J/A+A/708/A373 Major merger classification in COSMOS-Web (La Marca+, 2026)
The major merger-active galactic nucleus connection up to the cosmic noon.
La Marca A., Margalef-Bentabol B., Wang L., Trager S.C.,
Rodriguez-Gomez V., Martin G.
<Astron. Astrophys. 708, A373 (2026)>
=2026A&A...708A.373L 2026A&A...708A.373L (SIMBAD/NED BibCode)
ADC_Keywords: Galaxy catalogs ; Redshifts ; ; Stars, masses ; Optical ; Infrared
Keywords: techniques: image processing - galaxies: active -
galaxies: evolution - galaxies: interactions
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 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 ∼2.5 (X-ray AGN) to ∼1.3
(MIR) and ∼1.1-1.2 (SED AGN). Similarly, AGN galaxies show a higher
merger fraction (fmerg) than non-AGN controls. We then study fmerg
as a function of relative and absolute AGN power, utilising the AGN
fraction (fAGN) and accretion disc luminosity (Ldisc) parameters.
We uncover a fmerg-fAGN relation with two regimes: fmerg stays
roughly flat for less-dominant AGN (fAGN<0.8) but increases at
fAGN>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, fmerg increases monotonically as a function of
Ldisc, for all AGN types, reaching fmerg>50% for the most luminous
AGN (Ldisc≳1046erg/s). Overall, our results suggest that major
mergers can trigger AGN out to the cosmic noon at z∼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.
Description:
Galaxy major merger classification for a stellar mass complete sample
of galaxies in COSMOS-Web, up to z=2. The catalogue includes
morphological classification and physical properties, derived through
SED fitting with the software CIGALE, for 13 789 galaxies. The parent
catalogue, COSMOS2020, is presented in Weaver et al.
(2022ApJS..258...11W 2022ApJS..258...11W, Cat. J/ApJS/258/11). The SED fitting exploited
rich multi wavelength datasets, from X-ray to far-infrared and
sub-millimetre (Wang et al., 2024A&A...688A..20W 2024A&A...688A..20W, Cat. J/A+A/688/A20).
The merger classification is performed combining two convolutional
neural networks (CNNs) trained on two different datasets: one taken
from the Illustris-TNG simulation, and one from the Horizon-AGN
simulation. Different combination of model's predictions will affect
the final classification. We refer the user to the associated
publication for full details on both the SED fitting set-up and the
morphological classification.
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
catalog.dat 327 13789 COSMOS Web Master Catalogue z=0.5-2
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See also:
J/ApJS/258/11 : The COSMOS2020 catalog (Weaver+, 2022)
J/A+A/688/A20 : COSMOS2020-MIPS-PACS-SPIRE-SCUBA catalog (Wang+, 2024)
Byte-by-byte Description of file: catalog.dat
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Bytes Format Units Label Explanations
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1- 6 I6 --- Id Farmer id from COSMOS2020 catalog (id)
8- 25 F18.14 deg RAdeg Right ascension (J2000) (RA)
27- 44 F18.16 deg DEdeg Declination (J2000) (DEC)
46- 62 F17.15 --- z Redshift (z_summary)
64 I1 --- f_z [1/3] Redshfit source (z_source) (1)
66- 77 E12.7 Msun Mstar CIGALE stellar mass (bayes.stellar.m_star)
79- 90 E12.7 Msun e_Mstar CIGALE stellar mass uncertainty
(bayes.stellar.mstarerr)
92-103 E12.7 Msun/yr SFR CIGALE star-formation rate (bayes.sfh.sfr)
105-116 E12.7 Msun/yr e_SFR CIGALE star-formation rate uncertainty
(bayes.sfh.sfr_err)
118-129 E12.7 --- fracAGN AGN fraction 3-30 micron
(bayes.agn.fracAGN)
131-142 E12.7 --- e_fracAGN AGN fraction uncertainty 3-30 micron
(bayes.agn.fracAGN_err)
144-155 E12.7 W AccPower AGN accretion power
(bayes.agn.accretion_power)
157-168 E12.7 W e_AccPower AGN accretion power uncertainty
(bayes.agn.accretionpowererr)
170-181 E12.7 W DiskLum AGN disk luminosity
(bayes.agn.disk_luminosity)
183-194 E12.7 W e_DiskLum AGN disk luminosity uncertainty
(bayes.agn.diskluminosityerr)
196-207 E12.7 W AGNLum AGN luminosity (bayes.agn.luminosity)
209-220 E12.7 W e_AGNLum AGN luminosity uncertainty
(bayes.agn.luminosity_err)
222-241 F20.16 --- chi2 chi square of best CIGALE fit
(best.chi_square)
243-261 F19.17 --- rchi2 Reduced chi square of best CIGALE fit
(best.reducedchisquare)
263-280 F18.15 --- deltarchi2 ?=- Difference on reduced chi square with
and without AGN (deltareducedchi2)
282-299 F18.15 --- relrchi2 ?=- Relative difference on reduced chi
square with and without AGN
(relativereducedchi2_change)
301-311 F11.9 --- HAModel Horizon-AGN Model predicted score
(HA Model)
313-323 F11.9 --- TNGModel Illustris-TNG Model predicted score
(TNG Model)
325-327 I3 --- MergerClass [0/1]?=-99 Merger Classification adopted
in the work (Merger Classification)
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Note (1): Redshfit source as follows:
1 = Spec-z
2 = Photo-z obtained with LePhare (COSMOS2020)
3 = Photo-z obtained with Eazy (COSMOS2020)
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Acknowledgements:
From Antonio La Marca, antonio.la.marca.astro(at)gmail.com
This research is part of the project 'Clash of the titans: deciphering
the enigmatic role of cosmic collisions' (with project number
VI.Vidi.193.113) of the research programme Vidi which is (partly)
financed by the Dutch Research Council (NWO). We would like to thank
the COSMOS-Web team for designing this project and making it possible
to have this rich, public multiwavelength data set that enables a
broad range of community science. This work is based on observations
with the NASA/ESA/CSA James Webb Space Telescope obtained from the
Barbara A. Mikulski Archive at the Space Telescope Science Institute,
which is operated by the Association of Universities for Research in
Astronomy, Incorporated, under NASA contract NAS5-03127. Support for
Program Nos. JWST-GO-02057 and JWST-AR-03038 was provided through a
grant from the STScI under NASA contract NAS5-03127.
License: CC-BY-4.0 [see https://spdx.org/licenses/]
(End) Patricia Vannier [CDS] 11-Mar-2026