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A new method to determine X-ray luminosity functions of AGN and their evolution with redshift

Alqasim, A; Page, MJ; (2023) A new method to determine X-ray luminosity functions of AGN and their evolution with redshift. Monthly Notices of the Royal Astronomical Society , 520 (3) pp. 3827-3846. 10.1093/mnras/stad007. Green open access

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Abstract

Almost all massive galaxies today are understood to contain supermassive black holes (SMBH) at their centres. SMBHs grew by accreting material from their surroundings, emitting X-rays as they did so. X-ray luminosity functions (XLFs) of active galactic nuclei (AGN) have been extensively studied in order to understand the AGN population’s cosmological properties and evolution. We present a new fixed rest-frame method to achieve a more accurate study of the AGN XLF evolution over cosmic time. Normally, XLFs are constructed in a fixed observer-frame energy band, which can be problematic because it probes different rest-frame energies at different redshifts. In the new method, we construct XLFs in the fixed rest-frame band instead, by varying the observed energy band with redshift. We target a rest-frame 2–8 keV band using XMM-Newton and HEAO 1 X-ray data, with seven observer-frame energy bands that vary with redshift for 0 < z < 3. We produce the XLFs using two techniques; one to construct a binned XLF, and one using a maximum likelihood (ML) fit, which makes use of the full unbinned source sample. We find that our ML best-fitting pure luminosity evolution results for both methods are consistent with each other, suggesting that performing XLF evolution studies with the high-redshift data limited to high-luminosity AGN is not very sensitive to the choice of fixed observer-frame or rest-frame energy band, which is consistent with our expectation that high-luminosity AGN typically show little ABSORPTION. We have demonstrated the viability of the new method in measuring the XLF evolution.

Type: Article
Title: A new method to determine X-ray luminosity functions of AGN and their evolution with redshift
Open access status: An open access version is available from UCL Discovery
DOI: 10.1093/mnras/stad007
Publisher version: https://doi.org/10.1093/mnras/stad007
Language: English
Additional information: © 2023 The Author(s) Published by Oxford University Press on behalf of Royal Astronomical Society. This is an Open Access article distributed under the terms of the Creative Commons Attribution License (https://creativecommons.org/licenses/by/4.0/).
Keywords: methods: data analysis, galaxies: active, quasars: supermassive black holes, galaxies: luminosity function, galaxies: nuclei, X-rays: galaxies
UCL classification: UCL
UCL > Provost and Vice Provost Offices > UCL BEAMS
UCL > Provost and Vice Provost Offices > UCL BEAMS > Faculty of Maths and Physical Sciences
UCL > Provost and Vice Provost Offices > UCL BEAMS > Faculty of Maths and Physical Sciences > Dept of Space and Climate Physics
URI: https://discovery.ucl.ac.uk/id/eprint/10171006
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