Little Red Dots as Direct-collapse Black Hole Nurseries

TL;DR

This paper investigates whether direct-collapse black holes (DCBHs) formed in early Universe simulations could be the origin of observed Little Red Dots, a class of compact, high-redshift active galactic nuclei candidates.

Contribution

The study introduces a detailed DCBH formation model into cosmological simulations and compares the resulting DCBH population with observed properties of LRDs.

Findings

DCBH formation peaks at z>6, declining at z<6, similar to LRD emergence

DCBHs are linked to gas compaction events and intense luminosity phases

Simulated DCBHs may explain LRDs' weak X-ray and hot dust emission

Abstract

The James Webb Space Telescope recently uncovered a population of massive black holes (BHs) in the first billion years after the Big Bang. Among these high-redshift BH candidates, observations have identified a class of active galactic nuclei candidates, dubbed Little Red Dots (LRDs), with extraordinarily compact gas reservoirs and peculiar spectral features. LRDs clearly emerge at redshift z<8 and their abundance declines by z<5. Recent theoretical studies have explored the link between LRDs and the formation of heavy BH seeds in the early Universe, such as direct-collapse BHs (DCBHs). Here we present results from preliminary runs for the MELIORA cosmological hydrodynamical simulations, where we implement an accurate model for DCBH formation, accounting for the Lyman-Werner radiation field and mass-inflow rates in the target host haloes. We aim to test whether or not DCBH formation could lead to systems resembling those hypothesized for LRDs. We find that the population of newly formed DCBHs in the simulations exhibits a steep decline at z<6, akin to the emergence of LRDs, primarily driven by reduced inflows. The birth of DCBHs is associated with a significant gas compaction event, followed by a phase of intense luminosity in the 200 Myr after their birth, and subsequently by the formation of the first PopIII stars in these very haloes. If these DCBHs nurseries are associated with LRDs, then it could explain their weak emission from X-rays and hot dust.