Not Just a Dot: The Complex UV Morphology and Underlying Properties of Little Red Dots

P. Rinaldi; N. Bonaventura; G. H. Rieke; S. Alberts; K. I. Caputi; W. M. Baker; S. Baum; R. Bhatawdekar; A. J. Bunker; S. Carniani; E. Curtis-Lake; F. D’Eugenio; E. Egami; Z. Ji; B. D. Johnson; K. Hainline; J. M. Helton; X. Lin; J. Lyu; Z. Ma; R. Maiolino; P. G. Pérez-González; M. Rieke; B. E. Robertson; I. Shivaei; M. Stone; Y. Sun; S. Tacchella; H. Übler; C. C. Williams; C. N. A. Willmer; C. Willott; J. Zhang; Y. Zhu

doi:10.3847/1538-4357/adfa10

Not Just a Dot: The Complex UV Morphology and Underlying Properties of Little Red Dots

P. Rinaldi, N. Bonaventura, G. H. Rieke, S. Alberts, K. I. Caputi, W. M. Baker, S. Baum, R. Bhatawdekar, A. J. Bunker, S. Carniani, E. Curtis-Lake, F. D’Eugenio, E. Egami, Z. Ji, B. D. Johnson, K. Hainline, J. M. Helton, X. Lin, J. Lyu, Z. MaR. Maiolino, P. G. Pérez-González, M. Rieke, B. E. Robertson, I. Shivaei, M. Stone, Y. Sun, S. Tacchella, H. Übler, C. C. Williams, C. N. A. Willmer, C. Willott, J. Zhang, Y. Zhu

Research output: Contribution to journal › Article › peer-review

Abstract

We analyze 99 photometrically selected Little Red Dots (LRDs) at z ≈ 4–8 in the GOODS fields, leveraging ultradeep JADES NIRCam short-wavelength (SW) data. Among the 99 selected LRDs, we examine the morphology of 30. The remaining 69 appear predominantly compact, with sizes ≲400 pc and no extended components even in stacked SW images. However, their unresolved nature may partly reflect current depth limitations, which could prevent the detection of faint diffuse components. Among the 30 morphologically analyzed LRDs, 50% show multiple associated components, while the rest exhibit highly asymmetric structures, despite appearing as single sources. This diversity in rest-frame UV morphologies may point to interactions or strong internal feedback. We find median stellar masses of log10(M⋆/M⊙)=9.07−0.08+0.11 for pure stellar models with AV≈1.16−0.21+0.11 mag, and log10(M⋆/M⊙)=9.67−0.27+0.17 for models including active galactic nuclei (AGNs) with AV≈2.74−0.71+0.55 mag, in line with recent studies suggesting higher masses and dust content for AGN-fitted LRDs. NIRSpec spectra are available for 15 sources, six of which are also in the morphological sample. Broad Hα is detected in 40% (FWHM = 1200–2900 km s−1), and one source shows broad Hβ emission. Emission line ratios indicate a composite nature, consistent with both AGN and stellar processes. Altogether, these results suggest that LRDs are a mixed population, and their rest-frame UV morphology reflects this complexity. Morphological studies of larger samples could provide a new way to understand what drives their properties and evolution.

Original language	English
Pages (from-to)	71-90
Number of pages	20
Journal	The Astrophysical Journal
Volume	992
Issue number	1
Early online date	6 Oct 2025
DOIs	https://doi.org/10.3847/1538-4357/adfa10
Publication status	Published - 10 Oct 2025

Keywords

Near infrared astronomy
Galaxy evolution
Active galactic nuclei
James Webb Space Telescope
Galaxy formation

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© 2025 The Author(s). This is an open access article distributed under the Creative Commons Attribution License, to view a copy of the license, see: https://creativecommons.org/licenses/by/4.0/
Final published version, 14.5 MBLicence: CC BY

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Rinaldi, P., Bonaventura, N., Rieke, G. H., Alberts, S., Caputi, K. I., Baker, W. M., Baum, S., Bhatawdekar, R., Bunker, A. J., Carniani, S., Curtis-Lake, E., D’Eugenio, F., Egami, E., Ji, Z., Johnson, B. D., Hainline, K., Helton, J. M., Lin, X., Lyu, J., ... Zhu, Y. (2025). Not Just a Dot: The Complex UV Morphology and Underlying Properties of Little Red Dots. The Astrophysical Journal, 992(1), 71-90. https://doi.org/10.3847/1538-4357/adfa10

