Little Red Dots and their Progenitors from Direct Collapse Black Holes

Junehyoung Jeon, Boyuan Liu, Volker Bromm, Seiji Fujimoto, Anthony J. Taylor, Vasily Kokorev, Rebecca L. Larson, John Chisholm, Steven L. Finkelstein, Dale D. Kocevski

First listed 2025-08-19 | Last updated 2026-01-10

Abstract

The James Webb Space Telescope (JWST) has discovered a new population of objects, the Little Red Dots (LRDs), characterized by V-shaped spectra indicative of strong breaks around the Balmer limit and compact morphology that gave them their name. A popular explanation is that they are a sub-population of active galactic nuclei/supermassive black holes (AGN/SMBHs) predominantly found in the high-redshift Universe ($z\gtrsim3$). Similarly, direct collapse black holes (DCBHs), theorized to form from collapsing massive, extremely metal-poor gas clouds, have been invoked to explain high-redshift quasars, the most massive AGN sub-population. Here, we employ the semi-analytical code A-SLOTH to produce a population of DCBHs and compare them against observed LRD demographics and properties. Specifically, we compare the DCBH-seeded SMBH population against the standard stellar-remnant seeds and find that DCBH models agree better with observed LRD population statistics and host halo properties. Furthermore, for the most extreme and earliest LRD detections, interpreted to be systems with an AGN but little stellar component, DCBHs are able to reproduce the observed spectral shape and properties under multiple scenarios - high dust attenuation or AGN surrounded by dense gas - that have been proposed to explain the unique shape of LRD spectra. Even when super-Eddington accretion, invoked previously to explain the nature of LRDs, is enforced on stellar remnant seeds, the spectral characteristics of extreme LRDs cannot be reproduced. We emphasize the importance of gas-metallicity observations as an additional dimension besides the widely used SMBH-stellar mass ratios to further constrain the progenitors of LRDs.

Short digest

Using the A-SLOTH semi-analytic framework, the authors generate a DCBH-seeded SMBH population and benchmark it against Little Red Dot (LRD) demographics and spectra. Heavy (DCBH) seeds reproduce the observed LRD BH mass functions, number densities, and host-halo trends better than stellar-remnant seeds. For the most extreme early LRDs (e.g., MoM-BH*-1), DCBH scenarios with either strong dust attenuation or dense, dust-free gas can match the distinctive V-shaped, Balmer-break–dominated SEDs, whereas even super-Eddington growth on light seeds cannot. The work points to gas metallicity as a crucial observable, beyond BH-to-stellar mass ratios, to pin down LRD progenitors.

Key figures to inspect

• Figure 1: Compare the modeled BH mass function and BH number densities with LRD/BLAGN measurements to see that heavy seeds track the observed LRD demographics while (super-)Eddington light seeds overproduce counts; also note the weak impact of a stricter LW threshold on massive DCBH numbers.
• Figure 2: Inspect the bolometric luminosity functions across two redshift bins—heavy seeds align with LRD LFs at lower z, while reaching the brightest luminosities requires forced super-Eddington phases that then overproduce the LF, suggesting only a rare subset of efficiently accreting heavy seeds.
• Figure 3: Examine host-halo total and cold gas reservoirs; despite slightly higher average gas masses for light (super-)Eddington seeds, heavy seeds appear more efficient at tapping cold gas, implying that gas distribution near the SMBH—not global supply—governs growth and the emergence of extreme LRDs.
• Figure 4: Study the joint distribution of central gas density and total gas mass and the evolutionary tracks; heavy seeds produce both very low and very high central densities (with the highest at early times), with rapid inflow/outflow phases that can yield gas-rich, low-stellar-mass systems reminiscent of MoM-BH*-1.
• Supplementary check: Use figure-to-text cross-references to track how dense, dust-free gas or high attenuation shapes the V-like SEDs of extreme LRDs and why light seeds fail even with super-Eddington growth.