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Peer-reviewedCC BYPublications of the Astronomical Society of Japan

Hidden in Pixels. I. Discovery of dual “little red dots” indicates excess clustering on kilo-parsec scales

  • Takumi S. Tanaka1,2,3
  • John D. Silverman4,1,2,3
  • Kazuhiro Shimasaku2,5
  • Junya Arita2
  • Hollis B. Akins6
  • Feige Wang7
  • Kohei Inayoshi8
  • Xuheng Ding9
  • Masafusa Onoue10,8,3,11
  • Zhaoxuan Liu1,2,3
  • Caitlin M. Casey12,6,13
  • Erini Lambrides14
46 more authors
  • Vasily Kokorev6,15
  • Shuowen Jin12,16
  • Andreas L. Faisst17
  • Jianwei Lyu18
  • Jan–Torge Schindler19
  • Yunjing Wu3
  • Nicole E. Drakos20
  • Yue Guo Shen21,22
  • Junyao Li21
  • Ming-Yang Zhuang21
  • Qinyue Fei23,24
  • Kei Ito12,16
  • Wei Leong Tee18
  • Weizhe Liu18
  • Wenke Ren25,26
  • T. Kiyota27,28
  • Zijian Li29,30
  • Suin Matsui2
  • Makoto Ando31,28
  • Shun Hatano32
  • Michiko S. Fujii2
  • Jeyhan S. Kartaltepe33
  • Anton M. Koekemoer34
  • Daizhong Liu35
  • Henry Joy McCracken36
  • Jason D. Rhodes37
  • Brant E. Robertson38
  • Maximilien Franco6,39
  • Koki Kakiichi12,40
  • Jinyi Yang7
  • R. A. Meyer
  • I.T Andika
  • Aidan P. Cloonan
  • Xiaohui Fan18
  • G. Gozaliasl
  • Santosh Harish33
  • Christopher C. Hayward
  • Darshan Kakkad34
  • Tomoya Kinugawa5
  • Mingyu Li
  • Namrata Roy4
  • Marko Shuntov12,40
  • M. Talia
  • Sune Toft12,40
  • Aswin P. Vijayan12,16
  • Yiyang Zhang9
40 affiliations
  1. 1Center for Data-Driven Discovery, Kavli IPMU (WPI), UTIAS, The University of Tokyo , 5-1-5 Kashiwanoha, Kashiwa, Chiba 277-8583 ,
  2. 2Department of Astronomy, Graduate School of Science, The University of Tokyo , 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-0033 ,
  3. 3Kavli Institute for the Physics and Mathematics of the Universe (WPI), The University of Tokyo Institutes for Advanced Study, The University of Tokyo , 5-1-5 Kashiwanoha, Kashiwa, Chiba 277-8583 ,
  4. 4Center for Astrophysical Sciences, Department of Physics and Astronomy, Johns Hopkins University , 3400 N. Charles Street, Baltimore, MD 21218 ,
  5. 5Research Center for the Early Universe, Graduate School of Science, The University of Tokyo , 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-0033 ,
  6. 6Department of Astronomy, The University of Texas at Austin , 2515 Speedway Boulevard Stop C1400, Austin, TX 78712 ,
  7. 7Department of Astronomy, University of Michigan , 1085 S. University Avenue, Ann Arbor, MI 48109 ,
  8. 8Kavli Institute for Astronomy and Astrophysics, Peking University , Beijing 100871 ,
  9. 9School of Physics and Technology, Wuhan University , Wuhan 430072 ,
  10. 10Center for Data Science, Waseda University , 1-6-1 Nishi-Waseda, Shinjuku, Tokyo 169-0051 ,
  11. 11Waseda Institute for Advanced Study (WIAS), Waseda University , 1-21-1 Nishi-Waseda, Shinjuku, Tokyo 169-0051 ,
  12. 12Cosmic Dawn Center (DAWN), Niels Bohr Building , Radmandsgade 62–64, DK-2200 Copenhagen N ,
  13. 13Department of Physics, University of California, Santa Barbara , Broida Hall, Santa Barbara, CA 93109-9530 ,
  14. 14NASA-Goddard Space Flight Center , Code 662, Greenbelt, MD, 20771 ,
  15. 15Kapteyn Astronomical Institute, University of Groningen , 9700 AV Groningen ,
  16. 16DTU Space, Technical University of Denmark, Elektrovej , Building 328, 2800, Kgs. Lyngby ,
  17. 17Caltech/IPAC , 1200 E. California Blvd. Pasadena, CA 91125 ,
  18. 18Steward Observatory, University of Arizona , 933 N Cherry Avenue, Tucson, AZ 85721 ,
  19. 19Hamburger Sternwarte, University of Hamburg , Gojenbergsweg 112, D-21029 Hamburg ,
  20. 20Department of Physics and Astronomy, University of Hawaii , Hilo, 200 W Kawili St., Hilo, HI 96720 ,
  21. 21Department of Astronomy, University of Illinois at Urbana-Champaign , Urbana, IL 61801 ,
  22. 22National Center for Supercomputing Applications, University of Illinois at Urbana-Champaign , Urbana, IL 61801 ,
  23. 23David A. Dunlap Department of Astronomy and Astrophysics, University of Toronto , 50 St. George Street, Toronto, Ontario, M5S 3H4 ,
  24. 24Department of Astronomy, School of Physics, Peking University , Beijing 100871 ,
  25. 25CAS Key Laboratory for Research in Galaxies and Cosmology, Department of Astronomy, University of Science and Technology of China , Hefei, Anhui 230026 ,
  26. 26School of Astronomy and Space Science, University of Science and Technology of China , Hefei 230026 ,
  27. 27Department of Astronomical Science, The Graduate University for Advanced Studies , SOKENDAI, 2-21-1 Osawa, Mitaka, Tokyo, 181-8588 ,
  28. 28National Astronomical Observatory of Japan , 2-21-1 Osawa, Mitaka, Tokyo, 181-8588 ,
  29. 29Chinese Academy of Sciences South America Center for Astronomy (CASSACA), National Astronomical Observatories of China (NAOC) , CAS, 20A Datun Road, Beijing 100012 ,
  30. 30School of Astronomy and Space Sciences, University of Chinese Academy of Sciences , Beijing 100049 ,
  31. 31Institute for Cosmic Ray Research, The University of Tokyo , 5-1-5 Kashiwanoha, Kashiwa, Chiba 277-8582 ,
  32. 32Department of Astronomical Science, SOKENDAI (The Graduate University for Advanced Studies) , Osawa 2-21-1, Mitaka, Tokyo, 181-8588 ,
  33. 33Laboratory for Multiwavelength Astrophysics, School of Physics and Astronomy, Rochester Institute of Technology , 84 Lomb Memorial Drive, Rochester, NY 14623 ,
  34. 34Space Telescope Science Institute , 3700 San Martin Drive, Baltimore, MD 21218 ,
  35. 35Purple Mountain Observatory, Chinese Academy of Sciences , 10 Yuanhua Road, Nanjing 210023 ,
  36. 36Institut d’Astrophysique de Paris , UMR 7095, CNRS, and Sorbonne Université, 98 bis boulevard Arago, 75014 Paris ,
  37. 37Jet Propulsion Laboratory, California Institute of Technology , 4800 Oak Grove Drive, Pasadena, CA 91001 ,
  38. 38Department of Astronomy and Astrophysics, University of California, Santa Cruz , 1156 High Street, Santa Cruz, CA 95064 ,
  39. 39Université Paris-Saclay, Université Paris Cité , CEA, CNRS, AIM, 91191 Gif-sur-Yvette ,
  40. 40Niels Bohr Institute, University of Copenhagen , Jagtvej 128, DK-2200 Copenhagen N ,
Open at sourceDOICite

