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Little Red Dots as the Very First Activity of Black Hole Growth

Kohei Inayoshi

TL;DR

This paper identifies Little Red Dots (LRDs) as a high-redshift, early-phase AGN population detected by JWST that emerges around $z\sim6$–8 and declines by $z<4$. By assembling 341 LRDs across $z\sim2$–11, the authors demonstrate that a log-normal distribution best describes the occurrence times of LRD activity and derive an analytic redshift-evolution form for their abundance, enabling direct comparison with future observations. The authors argue that LRDs represent the first accretion episodes of newly formed seed black holes in dense environments, potentially with super-Eddington bursts, and that their features fade as black holes grow, explaining their overmassive nature and transition to normal AGN activity. They provide an analytic framework linking early LRD activity to the broader AGN population, including the emergence of X-ray detected AGNs at $4<z<6$, and discuss the role of mergers and environmental factors in shaping the observed evolution.

Abstract

The James Webb Space Telescope has detected massive black holes (BHs) with masses of $\sim 10^{6-8}~M_\odot$ within the first billion years of the universe. One of the remarkable findings is the identification of "Little Red Dots" (LRDs), a unique class of active galactic nuclei (AGNs) with distinct characteristics representing a key phase in the formation and growth of early BHs. Here, we analyze the occurrence rate of LRDs, which emerge around redshifts $z \sim 6-8$ and sharply decline at $z < 4$. We find that this trend follows a log-normal distribution, commonly observed in phenomena driven by stochastic and random factors. We propose a hypothesis that the first one or two AGN events associated with newly-formed seed BHs are observed as LRDs and their unique features fade in the subsequent episodes. This naturally explains the cosmic evolution of AGN abundance over $0 < z < 5$, which follows $\propto (1+z)^{-5/2}$ due to the cumulative effect of recurring AGN activity. The unique characteristics of LRDs are likely linked to the dense gas environments around the seed BHs, which create strong absorption features in the broad-line emission and enable super-Eddington accretion bursts, ultimately yielding the observed overmassive nature of BHs compared to the local relationship. An analytical expression for the redshift evolution of LRD abundance is provided for direct comparison with future observational constraints.

Little Red Dots as the Very First Activity of Black Hole Growth

TL;DR

This paper identifies Little Red Dots (LRDs) as a high-redshift, early-phase AGN population detected by JWST that emerges around –8 and declines by . By assembling 341 LRDs across –11, the authors demonstrate that a log-normal distribution best describes the occurrence times of LRD activity and derive an analytic redshift-evolution form for their abundance, enabling direct comparison with future observations. The authors argue that LRDs represent the first accretion episodes of newly formed seed black holes in dense environments, potentially with super-Eddington bursts, and that their features fade as black holes grow, explaining their overmassive nature and transition to normal AGN activity. They provide an analytic framework linking early LRD activity to the broader AGN population, including the emergence of X-ray detected AGNs at , and discuss the role of mergers and environmental factors in shaping the observed evolution.

Abstract

The James Webb Space Telescope has detected massive black holes (BHs) with masses of within the first billion years of the universe. One of the remarkable findings is the identification of "Little Red Dots" (LRDs), a unique class of active galactic nuclei (AGNs) with distinct characteristics representing a key phase in the formation and growth of early BHs. Here, we analyze the occurrence rate of LRDs, which emerge around redshifts and sharply decline at . We find that this trend follows a log-normal distribution, commonly observed in phenomena driven by stochastic and random factors. We propose a hypothesis that the first one or two AGN events associated with newly-formed seed BHs are observed as LRDs and their unique features fade in the subsequent episodes. This naturally explains the cosmic evolution of AGN abundance over , which follows due to the cumulative effect of recurring AGN activity. The unique characteristics of LRDs are likely linked to the dense gas environments around the seed BHs, which create strong absorption features in the broad-line emission and enable super-Eddington accretion bursts, ultimately yielding the observed overmassive nature of BHs compared to the local relationship. An analytical expression for the redshift evolution of LRD abundance is provided for direct comparison with future observational constraints.

Paper Structure

This paper contains 6 sections, 7 equations, 4 figures, 1 table.

Table of Contents

  1. Introduction
  2. Cosmic Evolution of LRD Numbers
  3. Discussion
  4. Selection
  5. Diminishing LRD features due to mergers with other galaxies
  6. Analytic formula

Figures (4)

  • Figure 1: Left: The occurrence rate of LRDs as a function of cosmic time (bottom $x$-axis) and redshift (top $x$-axis). The histogram, based on the data from Kocevski_2025, shows 341 photometrically-selected LRDs (blue), including 39 with spectroscopically-confirmed redshifts (green). The colored bars indicate the redshift range where the $4000~{\rm \AA}$ break falls within the bandpass of each wide-band filter. The photometric selection of $z>9$ LRDs becomes incomplete (gray shaded region). The magenta curve represents the best-fit function with a log-normal distribution, while the gray curve shows the case with constant abundance in unit comoving volume for reference. Right: The cumulative number distribution of the observed LRD number (blue) with error bars computed via binomial statistics. The best-fit result obtained using a log-normal distribution is shown ($p=0.873$), along with a Gaussian distribution yielding a worse fit ($p=1.17\times 10^{-4}$).
  • Figure 2: Left: The redshift dependence of the AGN comoving number density. Each modeled curve presents the AGN population that undergo $n$-th AGN active episodes, illustrating the distribution of the total elapsed time $T_n$ ($1\leq n\leq 8$): the first (magenta), second (green), third (cyan), fourth (orange) episodes, as well as the total population in this model (black). The normalization is set such that the modeled LRD abundance is consistent with the observed ones Kokorev_2024aKocevski_2025. The predicted abundance in this model agrees with those of LRD candidates at $1.7<z<3.7$ photometrically selected by wide-area ground-based telescope surveys Ma_2025, as well as with X-ray selected AGNs over $0<z<5$Ueda_2014 and $4<z<6$Pouliasis_2024. Right: The fraction of non-LRDs (black curve; model) and observational constraints on the fraction (95% confidence level) derived from a sample of 62 broad-line AGNs Taylor_2025a.
  • Figure 3: Left: The distribution of UV absolute magnitudes for LRDs with the total sample (purple) and subsets at $z\geq 6$ (green), $z\geq 7$ (blue), and $z\geq 8$ (orange). The vertical line indicates a reference threshold of $M_{\rm UV}=-18$ mag, fainter than which the observed decline in number is likely due to flux limits. Right: The LRD occurrence rate for the total sample (purple) and subsets at $M_{\rm UV}<-18$ (green) and $M_{\rm UV}<-19$ (blue) overlaid with best-fit log-normal distributions (solid curves).
  • Figure 4: The LRD occurrence-rate models: the log-normal case (magenta) and the decay cases driven by mergers: $p=0$ (gray), $p=0.2$ (cyan), and $p=0.5$ (blue).