The major merger-active galactic nucleus connection up to the cosmic noon

A. La Marca; B. Margalef-Bentabol; L. Wang; S. C. Trager; V. Rodriguez-Gomez; G. Martin

doi:10.1051/0004-6361/202555185

paper

The major merger-active galactic nucleus connection up to the cosmic noon

arXiv:2602.19997 · doi:10.1051/0004-6361/202555185

Abstract

Galaxy major mergers are a potential mechanism for triggering active galactic nuclei (AGN) activity, but their role remains debated, particularly beyond the local Universe. We aim to shed light on the merger-AGN connection at $z = 0.5$ - $2$ , exploiting the multi-wavelength datasets and {\it James Webb Space Telescope} (JWST) observations in the COSMOS field. We construct a stellar mass-limited sample and identify AGN via mid-infrared (MIR) colours, X-ray detections, and spectral energy distribution (SED) fitting. We train convolutional neural networks to identify mergers with mock JWST observations. We create non-AGN and non-merger control samples matching the redshift, stellar mass, and star-formation rate distributions of the AGN and mergers. We find AGN to be moderately more frequent in mergers than in non-mergers, with excess ratios ranging from $\sim 2.5$ (X-ray AGN) to $\sim 1.3$ (MIR) and $\sim 1.1$ -1.2 (SED AGN). Similarly, AGN galaxies show a higher merger fraction ( $f_{m er g}$ ) than non-AGN controls. We then study $f_{m er g}$ as a function of relative and absolute AGN power, utilising the AGN fraction ( $f_{A GN}$ ) and accretion disc luminosity (L $_{d i sc}$ ) parameters. We uncover a $f_{m er g}$ - $f_{A GN}$ relation with two regimes: $f_{m er g}$ stays roughly flat for less-dominant AGN ( $f_{A GN} < 0.8$ ) but increases at $f_{A GN} > 0.8$ for the MIR and X-ray AGN, and more gently for SED AGN, where mergers appear to be the main triggering mechanism. Additionally, $f_{m er g}$ increases monotonically as a function of L $_{d i sc}$ , for all AGN types, reaching $f_{m er g} > 50%$ for the most luminous AGN (L $_{d i sc} ≳ 1 0^{46} er g s^{- 1}$ ). Overall, our results suggest that major mergers can trigger AGN out to the cosmic noon at $z \sim 2$ . Furthermore, the role of major mergers shows a clear dependence on AGN luminosity and remains the principal mechanism for fuelling the most powerful AGN.

arXiv comment18 pages (5 pages Appendix), 22 Figures. Submitted to A&A: accepted for publication after minor revision

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