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title = "Not Just a Dot: The Complex UV Morphology and Underlying Properties of Little Red Dots",

abstract = "We analyze 99 photometrically selected Little Red Dots (LRDs) at z ≈ 4–8 in the GOODS fields, leveraging ultradeep JADES NIRCam short-wavelength (SW) data. Among the 99 selected LRDs, we examine the morphology of 30. The remaining 69 appear predominantly compact, with sizes ≲400 pc and no extended components even in stacked SW images. However, their unresolved nature may partly reflect current depth limitations, which could prevent the detection of faint diffuse components. Among the 30 morphologically analyzed LRDs, 50\% show multiple associated components, while the rest exhibit highly asymmetric structures, despite appearing as single sources. This diversity in rest-frame UV morphologies may point to interactions or strong internal feedback. We find median stellar masses of log10(M⋆/M⊙)=9.07−0.08+0.11 for pure stellar models with AV≈1.16−0.21+0.11 mag, and log10(M⋆/M⊙)=9.67−0.27+0.17 for models including active galactic nuclei (AGNs) with AV≈2.74−0.71+0.55 mag, in line with recent studies suggesting higher masses and dust content for AGN-fitted LRDs. NIRSpec spectra are available for 15 sources, six of which are also in the morphological sample. Broad Hα is detected in 40\% (FWHM = 1200–2900 km s−1), and one source shows broad Hβ emission. Emission line ratios indicate a composite nature, consistent with both AGN and stellar processes. Altogether, these results suggest that LRDs are a mixed population, and their rest-frame UV morphology reflects this complexity. Morphological studies of larger samples could provide a new way to understand what drives their properties and evolution.",

keywords = "Near infrared astronomy, Galaxy evolution, Active galactic nuclei, James Webb Space Telescope, Galaxy formation",

author = "P. Rinaldi and N. Bonaventura and Rieke, \{G. H.\} and S. Alberts and Caputi, \{K. I.\} and Baker, \{W. M.\} and S. Baum and R. Bhatawdekar and Bunker, \{A. J.\} and S. Carniani and E. Curtis-Lake and F. D{\textquoteright}Eugenio and E. Egami and Z. Ji and Johnson, \{B. D.\} and K. Hainline and Helton, \{J. M.\} and X. Lin and J. Lyu and Z. Ma and R. Maiolino and P{\'e}rez-Gonz{\'a}lez, \{P. G.\} and M. Rieke and Robertson, \{B. E.\} and I. Shivaei and M. Stone and Y. Sun and S. Tacchella and H. {\"U}bler and Williams, \{C. C.\} and Willmer, \{C. N. A.\} and C. Willott and J. Zhang and Y. Zhu",

note = "{\textcopyright} 2025 The Author(s). This is an open access article distributed under the Creative Commons Attribution License, to view a copy of the license, see: https://creativecommons.org/licenses/by/4.0/",

year = "2025",

month = oct,

day = "10",

doi = "10.3847/1538-4357/adfa10",

language = "English",

volume = "992",

pages = "71--90",

journal = "The Astrophysical Journal",

issn = "0004-637X",

publisher = "American Astronomical Society",

number = "1",

}

Rinaldi, P, Bonaventura, N, Rieke, GH, Alberts, S, Caputi, KI, Baker, WM, Baum, S, Bhatawdekar, R, Bunker, AJ, Carniani, S, Curtis-Lake, E, D’Eugenio, F, Egami, E, Ji, Z, Johnson, BD, Hainline, K, Helton, JM, Lin, X, Lyu, J, Ma, Z, Maiolino, R, Pérez-González, PG, Rieke, M, Robertson, BE, Shivaei, I, Stone, M, Sun, Y, Tacchella, S, Übler, H, Williams, CC, Willmer, CNA, Willott, C, Zhang, J & Zhu, Y 2025, 'Not Just a Dot: The Complex UV Morphology and Underlying Properties of Little Red Dots', The Astrophysical Journal, vol. 992, no. 1, pp. 71-90. https://doi.org/10.3847/1538-4357/adfa10

TY - JOUR

T1 - Not Just a Dot: The Complex UV Morphology and Underlying Properties of Little Red Dots

AU - Rinaldi, P.

AU - Bonaventura, N.

AU - Rieke, G. H.

AU - Alberts, S.

AU - Caputi, K. I.

AU - Baker, W. M.

AU - Baum, S.

AU - Bhatawdekar, R.

