Dust and Power: Unravelling the merger - active galactic nucleus connection in the second half of cosmic history

A. La Marca; B. Margalef-Bentabol; L. Wang; F. Gao; A. D. Goulding; G. Martin; V. Rodriguez-Gomez; S. C. Trager; G. Yang; R. Davé; Y. Dubois

doi:10.1051/0004-6361/202348188

paper

Dust and Power: Unravelling the merger - active galactic nucleus connection in the second half of cosmic history

arXiv:2407.18238 · doi:10.1051/0004-6361/202348188

Abstract

Galaxy mergers represent a fundamental physical process under hierarchical structure formation, but their role in triggering AGNs is still unclear. We aim to investigate the merger-AGN connection using state-of-the-art observations and novel methods in detecting mergers and AGNs. We selected stellar mass-limited samples at redshift z<1 from KiDS, focusing on the KiDS-N-W2 field with a wide range of multi-wavelength data. Three AGN types, selected in the MIR, X-ray, and via SED modelling, were analysed. To identify mergers, we used convolutional neural networks trained on two cosmological simulations. We created mass and redshift-matched control samples of non-mergers and non-AGNs. We observe a clear AGN excess (a factor of 2-3) in mergers with respect to non-mergers for the MIR AGNs, and a mild excess for the X-ray and SED AGNs, indicating that mergers could trigger all 3 types but are more connected with the MIR AGNs. About half of the MIR AGNs are in mergers but it is unclear whether mergers are the main trigger. For the X-ray and SED AGNs, mergers are unlikely to be the dominant trigger. We also explore the relation using the continuous AGN fraction $f_{A GN}$ parameter. Mergers exhibit a clear excess of high $f_{A GN}$ values relative to non-mergers, for all AGNs. We unveil the first merger fraction $f_{m er g} - f_{A GN}$ relation with two distinct regimes. When the AGN is not dominant, the relation is only mildly increasing or even flat, with the MIR AGNs showing the highest $f_{m er g}$ . In the regime of very dominant AGNs ( $f_{A GN} \geq 0.8$ ), $f_{m er g}$ shows a steeply rising trend with increasing $f_{A GN}$ for all AGN types. These trends are also seen when plotted against AGN bolometric luminosity. We conclude that mergers are most connected with dust-obscured AGNs (linked to a fast-growing phase of the SMBH) and are the main or even the sole fuelling mechanism of the most powerful AGNs.

arXiv comment24 pages, 17 figures, 6 Appendix pages. Public available multi-wavelength catalogue of galaxies. Accepted for publication in A&A

Dust and Power: Unravelling the merger - active galactic nucleus connection in the second half of cosmic history

Abstract

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