@article{10902/28465,
year = {2023},
url = {https://hdl.handle.net/10902/28465},
abstract = {A complete census of active galactic nuclei (AGNs) is a prerequisite for understanding the growth of supermassive black holes across cosmic time. A significant challenge towards this goal is the whereabouts of heavily obscured AGN that remain uncertain. This paper sets new constraints on the demographics of this population by developing a methodology that combines X-ray spectral information with priors derived from multiwavelength observations. We select X-ray AGN in the Chandra COSMOS Legacy survey and fit their 2.2−500μm
 spectral energy distributions with galaxy and AGN templates to determine the mid-infrared (⁠6μm⁠) luminosity of the AGN component. Empirical correlations between X-ray and 6μm
 luminosities are then adopted to infer the intrinsic accretion luminosity at X-rays for individual AGN. This is used as prior information in our Bayesian X-ray spectral analysis to estimate physical properties, such as line-of-sight obscuration. Our approach breaks the degeneracies between accretion luminosity and obscuration that affect X-ray spectral analysis, particularly for the most heavily obscured (Compton-Thick) AGN with low photon counts X-ray spectra. The X-ray spectral results are then combined with the selection function of the Chandra COSMOS Legacy survey to derive the AGN space density and a Compton-Thick fraction of 21.0+16.1−9.9 per cent at redshifts z < 0.5. At higher redshift, our analysis suggests upper limits to the Compton-Thick AGN fraction of ≲40 per cent⁠. These estimates are at the low end of the range of values determined in the literature and underline the importance of multiwavelength approaches for tackling the challenge of heavily obscured AGN demographics.},
organization = {We thank the anonymous referee for their comments and suggestions. This work has been supported by the EU H2020-MSCA-ITN-2019 Project 860744 ‘BiD4BESt: Big Data applications for black hole Evolution STudies.’ This research made use of ASTROPY,4 a community-developed core PYTHON package for Astronomy (Astropy Collaboration 2013, 2018). This research has made use of data obtained from the Chandra Data Archive and the Chandra Source Catalog, and software provided by the Chandra X-ray Center (CXC) in the application packages CIAO and SHERPA. For analysing X-ray spectra, we use the analysis software BXA (Buchner et al. 2014), which connects the nested sampling algorithm ULTRANEST (Buchner 2021) with the fitting environment CIAO/SHERPA (Fruscione et al. 2006).
DMA and DJR acknowledges the Science Technology and Facilities Council (STFC) for support through grant no. ST/T000244/1.
JA acknowledges support from a UKRI Future Leaders Fellowship (grant no.MR/T020989/1).
FJC acknowledges financial support from the Spanish Ministry MCIU under project RTI2018-096686-B-C21 (MCIU/AEI/FEDER/UE), cofunded by FEDER funds and from the Agencia Estatal de Investigación, Unidad de Excelencia María de Maeztu, ref. MDM-2017-0765.
AL is partly supported by the PRIN MIUR 2017 prot. 20173ML3WW 002 ‘Opening the ALMA window on the cosmic evolution of gas, stars, and massive black holes’.
CRA acknowledges support from the projects ‘Feeding and feedback in active galaxies’, with reference PID2019-106027GB-C42, funded by MICINN-AEI/10.13039/501100011033, ‘Quantifying the impact of quasar feedback on galaxy evolution’, with reference EUR2020-112266, funded by MICINN-AEI/10.13039/501100011033 and the European Union NextGenerationEU/PRTR, and from the Consejería de Economía, Conocimiento y Empleo del Gobierno de Canarias and the European Regional Development Fund (ERDF) under grant ‘Quasar feedback and molecular gas reservoirs’, with reference ProID2020010105, ACCISI/FEDER, UE.},
publisher = {Oxford University Press},
publisher = {Monthly Notices of the Royal Astronomical Society, 2023, 518(2), 2546-2566},
title = {The demographics of obscured AGN from X-ray spectroscopy guided by multiwavelength information},
author = {Laloux, Brivael and Georgakakis, Antonis and Andonie, Carolina and Alexander, David M. and Ruiz, Angel and Rosario, David J. and Aird, James and Buchner, Johannes and Carrera Troyano, Francisco Jesús and Lapi, Andrea and Ramos Almeida, Cristina and Salvato, Mara and Shankar, Francesco},
}