HGAGN

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

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 Obiettivo del progetto (Objective)

'The purpose of the proposed project is to study the host galaxies of active galactic nuclei. AGN are considered to be among the most energetic processes in the universe and are thought to affect the evolution of galaxies. Because of their vast energy release they often outshine their host galaxies, so the study of the AGN-host system can be very challenging. Here, we propose a multi-wavelength approach, taking advantage of the fact that different physical processes leave their characteristic signatures in different parts of the spectrum, for example hot gas being accreted onto the AGN dominates the X-rays and UV light, while star formation and stellar emission of the host galaxy have their peaks in the far-infrared and optical bands respectively. We are planning to use a sample of AGN from the regions of the sky with the deepest coverage in virtually all bands, the Chandra deep fields. New telescopes and instruments like NuSTAR, SCUBA-2, and Herschel, for which the host institute will guarantee data flow, will provide an unprecedented multi-wavelength dataset and we plan to develop new SED fitting methods to exploit it. SED fitting is one of the most promising methods to disentangle AGN and host galaxy properties, and it uses combinations of template SEDs (spectral energy distributions, i.e. broad-band spectra) of different physical processes to reproduce the observed spectrum. We plan to expand on a code developed by the researcher and ultimately make it available to the astronomical community. The results will be used to study the coeval growth of the AGN and its host, taking into account information on different processes taking place, and their interactions. This will help us understand the importance of AGN for the development of the structures we observe in the universe today.'

Introduzione (Teaser)

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.

Descrizione progetto (Article)

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 http://astro.dur.ac.uk/~erovilos/SEABASs/ (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.