Issue |
A&A
Volume 686, June 2024
|
|
---|---|---|
Article Number | A223 | |
Number of page(s) | 11 | |
Section | Extragalactic astronomy | |
DOI | https://doi.org/10.1051/0004-6361/202347983 | |
Published online | 14 June 2024 |
What excites the optical emission in X-ray-selected galaxies?⋆
1
Max-Planck-Institute for Astronomy, Königstuhl 17, 69117 Heidelberg, Germany
e-mail: pulatova@mpia.de
2
Main Astronomical Observatory of the National Academy of Sciences of Ukraine, Akademika Zabolotnoho str. 27, Kyiv 03143, Ukraine
3
Department of physics, Taras Shevchenko Kyiv National University, Glushkova 2 ave., building 1, Kyiv 03680, Ukraine
4
Niels Bohr Institute, Experimental Particle Physics, Blegdamsvej 17, 2100 København Copenhagen, Denmark
5
Jagiellonian University Faculty of Physics, Astronomy and Applied Computer Science, ul. prof. Stanislawa Lojasiewicza 11, 30-348 Krakow, Poland
Received:
15
September
2023
Accepted:
22
March
2024
We present a study of 1347 galaxies at z < 0.35 with detected nuclear X-ray emission and optical emission line diagnostics in the Baldwin-Phillips-Terlevich (BPT) diagram. This sample was obtained by cross-matching the XMM-Newton DR10 catalogue with Sloan Digital Sky Survey (SDSS) DR17 galaxies with well-measured line ratios. The distribution of these sources in the BPT diagram covers all three excitation regimes: Ionized Hydrogen (HII) regions (23%), ‘composites’ (30%), and Seyfert galaxies with the low ionization nuclear emission line regions (47%). In contrast, the fraction of objects classified as active galactic nuclei (AGN) in the SDSS subsample selected for cross-match with XMM-Newton is only 13%. This fact illustrates that X-ray emission from galaxies commonly points towards the presence of AGN. Our data show, for the first time, a clear dependence of the BPT position on the ratio of the X-ray to Hα fluxes. Sources dominated by X-ray emission lie in the Seyfert and LINER regimes of the BPT diagram. Most sources with a low X-ray-to-Hα-luminosity ratio, log10(LX/LHα) < 1.0, lie in the HII regime. In our sample, there are even 45 galaxies that have LXRStar/LXrayTotal > 0.5. In contrast, the positions of the sample members in the BPT diagram exhibit no dependence on the X-ray hardness ratio. Our finding suggests that the X-ray-to-Hα ratio can help us to differentiate galaxies whose X-ray flux is dominated by an AGN from galaxies with central X-ray binaries and other stellar X-ray sources.
Key words: quasars: emission lines / galaxies: Seyfert / galaxies: star formation / X-rays: galaxies
The catalogue of X-ray galaxies is available at the CDS via anonymous ftp to cdsarc.cds.unistra.fr (130.79.128.5) or via https://cdsarc.cds.unistra.fr/viz-bin/cat/J/A+A/686/A223
© The Authors 2024
Open Access article, published by EDP Sciences, under the terms of the Creative Commons Attribution License (https://creativecommons.org/licenses/by/4.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
This article is published in open access under the Subscribe to Open model.
Open access funding provided by Max Planck Society.
Current usage metrics show cumulative count of Article Views (full-text article views including HTML views, PDF and ePub downloads, according to the available data) and Abstracts Views on Vision4Press platform.
Data correspond to usage on the plateform after 2015. The current usage metrics is available 48-96 hours after online publication and is updated daily on week days.
Initial download of the metrics may take a while.