Abstract

‘‘Little Red Dots” (LRDs) are an abundant high-redshift population newly discovered by the James Webb Space Telescope (JWST) and considered to be an early growth phase of supermassive black holes (SMBHs). Using a method of pixel-by-pixel color selection and relaxing the compactness criteria, we identify four dual LRD candidates in the COSMOS-Web survey with projected separations of 0.′′ 2–1.′′ 2. A comparison between existing LRD samples and mock data reveals that the projected separations of these dual LRD candidates are unlikely to result from chance projections of objects at different redshifts. Furthermore, two of the four systems are covered by COSMOS-3D slitless spectroscopy, and a single-line detection at the same observed wavelength for each LRD in a pair strongly supports that they are at identical redshifts. Assuming that the detected lines are Hα based on its high equivalent width and broad profile, the spectroscopic redshifts of z=5.822 and 5.464 for the two pairs are consistent with their photometric redshifts, yielding projected separations of 1.64 and 7.36 kpc. These discoveries suggest that the angular auto-correlation function (ACF) of LRDs exhibits an excess (∼ 50 times) on sub-arcsec (kilo-parsec) separations compared to an extrapolation of a power-law ACF of LRDs measured over 10′ ′ –100′ ′ . Our sample is likely to represent precursors of mergers between LRDs, and such mergers may be one of the mechanisms that can drive the rapid growth of SMBHs in their early evolutionary stages.

