J/A+A/706/A136 Rest-frame NIR substructures detections (Mercier+, 2026)
Clumpiness of galaxies revealed in the near-infrared with COSMOS-Web.
Mercier W., Kalita B.S., Shuntov M., Arango-Toro R.C., Ilbert O., Tresse L.,
Dubois Y., Laigle C., Hatamnia H., McMahon N., Faisst A.L., Cox I.G.,
Trebitsch M., Michel-Dansac L., Yu S.-Y, Hirschmann M., Huertas-Company M.,
Long A.S., Koekemoer A.M., Aufort G., Lewis J.S.W., Gozaliasl G., Rich R.M.,
Rhodes J., McCracken H.J., Casey C.M., Kartaltepe J.S., Robertson B.E.,
Franco M., Liu D., Akins H.B., Allen N., Toft S.
<Astron. Astrophys. 706, A136 (2026)>
=2026A&A...706A.136M 2026A&A...706A.136M (SIMBAD/NED BibCode)
ADC_Keywords: Galaxy catalogs ; Morphology ; Infrared
Keywords: galaxies: evolution - galaxies: fundamental parameters -
galaxies: general - galaxies: statistics - galaxies: stellar content -
galaxies: structure
Abstract:
Clumps in the rest-frame UV emission of galaxies at z<3 have been
observed for decades. Since the launch of the James Webb Space
Telescope (JWST), a large population is detected in the rest-frame
near-infrared (NIR), raising questions about their formation
mechanism.
We investigate the presence and properties of NIR overdensities
(hereafter substructures, including clumps) in star-forming and
quiescent galaxies at 1<z<4 to understand their link to the
evolution of their host galaxy. Methods: We identify substructures in
JWST/NIRCam F277W and F444W residual images at a rest-frame wavelength
of 1um.
The fraction of galaxies with substructures with M*>109M☉ has
steadily decreased with cosmic time from 40% at z=4 to 10% at z=1.
NIR clumps, the most common type of small substructures, are much
fainter (2% of the total galaxy flux) than similar UV clumps in the
literature. Nearly all galaxies at the high-mass end of the main
sequence (MS), starburst, and green valley regions have substructures.
However, we do not find substructures in low-mass galaxies in the
green valley and red sequence. Although massive galaxies on the MS and
in the green valley have a 40% probability of hosting multiple clumps,
the majority of clumpy galaxies host only a single clump. Conclusions:
The fraction of clumpy galaxies in the rest-frame NIR is determined by
the stellar mass and SFR of the host galaxies. Its evolution with
redshift is due to galaxies moving toward lower SFRs at z<2 and the
build-up of low-mass galaxies in the green valley and red sequence.
Based on their spatial distribution in edge-on galaxies, we infer that
most of substructures are produced in-situ via disk fragmentation.
Galaxy mergers may still play a role at high stellar masses,
especially at low SFR.
Description:
Substructures are detected in residual images in the JWST/NIRCam F277W
bands for galaxies at 1<z<2 and F444W for those at 2<z<4.
The algorithm used for the detection of substructures can be found at:
https://github.com/WilfriedMercier/clump_finder/tree/main
The segmentation maps identifying the substructures can be found at:
https://github.com/WilfriedMercier/clump_finder/tree/main/segmaps_from_paper
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
sample.dat 516 48486 *Catalogue containing the selected sample of
galaxies with M*>109M☉ at 1<z<4
detec.dat 135 102781 Catalogue containing the substructure detections
and their properties
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Note on sample.dat: This catalogue also contains the probabilities that each
galaxy hosts exactly one, one or more, and two or more substructures
(including sub-categories such as clumps).