AU - Bunker, A. J.

AU - Carniani, S.

AU - Curtis-Lake, E.

AU - D’Eugenio, F.

AU - Egami, E.

AU - Ji, Z.

AU - Johnson, B. D.

AU - Hainline, K.

AU - Helton, J. M.

AU - Lin, X.

AU - Lyu, J.

AU - Ma, Z.

AU - Maiolino, R.

AU - Pérez-González, P. G.

AU - Rieke, M.

AU - Robertson, B. E.

AU - Shivaei, I.

AU - Stone, M.

AU - Sun, Y.

AU - Tacchella, S.

AU - Übler, H.

AU - Williams, C. C.

AU - Willmer, C. N. A.

AU - Willott, C.

AU - Zhang, J.

AU - Zhu, Y.

PY - 2025/10/10

Y1 - 2025/10/10

N2 - We analyze 99 photometrically selected Little Red Dots (LRDs) at z ≈ 4–8 in the GOODS fields, leveraging ultradeep JADES NIRCam short-wavelength (SW) data. Among the 99 selected LRDs, we examine the morphology of 30. The remaining 69 appear predominantly compact, with sizes ≲400 pc and no extended components even in stacked SW images. However, their unresolved nature may partly reflect current depth limitations, which could prevent the detection of faint diffuse components. Among the 30 morphologically analyzed LRDs, 50% show multiple associated components, while the rest exhibit highly asymmetric structures, despite appearing as single sources. This diversity in rest-frame UV morphologies may point to interactions or strong internal feedback. We find median stellar masses of log10(M⋆/M⊙)=9.07−0.08+0.11 for pure stellar models with AV≈1.16−0.21+0.11 mag, and log10(M⋆/M⊙)=9.67−0.27+0.17 for models including active galactic nuclei (AGNs) with AV≈2.74−0.71+0.55 mag, in line with recent studies suggesting higher masses and dust content for AGN-fitted LRDs. NIRSpec spectra are available for 15 sources, six of which are also in the morphological sample. Broad Hα is detected in 40% (FWHM = 1200–2900 km s−1), and one source shows broad Hβ emission. Emission line ratios indicate a composite nature, consistent with both AGN and stellar processes. Altogether, these results suggest that LRDs are a mixed population, and their rest-frame UV morphology reflects this complexity. Morphological studies of larger samples could provide a new way to understand what drives their properties and evolution.

AB - We analyze 99 photometrically selected Little Red Dots (LRDs) at z ≈ 4–8 in the GOODS fields, leveraging ultradeep JADES NIRCam short-wavelength (SW) data. Among the 99 selected LRDs, we examine the morphology of 30. The remaining 69 appear predominantly compact, with sizes ≲400 pc and no extended components even in stacked SW images. However, their unresolved nature may partly reflect current depth limitations, which could prevent the detection of faint diffuse components. Among the 30 morphologically analyzed LRDs, 50% show multiple associated components, while the rest exhibit highly asymmetric structures, despite appearing as single sources. This diversity in rest-frame UV morphologies may point to interactions or strong internal feedback. We find median stellar masses of log10(M⋆/M⊙)=9.07−0.08+0.11 for pure stellar models with AV≈1.16−0.21+0.11 mag, and log10(M⋆/M⊙)=9.67−0.27+0.17 for models including active galactic nuclei (AGNs) with AV≈2.74−0.71+0.55 mag, in line with recent studies suggesting higher masses and dust content for AGN-fitted LRDs. NIRSpec spectra are available for 15 sources, six of which are also in the morphological sample. Broad Hα is detected in 40% (FWHM = 1200–2900 km s−1), and one source shows broad Hβ emission. Emission line ratios indicate a composite nature, consistent with both AGN and stellar processes. Altogether, these results suggest that LRDs are a mixed population, and their rest-frame UV morphology reflects this complexity. Morphological studies of larger samples could provide a new way to understand what drives their properties and evolution.

KW - Near infrared astronomy

KW - Galaxy evolution

KW - Active galactic nuclei

KW - James Webb Space Telescope

KW - Galaxy formation

U2 - 10.3847/1538-4357/adfa10

DO - 10.3847/1538-4357/adfa10

M3 - Article

SN - 0004-637X

VL - 992

SP - 71

EP - 90

JO - The Astrophysical Journal

JF - The Astrophysical Journal

IS - 1

ER -

Not Just a Dot: The Complex UV Morphology and Underlying Properties of Little Red Dots

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