English

Not Just a Dot: the complex UV morphology and underlying properties of Little Red Dots

Astrophysics of Galaxies 2025-10-03 v2 Cosmology and Nongalactic Astrophysics

Abstract

We analyze 99 photometrically selected Little Red Dots (LRDs) at z48z \approx 4-8 in the GOODS fields, leveraging ultra-deep JADES NIRCam short-wavelength (SW) data. We examine the morphology of 30 LRDs, while the remaining 69 appear predominantly compact, with sizes 400\leq 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)=9.070.08+0.11\log_{10}(M_{\star}/M_{\odot}) = 9.07_{-0.08}^{+0.11} for pure stellar models with AV1.16+0.110.21A_{V} \approx 1.16^{+0.11}{-0.21} mag, and log10(M/M)=9.67+0.170.27\log{10}(M_{\star}/M_{\odot}) = 9.67^{+0.17}{-0.27} for models including AGNs with AV2.740.71+0.55A{V} \approx 2.74^{+0.55}_{-0.71} 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\alpha is detected in 40% (FWHM = 1200-2900 km/s), and one source shows broad Hβ\beta 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

Cite

@article{arxiv.2411.14383,
  title  = {Not Just a Dot: the complex UV morphology and underlying properties of Little Red Dots},
  author = {P. Rinaldi and N. Bonaventura and G. H. Rieke and S. Alberts and K. I. Caputi and W. M. Baker and S. Baum and R. Bhatawdekar and A. J. Bunker and S. Carniani and E. Curtis-Lake and F. D'Eugenio and E. Egami and Z. Ji and K. Hainline and J. M. Helton and X. Lin and J. Lyu and B. D. Johnson and Z. Ma and R. Maiolino and P. G. Pérez-González and M. Rieke and B. E. Robertson and I. Shivaei and M. Stone and Y. Sun and S. Tacchella and H. Übler and C. C. Williams and C. N. A. Willmer and C. Willott and J. Zhang and Y. Zhu},
  journal= {arXiv preprint arXiv:2411.14383},
  year   = {2025}
}

Comments

28 pages, 10 figures, 3 tables. Accepted for publication in ApJ