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Cite

BibTeXRIS
BibTeX
@article{tanaka2026hidden,
  title = {{Hidden in Pixels. I. Discovery of dual “little red dots” indicates excess clustering on kilo-parsec scales}},
  author = {Takumi S. Tanaka and John D. Silverman and Kazuhiro Shimasaku and Junya Arita and Hollis B. Akins and Feige Wang and Kohei Inayoshi and Xuheng Ding and Masafusa Onoue and Zhaoxuan Liu and Caitlin M. Casey and Erini Lambrides and Vasily Kokorev and Shuowen Jin and Andreas L. Faisst and Jianwei Lyu and Jan–Torge Schindler and Yunjing Wu and Nicole E. Drakos and Yue Guo Shen and Junyao Li and Ming-Yang Zhuang and Qinyue Fei and Kei Ito and Wei Leong Tee and Weizhe Liu and Wenke Ren and T. Kiyota and Zijian Li and Suin Matsui and Makoto Ando and Shun Hatano and Michiko S. Fujii and Jeyhan S. Kartaltepe and Anton M. Koekemoer and Daizhong Liu and Henry Joy McCracken and Jason D. Rhodes and Brant E. Robertson and Maximilien Franco and Koki Kakiichi and Jinyi Yang and R. A. Meyer and I.T Andika and Aidan P. Cloonan and Xiaohui Fan and G. Gozaliasl and Santosh Harish and Christopher C. Hayward and Darshan Kakkad and Tomoya Kinugawa and Mingyu Li and Namrata Roy and Marko Shuntov and M. Talia and Sune Toft and Aswin P. Vijayan and Yiyang Zhang},
  journal = {Publications of the Astronomical Society of Japan},
  year = {2026},
  month = jul,
  doi = {10.1093/pasj/psag092},
  url = {https://doi.org/10.1093/pasj/psag092},
  note = {CC BY},
}
RIS
TY  - JOUR
TI  - Hidden in Pixels. I. Discovery of dual “little red dots” indicates excess clustering on kilo-parsec scales
AU  - Takumi S. Tanaka
AU  - John D. Silverman
AU  - Kazuhiro Shimasaku
AU  - Junya Arita
AU  - Hollis B. Akins
AU  - Feige Wang
AU  - Kohei Inayoshi
AU  - Xuheng Ding
AU  - Masafusa Onoue
AU  - Zhaoxuan Liu
AU  - Caitlin M. Casey
AU  - Erini Lambrides
AU  - Vasily Kokorev
AU  - Shuowen Jin
AU  - Andreas L. Faisst
AU  - Jianwei Lyu
AU  - Jan–Torge Schindler
AU  - Yunjing Wu
AU  - Nicole E. Drakos
AU  - Yue Guo Shen
AU  - Junyao Li
AU  - Ming-Yang Zhuang
AU  - Qinyue Fei
AU  - Kei Ito
AU  - Wei Leong Tee
AU  - Weizhe Liu
AU  - Wenke Ren
AU  - T. Kiyota
AU  - Zijian Li
AU  - Suin Matsui
AU  - Makoto Ando
AU  - Shun Hatano
AU  - Michiko S. Fujii
AU  - Jeyhan S. Kartaltepe
AU  - Anton M. Koekemoer
AU  - Daizhong Liu
AU  - Henry Joy McCracken
AU  - Jason D. Rhodes
AU  - Brant E. Robertson
AU  - Maximilien Franco
AU  - Koki Kakiichi
AU  - Jinyi Yang
AU  - R. A. Meyer
AU  - I.T Andika
AU  - Aidan P. Cloonan
AU  - Xiaohui Fan
AU  - G. Gozaliasl
AU  - Santosh Harish
AU  - Christopher C. Hayward
AU  - Darshan Kakkad
AU  - Tomoya Kinugawa
AU  - Mingyu Li
AU  - Namrata Roy
AU  - Marko Shuntov
AU  - M. Talia
AU  - Sune Toft
AU  - Aswin P. Vijayan
AU  - Yiyang Zhang
PY  - 2026
DA  - 2026/07/09
JO  - Publications of the Astronomical Society of Japan
DO  - 10.1093/pasj/psag092
UR  - https://doi.org/10.1093/pasj/psag092
AB  - ‘‘Little Red Dots” (LRDs) are an abundant high-redshift population newly discovered by the James Webb Space Telescope (JWST) and considered to be an early growth phase of supermassive black holes (SMBHs). Using a method of pixel-by-pixel color selection and relaxing the compactness criteria, we identify four dual LRD candidates in the COSMOS-Web survey with projected separations of 0_.^′′ 2–1_.^′′ 2. A comparison between existing LRD samples and mock data reveals that the projected separations of these dual LRD candidates are unlikely to result from chance projections of objects at different redshifts. Furthermore, two of the four systems are covered by COSMOS-3D slitless spectroscopy, and a single-line detection at the same observed wavelength for each LRD in a pair strongly supports that they are at identical redshifts. Assuming that the detected lines are Hα based on its high equivalent width and broad profile, the spectroscopic redshifts of z=5.822 and 5.464 for the two pairs are consistent with their photometric redshifts, yielding projected separations of 1.64 and 7.36 kpc. These discoveries suggest that the angular auto-correlation function (ACF) of LRDs exhibits an excess (∼ 50 times) on sub-arcsec (kilo-parsec) separations compared to an extrapolation of a power-law ACF of LRDs measured over 10^′ ′ –100^′ ′ . Our sample is likely to represent precursors of mergers between LRDs, and such mergers may be one of the mechanisms that can drive the rapid growth of SMBHs in their early evolutionary stages.
SN  - 0004-6264
SN  - 2053-051X
ER  -