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<p>The James Webb Space Telescope has revealed a new class of high-redshift, very red, compact broad-line sources, termed ‘little red dots’ (LRDs). The physical mechanism driving these properties remains elusive. Here we construct spectral energy distributions with a spectroscopic redshift for 28 LRDs, finding that they have V-shaped SEDs with a common break frequency of <i>ν</i><sub>b</sub> ≈ 10<sup>14.96±0.06</sup> Hz. We propose that these unique SEDs can be explained well by the combination of an inner standard disk and an outer gravitationally unstable accretion disk with Toomre parameter <i>Q</i> ≈ 1. The outer disk has a temperature of ~2,000–4,000 K and mainly radiates in near-infrared-to-optical wavebands. The composite spectrum from this model naturally explains the V-shaped continuum and reproduces the intrinsically luminous infrared-to-optical emission without requiring extreme dust extinction or unusual stellar populations. Even when we considered possible dense gas around the disk to account for pronounced Balmer breaks in some LRDs, the intrinsic optical-to-ultraviolet emission is suppressed by factors of only ≲2–3, which indicates that most LRDs are sub-Eddington and intrinsically weak. These results provide new insights into early-phase black hole growth and galaxy evolution.</p>

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The composite spectrum of little red dots from a standard inner disk and an unstable outer disk

  • 期刊论文

  • 发表日期：

    2026年2月5日

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  • Chenxuan Zhang,
  • Qingwen Wu,
  • Xiao Fan,
  • Luis C. Ho,
  • Jiancheng Wu,
  • Huanian Zhang,
  • Bing Lyu,
  • Xinwu Cao,
  • Jianmin Wang

摘要

The James Webb Space Telescope has revealed a new class of high-redshift, very red, compact broad-line sources, termed ‘little red dots’ (LRDs). The physical mechanism driving these properties remains elusive. Here we construct spectral energy distributions with a spectroscopic redshift for 28 LRDs, finding that they have V-shaped SEDs with a common break frequency of νb ≈ 1014.96±0.06 Hz. We propose that these unique SEDs can be explained well by the combination of an inner standard disk and an outer gravitationally unstable accretion disk with Toomre parameter Q ≈ 1. The outer disk has a temperature of ~2,000–4,000 K and mainly radiates in near-infrared-to-optical wavebands. The composite spectrum from this model naturally explains the V-shaped continuum and reproduces the intrinsically luminous infrared-to-optical emission without requiring extreme dust extinction or unusual stellar populations. Even when we considered possible dense gas around the disk to account for pronounced Balmer breaks in some LRDs, the intrinsic optical-to-ultraviolet emission is suppressed by factors of only ≲2–3, which indicates that most LRDs are sub-Eddington and intrinsically weak. These results provide new insights into early-phase black hole growth and galaxy evolution.