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See also:
J/A+A/704/A339 : COSMOS2025 (Shuntov+, 2025)
Byte-by-byte Description of file: sample.dat
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Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 6 I6 --- IDSE++ Unique identifier used to match
the galaxies to the COSMOS2025 catalogue of
Shuntov et al. (2025A&A...704A.339S 2025A&A...704A.339S,
Cat. J/A+A/704/A339, arXiv:2506.03243)
8- 31 E24.16 --- pSint=1 Probability that galaxies host exactly one
substructure of any size detected with the
intrinsic approach
33- 56 E24.16 --- pCint=1 Probability that galaxies host exactly one
clump detected with the intrinsic approach
58- 78 F21.19 --- pMint=1 Probability that galaxies host exactly one
moderately large substructure detected with
the intrinsic approach
80- 99 F20.18 --- pLint=1 Probability that galaxies host exactly one
extended substructure detected with the
intrinsic approach
101-124 E24.16 --- pSopt=1 Probability that galaxies host exactly one
substructure of any size detected with the
optimal approach
126-149 E24.16 --- pCopt=1 Probability that galaxies host exactly one
clump detected with the optimal approach
151-173 E23.15 --- pMopt=1 Probability that galaxies host exactly one
moderately large substructure detected with
the optimal approach
175-194 F20.18 --- pLopt=1 Probability that galaxies host exactly one
extended substructure detected with the
optimal approach
196-214 F19.17 --- pSint≥1 Probability that galaxies host one or more
substructures of any size detected with the
intrinsic approach
216-234 F19.17 --- pCint≥1 Probability that galaxies host one or more
clumps detected with the intrinsic approach
236-254 F19.17 --- pMint≥1 Probability that galaxies host one or more
moderately large substructures detected with
the intrinsic approach
256-274 F19.17 --- pLint≥1 Probability that galaxies host one or more
extended substructures detected with the
intrinsic approach
276-294 F19.17 --- pSopt≥1 Probability that galaxies host one or more
substructures of any size detected with the
optimal approach
296-314 F19.17 --- pCopt≥1 Probability that galaxies host one or more
clumps detected with the optimal approach
316-334 F19.17 --- pMopt≥1 Probability that galaxies host one or more
moderately large substructures detected with
the optimal approach
336-354 F19.17 --- pLopt≥1 Probability that galaxies host one or more
extended substructures detected with the
optimal approach
356-374 F19.17 --- pSint≥2 Probability that galaxies host two or more
substructures of any size detected with the
intrinsic approach
376-394 F19.17 --- pCint≥2 Probability that galaxies host two or more
clumps detected with the intrinsic approach
396-414 F19.17 --- pMint≥2 Probability that galaxies host two or more
moderately large substructures detected with
the intrinsic approach
416-434 F19.17 --- pLint≥2 Probability that galaxies host two or more
extended substructures detected with the
intrinsic approach
436-455 F20.18 --- pSopt≥2 Probability that galaxies host two or more
substructures of any size detected with the
optimal approach
457-475 F19.17 --- pCopt≥2 Probability that galaxies host two or more
clumps detected with the optimal approach
477-496 F20.18 --- pMopt≥2 Probability that galaxies host two or more
moderately large substructures detected with
the optimal approach
498-516 F19.17 --- pLopt≥2 Probability that galaxies host two or more
extended substructures detected with the
optimal approach
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Byte-by-byte Description of file: detec.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 6 I6 --- IDSE++ Unique identifier used to match the
galaxies to the COSMOS2025 catalogue of
Shuntov et al. (2025A&A...704A.339S 2025A&A...704A.339S,
Cat. J/A+A/704/A339, arXiv:2506.03243)
8- 9 I2 --- IDsub [1/38] Unique identifier for each detected
substructure (1)
11 I1 --- intrinsicsub [0/1] Whether the substructure is detected
with the intrinsic or optimal approaches
13- 30 F18.14 deg RAdeg Right ascension (J2000) of the pixel with
the highest flux associated to the
substructure
32- 49 F18.16 deg DEdeg Declination (J2000) of the pixel with the
highest flux associated to the
substructure
51- 72 F22.17 MJy/sr Flux Integrated flux of the substructure
74- 94 F21.18 arcsec2 Area Total solid angle area of the substructure
96-114 F19.17 --- Prob Probability that the given substructure
belongs to its host galaxy
116-135 F20.16 kpc2 Areakpc2 Total physical area of the substructure
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Note (1): This corresponds to the value in the segmentation map that identifies
the given substructure.
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Acknowledgements:
Wilfreid Mercier, wilfried.mercier(at)lam.fr
(End) Patricia Vannier [CDS] 25-Nov-2025