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

2024/11/21 by Pierluigi Rinaldi, Rinaldi, P., Nina Bonaventura +65 · 11 citations
Chemistry · #Astrophysics of Galaxies (astro-ph.GA) #Cosmology and Nongalactic Astrophysics (astro-ph.CO) #FOS: Physical sciences #Polydiacetylene-based materials and applications

paper · pdf · doi:10.48550/arxiv.2411.14383

openalex publication_date 2024/11/21 · openalex created_date 2025/10/10 · openalex updated_date 2026/07/30

Abstract

We analyze 99 photometrically selected Little Red Dots (LRDs) at z ≈ 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 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_\odot) = 9.07_-0.08^+0.11 for pure stellar models with A_V ≈ 1.16^+0.11-0.21 mag, and log10(M_⋆/M_\odot) = 9.67^+0.17-0.27 for models including AGNs with AV ≈ 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 is detected in 40% (FWHM = 1200-2900 km/s), 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.

Cited by

• (Re)solving the complex multi-scale morphology and V-shaped SED of a newly discovered strongly-lensed Little Red Dot in Abell 383
• Discovery of two little red dots transitioning into quasars
• The Deepest GLIMPSE of a Dense Gas Cocoon Enshrouding a Little Red Dot
• Little Red Dots as Globular Clusters in Formation
• A census of quiescent galaxies across 0.5 < z < 8 with JWST/MIRI: Mass-dependent number density evolution of quiescent galaxies in the early Universe
• A z≃0.4 Little Red Dot analog: An Extended Starburst with an Overmassive Black hole
• Limitations on Morphological Fitting for JWST "Little Red Dots"
• Spectral Uniformity of Little Red Dots: A Natural Outcome of Coevolving Seed Black Holes and Nascent Starbursts
• Beyond the Dot: an LRD-like nucleus at the Heart of an IR-Bright Galaxy and its implications for high-redshift LRDs
• Supermassive Stars Match the Spectral Signatures of JWST's Little Red Dots
• The Balmer Break and Optical Continuum of Little Red Dots from Super-Eddington Accretion

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