1, but not at smaller distances. The new findings, published in the Astronomy & Astrophysics journal, shed new light on the complicated mechanisms through which AGN interact with their host galaxies. Future observations of AGN at red shifts smaller than 1will likely offer a deeper understanding of the evolution of galaxies.

Keywords

Black holes, galaxies, active galactic nuclei, XMM-Newton, spectral energy distribution

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